Adding tasks to RecyclerView

Adding tasks to RecyclerView - java

I'm new to Android and have been learning about Android app development for about a month just through a book, and right now, I'm working on my own project, which is a basic app that manages user tasks and schedule. There is this one problem I am having. I am trying to add a new task to a RecyclerView list that contains the list of main tasks, but I keep getting errors. Here is what I have (I don't want to show everything because it is a project):
The RecyclerView list (main_task_window.xml):
<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout
xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
android:layout_width="match_parent"
android:layout_height="match_parent">
<android.support.v7.widget.RecyclerView
android:id="#+id/MainTaskList"
android:layout_width="match_parent"
android:layout_height="449dp"
android:layout_alignParentStart="true"
android:layout_alignParentBottom="true"
android:layout_marginStart="0dp"
android:layout_marginTop="1dp"
android:layout_marginBottom="61dp" />
<android.support.design.widget.FloatingActionButton
android:id="#+id/AddaMainTask"
android:onClick="addnewtask"
android:layout_width="54dp"
android:layout_height="51dp"
android:layout_alignParentEnd="true"
android:layout_alignParentBottom="true"
android:layout_marginEnd="13dp"
android:layout_marginBottom="10dp"
android:clickable="true"
app:srcCompat="#android:drawable/ic_input_add" />
</RelativeLayout>
The window that allows users to add new main tasks as well as additional notes (add_new_main_task_window.xml):
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout
xmlns:android="http://schemas.android.com/apk/res/android"
android:orientation="vertical"
android:layout_width="match_parent"
android:layout_height="match_parent">
<EditText
android:id="#+id/maintasks"
android:layout_width="match_parent"
android:layout_height="62dp"
android:hint="Main Task"/>
<EditText
android:id="#+id/notes"
android:layout_width="match_parent"
android:layout_height="62dp"
android:hint="Additional notes"/>
<Button
android:id="#+id/addButton"
android:onClick="sendButton"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:text="Add to main task" />
</LinearLayout>
Now here are the following Java files:
1. MainTasks.java (contains the get and set methods for the main task and additional notes)
package com.ricstudios.daymanager;
public class MainTasks
{
private String mt, an; //'mt' stands for "main tasks". 'an' stands for "additional notes"
//MainTasks class constructor
public MainTasks(String mt, String an)
{
//mt and an in the parameters is equal to the mt and an variables above
this.mt = mt;
this.an = an;
}
public String getMainTasks() //this get method obtains the main task string input)
{
return mt;
}
public void setMainTasks(String MainTasks) //this set methods stores the main task string input)
{
this.mt = MainTasks;
}
public String getAdditionalNotes() //this get method obtains the main task string input
{
return an;
}
public void setAdditionalNotes(String AddNotes) //this set method stores the main task string
{
this.an = AddNotes;
}
}
MainTaskAdapter.java (contains the adapter to render the data)
package com.ricstudios.daymanager;
import android.support.v7.widget.RecyclerView;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.EditText;
import java.util.List;
public class MainTaskAdapter extends RecyclerView.Adapter<MainTaskAdapter.ViewHolder>
{
private List<MainTasks> maintasklist; //will contain the main task and additional notes string inputs
public class ViewHolder extends RecyclerView.ViewHolder
{
public EditText maintask, addnotes;
//provides a reference to the views for each data item
public ViewHolder(View view)
{
super(view);
maintask = (EditText)view.findViewById(R.id.maintasks);
addnotes = (EditText)view.findViewById(R.id.notes);
}
}
//MainTaskAdapter class constructor
public MainTaskAdapter(List<MainTasks> maintasklist)
{
this.maintasklist = maintasklist;
}
//create new view (invoked by the layout manager)
#Override
public ViewHolder onCreateViewHolder(ViewGroup parent, int viewType)
{
View itemView = LayoutInflater.from(parent.getContext()).inflate(R.layout.add_new_main_task_window, parent, false);
return new ViewHolder(itemView);
}
//replaces the contents of the main task view (invoked by the layout manager)
#Override
public void onBindViewHolder(ViewHolder holder, int position)
{
MainTasks obj = maintasklist.get(position); //MainTasks class obj called 'obj', which allows access to the MainTasks class
//obtains the main task and additional notes from the MainTask class
holder.maintask.setText(obj.getMainTasks());
holder.addnotes.setText(obj.getAdditionalNotes());
}
//returns the size of the main task list (invoked by the layout manager)
#Override
public int getItemCount()
{
return maintasklist.size();
}
}
AddNewMainTask.java (adds the tasks and additional notes to the RecyclerView)
package com.ricstudios.daymanager;
import android.support.v7.app.AppCompatActivity;
import android.content.Intent;
import android.os.Bundle;
import android.support.v7.widget.DefaultItemAnimator;
import android.support.v7.widget.LinearLayoutManager;
import android.support.v7.widget.RecyclerView;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.TextView;
import android.widget.EditText;
import android.widget.Button;
import android.view.View;
import java.util.ArrayList;
import java.util.List;
/*This class handles the window for adding new main tasks to the main task list (this window is the add_new_main_task_window.xml layout)*/
public class AddNewMainTask extends AppCompatActivity
{
private Button addbutton; //Button element from the add_new_main_task_window.xml layout
private EditText maintask, addnotes; //EditText elements from the add_new_main_task_window.xml layout
private List<MainTasks> maintasklist = new ArrayList<>();
private RecyclerView ListofMainTasks; //RecyclerView list element from the add_new_main_task_window.xml layout (containing the Main Task list)
private MainTaskAdapter TAdapter; //MainTaskAdapter class object 'TAdapter', allows access to the MainTaskAdapter class
/*sendButton method from the Button element in the add_new_main_task_window.xml and adds the main task and additional notes to the RecyclerView main task list*/
public void sendButton(View view)
{
maintask = (EditText)view.findViewById(R.id.maintasks);
addnotes = (EditText)view.findViewById(R.id.notes);
ListofMainTasks = (RecyclerView)findViewById(R.id.MainTaskList);
TAdapter = new MainTaskAdapter(maintasklist);
RecyclerView.LayoutManager mLayoutManager = new LinearLayoutManager(getApplicationContext());
ListofMainTasks.setLayoutManager(mLayoutManager);
ListofMainTasks.setItemAnimator(new DefaultItemAnimator());
ListofMainTasks.setAdapter(TAdapter);
/*Passes the EditText element values into the MainTask.java parameters*/
MainTasks mnt = new MainTasks(maintask.getText().toString(), addnotes.getText().toString());
maintasklist.add(mnt);
}
#Override
protected void onCreate(Bundle savedInstanceState)
{
super.onCreate(savedInstanceState);
setContentView(R.layout.add_new_main_task_window); //displays the window that allows users to add new main tasks (which is the add_new_main_task_window.xml layout)
addbutton = (Button)findViewById(R.id.addButton);
/*When user clicks button, the values the user puts in the EditText fields will be added to the RecyclerView list of the main_task_window.xml layout*/
addbutton.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v)
{
sendButton(v);
}
});
}
}
Whenever I press the "Add to Main Task" button, the app suddenly stop. Please help. Oh, and about the floatingactionbutton in the main_task_window.xml, don't worry about that. That just sends the user to the add_new_main_task_window.xml
Update: 3/5/19
I'm getting this error from the logcat:
03-05 15:22:49.298 10335-10335/com.project.daymanager E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.project.daymanager, PID: 10335
java.lang.NullPointerException: Attempt to invoke virtual method 'void android.support.v7.widget.RecyclerView.setLayoutManager(android.support.v7.widget.RecyclerView$LayoutManager)' on a null object reference
at com.project.daymanager.AddNewMainTask.sendButton(AddNewMainTask.java:39)
at com.project.daymanager.AddNewMainTask$1.onClick(AddNewMainTask.java:63)
at android.view.View.performClick(View.java:5702)
at android.widget.TextView.performClick(TextView.java:10887)
at android.view.View$PerformClick.run(View.java:22541)
at android.os.Handler.handleCallback(Handler.java:739)
at android.os.Handler.dispatchMessage(Handler.java:95)
at android.os.Looper.loop(Looper.java:158)
at android.app.ActivityThread.main(ActivityThread.java:7229)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1230)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1120)

Replace
view.findViewById();
with
findViewById();
In the MainTasks.java Don't use a constructor
public MainTasks(String mt, String an)
Just keep the set And get methods and do
MainTasks mt = new MainTasks();
mt.setMainTasks("Title");
mt.setAdditionalNotes("Note");
list.add(mt);
If it still not working, please post the error log so we can know whats the error.
Update: 3/5/19
You are trying to access the recyclerView of the MainTaskActivity in
ListofMainTasks = (RecyclerView)findViewById(R.id.MainTaskList);
from out side the activity (From another Activity) and that's not possible this way,
you can set the RecyclerView in the MainTaskActivity to static and use it in AddNewMainTask Activity by calling it
MainTaskActivity.myRecyclerView.

Problem is in this line:
ListofMainTasks = (RecyclerView)findViewById(R.id.MainTaskList);
program is unable to find recycler view and its null. and you can't set layout manager to a null object. I've reviewed your code and thing you did wrong is that in you onCreate method you are setting layout setContentView(R.layout.add_new_main_task_window); and you're trying to find recylerview which is not in this layout.
Your recycler view is in main_task_window.xml. use setContentView(R.layout.main_task_window.xml); and your activity will find recyclerview easily.
Note: if you want button/controls also which are in this layout add_new_main_task_window.xml then please move them in layout with recyclerview.

Related

How to keep scrolling position in ScrollView after rotating the screen in fragment with LiveDate object loaded

I have a fragment which is to display a lyrics of a song which is loaded from room databse based on its given id.
I'd like to preserve scrolling position after rotating the screen. Now after rotating the song is loaded again from db and the view is on the very top regardless of the scrolling position befor the rotating.
I thought that I can save scrolling position in onSaveInstanceState some bundle in onCreateView() use command on mSongDisplayScrollView.scrollTo(x, y)
The fragment code:
public class SongDisplayFragment extends Fragment {
private Song mSongToDisplay;
private ScrollView mSongDisplayScrollView;
private TextView mSongTitleTextView;
private RecyclerView mSongLyricsRecyclerView;
private GuitarSongbookViewModel mGuitarSongbookViewModel;
public static final String SONG_ID_KEY = "SONG_ID_KEY";
public SongDisplayFragment() {
}
public static SongDisplayFragment newInstance(Long songId) {
SongDisplayFragment songDisplayFragment = new SongDisplayFragment();
Bundle arguments = new Bundle();
arguments.putLong(SONG_ID_KEY,
songDisplayFragment.setArguments(arguments);
return songDisplayFragment;
}
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setHasOptionsMenu(false);
}
#Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
// Inflate the layout for this fragment
View view = inflater.inflate(R.layout.fragment_song_display, container, false);
mSongDisplayScrollView = view.findViewById(R.id.song_display_scroll_view);
mSongLyricsRecyclerView = view.findViewById(R.id.lyrics_rv_);
mSongTitleTextView = view.findViewById(R.id.
mGuitarSongbookViewModel = ViewModelProviders.of(this).get(GuitarSongbookViewModel.class);
final SongDisplayAdapter songDisplayAdapter = new SongDisplayAdapter(getContext());
Long songId = null;
if (getArguments().containsKey(SONG_ID_KEY)) {
songId = getArguments().getLong(SONG_ID_KEY);
}
if (songId != null) {
final Long finalSongId = songId;
mGuitarSongbookViewModel.getSongById(songId).observe(this, new Observer<Song>() {
#Override
public void onChanged(#Nullable final Song song) {
mSongToDisplay = song;
mSongTitleTextView.setText(mSongToDisplay.getMTitle());
songDisplayAdapter.setSong(song);
}
});
}
mSongLyricsRecyclerView.setAdapter(songDisplayAdapter);
mSongLyricsRecyclerView.setLayoutManager(new LinearLayoutManager(getContext()));
return view;
}
}
The fragment XML:
<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
xmlns:app="http://schemas.android.com/apk/res-auto"
android:layout_width="match_parent"
android:layout_height="match_parent"
tools:context=".fragments.SongDisplayFragment">
<ScrollView
android:id="#+id/song_display_scroll_view"
android:layout_width="match_parent"
android:layout_height="0dp"
app:layout_constraintBottom_toTopOf="#+id/autoscroll_bar"
app:layout_constraintTop_toTopOf="parent"
app:layout_constraintVertical_bias="1.0"
tools:layout_editor_absoluteX="138dp">
<LinearLayout
android:id="#+id/son_display_linear_layout"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:orientation="vertical">
<TextView
android:id="#+id/displayed_song_title_txt_"
style="#style/TitleOfDisplayedSong"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_marginStart="16dp"
android:layout_marginTop="8dp"
android:text="#string/title_placeholder" />
<androidx.recyclerview.widget.RecyclerView
android:id="#+id/lyrics_rv_"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:layout_marginTop="8dp"
android:layout_marginBottom="12dp"
android:nestedScrollingEnabled="false" />
</LinearLayout>
</ScrollView>
</androidx.constraintlayout.widget.ConstraintLayout>
The fragment displays a tiltle and lyrics of a song in a textView and RecyclerView which adapter class code is:
package com.example.guitarsongbook.adapters;
import android.content.Context;
import android.graphics.Rect;
import android.text.Html;
import android.util.TypedValue;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.TextView;
import androidx.annotation.NonNull;
import androidx.recyclerview.widget.GridLayoutManager;
import androidx.recyclerview.widget.RecyclerView;
import com.example.guitarsongbook.R;
import com.example.guitarsongbook.daos.SongChordJoinDao;
import com.example.guitarsongbook.model.Chord;
import com.example.guitarsongbook.model.Song;
import java.util.ArrayList;
import java.util.List;
public class SongDisplayAdapter extends RecyclerView.Adapter<SongDisplayAdapter.SongViewHolder> {
private Context context;
private final LayoutInflater mInflater;
private Song mSong;
private ArrayList<String> mLyrics;
public SongDisplayAdapter(Context context) {
this.context = context;
mInflater = LayoutInflater.from(context);
}
#NonNull
#Override
public SongViewHolder onCreateViewHolder(#NonNull ViewGroup parent, int viewType) {
View itemView = mInflater.inflate(R.layout.song_lyrics_rv_item, parent, false);
return new SongDisplayAdapter.SongViewHolder(itemView);
}
public void setSong(Song song){
mSong = song;
mLyrics = mSong.getMLyrics();
notifyDataSetChanged();
}
#Override
public void onBindViewHolder(#NonNull SongViewHolder holder, int position) {
holder.bindTo(position);
}
#Override
public int getItemCount() {
if (mLyrics != null)
return mLyrics.size();
else return 0;
}
public class SongViewHolder extends RecyclerView.ViewHolder {
private final TextView mLyricsLineTextView;
public SongViewHolder(#NonNull View itemView) {
super(itemView);
mLyricsLineTextView = itemView.findViewById(R.id.song_lyric_line_txt_);
}
public void bindTo(int position) {
if (mSong != null) {
mLyricsLineTextView.setText(Html.fromHtml(mLyrics.get(position)));
} else {
mLyricsLineTextView.setText(context.getString(R.string.no_song_label));
}
}
}
}
RecyclerView item XML:
<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="wrap_content">
<TextView
android:id="#+id/song_lyric_line_txt_"
style="#style/LyricOfDisplayedSong"
android:layout_width="0dp"
android:layout_height="wrap_content"
android:layout_marginStart="16dp"
android:layout_marginTop="4dp"
android:layout_marginEnd="24dp"
app:layout_constraintEnd_toStartOf="#+id/song_chord_line_txt_"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toTopOf="parent"
tools:text="placeholder text" />
</androidx.constraintlayout.widget.ConstraintLayout>
I think that the problem is that after rotating the screen song has to be loaded again by observer's methon onChange() so there is a short moment that there is nothing to display for scrollView. I'd like to find some solution how to return to the old position after again loading the song.

The first step is to persist the values of the objects through your Fragment's onSaveInstanceState method.
More of my explanations would come from the comments within each code block, so you can understand better on how it all works.
Values to be persisted: mSongToDisplay and mScrollViewPosition
//new variable introduced
int mScrollViewPosition = 0;
#Override
protected void onSaveInstanceState(Bundle outState) {
//If screen orientation changes, android redraws all views
//and non persistent data would be lost.
//Nevertheless, before this happens android informs the app via this method
//So to prevent state loss we save the data to a temporary storage
outState.putParcelable("song_data", mSongToDisplay);
//save ScrollView current position
outState.putInt("position_data", mSongDisplayScrollView.getScrollY());
//call super to commit your changes
super.onSaveInstanceState(outState);
}
Next is to recover the data after orientation change is completed
Add the following block in your fragments onCreateView and make sure the if statement block comes after initializing your adapter
...
//...add adapter initialization block here before checking for saved data
//Check for saved data
if (savedInstanceState != null) {
// Retrieve the data you saved
mSongToDisplay = savedInstanceState.getParcelable("song_data");
mScrollViewPosition = savedInstanceState.getInt("position_data");
//Re-initialize and reload adapter record
mSongToDisplay = song;
mSongTitleTextView.setText(mSongToDisplay.getMTitle());
songDisplayAdapter.setSong(song);
}
else {
//No data to retrieve
//initialize data model here.
}
//Assign the adapter to recyclerView
mSongLyricsRecyclerView.setAdapter(songDisplayAdapter);
mSongLyricsRecyclerView.setLayoutManager(new LinearLayoutManager(getContext()));
try{
//Finally we set the scrollview position at this point just to make sure
//recyclerview has its data loaded and full length of scrollview is restored
mSongDisplayScrollView.setScrollY(mScrollViewPosition);}
catch(Exception ex){
//position isn't right
}
return view;
At this point the required data has been persisted and on every screenOrientationChange the app would load the previously saved song object into the adapter preventing a false call to the db or api, and would also scroll to the expected position using the saved integer value mScrollViewPosition.

My app stopped every time when I load it

EDIT Happy New Year! To be precise ,I created a simple music app in Android Studio who read mp3 files from my internal storage. All good until I decide to put one random image on every single track on the list. (In front of the name of the song I want to appear one image).When I select one single image in 'src' at ImageView ,it works and appear to all songs. I will atach a part of my code below: Main Activity:
package com.alg.amzar.spectrum;
import android.content.ContentResolver;
import android.database.Cursor;
import android.net.Uri;
import android.os.Bundle;
import android.support.v7.app.AppCompatActivity;
import android.widget.ImageView;
import android.widget.ListView;
import java.util.ArrayList;
import java.util.Collections;
import java.util.Comparator;
import java.util.Random;
public class MainActivity extends AppCompatActivity {
static {
System.loadLibrary("native-lib");
}
private ArrayList<Song> songList;
private ListView songView;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
schimbare();
songView = (ListView)findViewById(R.id.song_list);
songList = new ArrayList<Song>();
getSongList();
Collections.sort(songList, new Comparator<Song>(){
public int compare(Song a, Song b){
return a.getTitle().compareTo(b.getTitle());
}
});
SongAdapter songAdt = new SongAdapter(this, songList);
songView.setAdapter(songAdt);
}
public void schimbare() {
int[] photos={R.drawable.img_0, R.drawable.img_1,R.drawable.img_2};
ImageView image = (ImageView) findViewById(R.id.imagine);
Random ran=new Random();
int i=ran.nextInt(photos.length);
image.setImageResource(photos[i]);
}
public void getSongList() {
ContentResolver musicResolver = getContentResolver();
Uri musicUri = android.provider.MediaStore.Audio.Media.EXTERNAL_CONTENT_URI;
Cursor musicCursor = musicResolver.query(musicUri, null, null, null, null);
if(musicCursor!=null && musicCursor.moveToFirst()){
//get columns
int titleColumn = musicCursor.getColumnIndex
(android.provider.MediaStore.Audio.Media.TITLE);
int idColumn = musicCursor.getColumnIndex
(android.provider.MediaStore.Audio.Media._ID);
//add songs to list
do {
long thisId = musicCursor.getLong(idColumn);
String thisTitle = musicCursor.getString(titleColumn);
songList.add(new Song(thisId, thisTitle));
}
while (musicCursor.moveToNext());
}
}
public native String stringFromJNI();
}
Activity Main .xml:
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
android:orientation="vertical"
android:background="#FF330000"
tools:context=".MainActivity" >
<ListView
android:id="#+id/song_list"
android:layout_width="fill_parent"
android:layout_height="wrap_content">
</ListView>
</LinearLayout>
Song.xml :
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:onClick="songPicked"
android:orientation="vertical"
android:padding="5dp" >
<ImageView
android:layout_width="70dp"
android:id="#+id/imagine"
android:layout_height="50dp" />
<TextView
android:id="#+id/song_title"
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:textColor="#FFFFFF99"
android:textSize="15sp"
android:textStyle="bold"
android:layout_marginBottom="20dp"
android:layout_marginLeft="75dp"
android:layout_marginTop="-42dp"/>
</LinearLayout>
Beside this ,I've 2 more java classes. I think the problem is here ,but idk what is wrong:
public void schimbare() {
int[] photos={R.drawable.img_0, R.drawable.img_1,R.drawable.img_2};
ImageView image = (ImageView) findViewById(R.id.imagine);
Random ran=new Random();
int i=ran.nextInt(photos.length);
image.setImageResource(photos[i]);
}
Another wondering of mine is what 'deprecated' means when is I use .getDrawable.
Thanks in advance!
Logcat:
ime: FATAL EXCEPTION: main
Process: com.alg.amzar.spectrum, PID: 28677
java.lang.RuntimeException: Unable to start activity ComponentInfo{com.alg.amzar.spectrum/com.alg.amzar.spectrum.MainActivity}: java.lang.NullPointerException
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2381)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2433)
at android.app.ActivityThread.access$800(ActivityThread.java:155)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1346)
at android.os.Handler.dispatchMessage(Handler.java:110)
at android.os.Looper.loop(Looper.java:193)
at android.app.ActivityThread.main(ActivityThread.java:5341)
at java.lang.reflect.Method.invokeNative(Native Method)
at java.lang.reflect.Method.invoke(Method.java:515)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:830)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:646)
at dalvik.system.NativeStart.main(Native Method)
Caused by: java.lang.NullPointerException
at com.alg.amzar.spectrum.MainActivity.schimbare(MainActivity.java:57)
at com.alg.amzar.spectrum.MainActivity.onCreate(MainActivity.java:31)
at android.app.Activity.performCreate(Activity.java:5343)
at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1088)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2335)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2433) 
at android.app.ActivityThread.access$800(ActivityThread.java:155) 
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1346) 
at android.os.Handler.dispatchMessage(Handler.java:110) 
at android.os.Looper.loop(Looper.java:193) 
at android.app.ActivityThread.main(ActivityThread.java:5341) 
at java.lang.reflect.Method.invokeNative(Native Method) 
at java.lang.reflect.Method.invoke(Method.java:515) 
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:830) 
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:646) 
at dalvik.system.NativeStart.main(Native Method) 
My phone android version: 4.4.2 (API 19)
Target SDK Version:"19"
MinSDK Version:"14"
SongAdapter.java:
package com.alg.amzar.spectrum;
import android.content.Context;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.BaseAdapter;
import android.widget.LinearLayout;
import android.widget.TextView;
import java.util.ArrayList;
public class SongAdapter extends BaseAdapter {
private ArrayList<Song> songs;
private LayoutInflater songInf;
public SongAdapter(Context c, ArrayList<Song> theSongs) {
songs = theSongs;
songInf = LayoutInflater.from(c);
}
#Override
public int getCount() {
return songs.size();
}
#Override
public Object getItem(int arg0) {
// TODO Auto-generated method stub
return null;
}
#Override
public long getItemId(int arg0) {
// TODO Auto-generated method stub
return 0;
}
#Override
public View getView(int position, View convertView, ViewGroup parent) {
//map to song layout
LinearLayout songLay = (LinearLayout)songInf.inflate
(R.layout.song, parent, false);
//get title and artist views
TextView songView = (TextView)songLay.findViewById(R.id.song_title);
//get song using position
Song currSong = songs.get(position);
//get title and artist strings
songView.setText(currSong.getTitle());
//set position as tag
songLay.setTag(position);
return songLay;
}
}

In your case, findViewById(R.id.imagine) returns NULL because it doesn't exist in the layout 'activity_main', which you provided in setContentView(). findViewById() returns NULL if the view doesn't exist in current layout. R.id.imagine exists in the layout song.xml.
I think, you are trying to inflate the ListView with layout 'song'. Only after inflating you can call findViewById and setImageResource. You can done it in class SongAdapter, for each elements in ListView after inflating them.
Another suggestion, instead of using random images you can get album art of a song from MediaMetadataRetriever class. You can refer android documentation for that. But you have to solve this exception before.
Comment/ Delete function schimbare() in onCreate and edit SongAdapter like following.
package com.alg.amzar.spectrum;
import android.content.Context;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.BaseAdapter;
import android.widget.LinearLayout;
import android.widget.TextView;
import java.util.ArrayList;
public class SongAdapter extends BaseAdapter {
private ArrayList<Song> songs;
private LayoutInflater songInf;
int[] photos={R.drawable.img_0, R.drawable.img_1,R.drawable.img_2};
Random ran=new Random();
// CHECK THIS:
public SongAdapter(Context c, ArrayList<Song> theSongs) {
songs = theSongs;
// CHECK THIS:
songInf = ( LayoutInflater )c.
getSystemService(Context.LAYOUT_INFLATER_SERVICE);
}
#Override
public int getCount() {
return songs.size();
}
#Override
public Object getItem(int arg0) {
// TODO Auto-generated method stub
return null;
}
#Override
public long getItemId(int arg0) {
// TODO Auto-generated method stub
return 0;
}
#Override
public View getView(int position, View convertView, ViewGroup parent) {
//map to song layout
LinearLayout songLay = (LinearLayout)songInf.inflate
(R.layout.song, null);
//get title and artist views
TextView songView = (TextView)songLay.findViewById(R.id.song_title);
// CHECK THIS:
ImageView img = (ImageView)songLay.findViewById(R.id.imagine);
//get song using position
Song currSong = songs.get(position);
//get title and artist strings
songView.setText(currSong.getTitle());
// CHECK THIS:
int i=ran.nextInt(photos.length);
img.setImageResource(photos[i]);
//set position as tag
songLay.setTag(position);
return songLay;
}
}

Deprecated mean that google no longer support this method, they telling you there is NEWER method you should use. the deprecated method is working fine FOR NOW. But some day (maybe tomorrow maybe 3 years from today) it will no longer work.
about the error, upload the log please.
The error is at line 57:
at com.alg.amzar.spectrum.MainActivity.schimbare(MainActivity.java:57)
I am not sure where line 57 is but you can check it in your code, if you still cant find the cause then update us which line is 57
public void schimbare() {
int[] photos={R.drawable.img_0, R.drawable.img_1,R.drawable.img_2};
ImageView image = (ImageView) findViewById(R.id.imagine);
Random ran=new Random();
// CHANGE photos.length to photos.length-1
int i=ran.nextInt(photos.length);
//ADD this 2 line of code below, then you can check in your Log if the problem is with the view (the view is null), or if the photos position is null.
Log.d("bug_tag",String.valueOf(photos[i]));
Log.d("bug_tag",String.valueOf(image.getId()));
image.setImageResource(photos[i]);
}

How to destroy and recreate objects in Android during runtime?

I'm developing an Android app that has to simulate a sort of Pokédex.
For now, what I want to do is simply have all 151 Pokémon printed on my device, so I can scroll them up and down.
The problem is that when I try this thing with such as 9 or 12 images there are no problems, but when I load all the 151 images (all .png), Android kills the app because it's draining too much system resources.
I've heard that there are Java methods that can (don't know how) "destroy" an object when it goes out of the display and then recreate it when it returns in the screen. Anyway if you have different suggestions on how to resolve my problem, every idea is welcome!
Here is my MainActivity:
package com.example.thefe.newsmartkedex;
import android.media.AudioManager;
import android.media.SoundPool;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;
import android.widget.AdapterView;
import android.widget.GridView;
import android.widget.Toast;
public class MainActivity extends AppCompatActivity {
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
GridView gridview = (GridView) findViewById(R.id.gridview);
gridview.setAdapter(new ImageAdapter(this));
gridview.setOnItemClickListener(new AdapterView.OnItemClickListener() {
public void onItemClick(AdapterView<?> parent, View v,
int position, long id) {
Toast.makeText(MainActivity.this, "" + position,
Toast.LENGTH_SHORT).show();
}
});
};
}
And here is my ImageAdapter class I use for Gridview:
package com.example.thefe.newsmartkedex;
import android.content.Context;
import android.view.View;
import android.view.ViewGroup;
import android.widget.BaseAdapter;
import android.widget.GridView;
import android.widget.ImageView;
public class ImageAdapter extends BaseAdapter {
private Context mContext;
public ImageAdapter(Context c) {
mContext = c;
}
public int getCount() {
return mThumbIds.length;
}
public Object getItem(int position) {
return null;
}
public long getItemId(int position) {
return 0;
}
// create a new ImageView for each item referenced by the Adapter
public View getView(int position, View convertView, ViewGroup parent) {
ImageView imageView;
if (convertView == null) {
// if it's not recycled, initialize some attributes
imageView = new ImageView(mContext);
imageView.setLayoutParams(new GridView.LayoutParams(200, 200));
imageView.setScaleType(ImageView.ScaleType.CENTER_CROP);
imageView.setPadding(8, 8, 8, 8);
} else {
imageView = (ImageView) convertView;
}
imageView.setImageResource(mThumbIds[position]);
return imageView;
}
// references to our images
private Integer[] mThumbIds = {
R.drawable.pkmn1, R.drawable.pkmn2,
R.drawable.pkmn3, R.drawable.pkmn4,
R.drawable.pkmn5, R.drawable.pkmn6,
R.drawable.pkmn7, R.drawable.pkmn8,
R.drawable.pkmn9, R.drawable.pkmn10,
R.drawable.pkmn11, R.drawable.pkmn12,
R.drawable.pkmn13, R.drawable.pkmn14,
R.drawable.pkmn15, R.drawable.pkmn16,
R.drawable.pkmn17, R.drawable.pkmn18,
R.drawable.pkmn19, R.drawable.pkmn20,
R.drawable.pkmn21, R.drawable.pkmn22,
R.drawable.pkmn23, R.drawable.pkmn24,
R.drawable.pkmn25, R.drawable.pkmn26,
R.drawable.pkmn27, R.drawable.pkmn28,
R.drawable.pkmn29, R.drawable.pkmn30,
R.drawable.pkmn31, R.drawable.pkmn32,
R.drawable.pkmn33, R.drawable.pkmn34,
R.drawable.pkmn35, R.drawable.pkmn36,
R.drawable.pkmn37, R.drawable.pkmn38,
R.drawable.pkmn39, R.drawable.pkmn40,
R.drawable.pkmn41, R.drawable.pkmn42,
R.drawable.pkmn43, R.drawable.pkmn44,
R.drawable.pkmn45, R.drawable.pkmn46,
R.drawable.pkmn47, R.drawable.pkmn48,
R.drawable.pkmn49, R.drawable.pkmn50,
R.drawable.pkmn51, R.drawable.pkmn52,
R.drawable.pkmn53, R.drawable.pkmn54,
R.drawable.pkmn55, R.drawable.pkmn56,
R.drawable.pkmn57, R.drawable.pkmn58,
R.drawable.pkmn59, R.drawable.pkmn60,
R.drawable.pkmn61, R.drawable.pkmn62,
R.drawable.pkmn63, R.drawable.pkmn64,
R.drawable.pkmn65, R.drawable.pkmn66,
R.drawable.pkmn67, R.drawable.pkmn68,
R.drawable.pkmn69, R.drawable.pkmn70,
R.drawable.pkmn71, R.drawable.pkmn72,
R.drawable.pkmn73, R.drawable.pkmn74,
R.drawable.pkmn75, R.drawable.pkmn76,
R.drawable.pkmn77, R.drawable.pkmn78,
R.drawable.pkmn79, R.drawable.pkmn80,
R.drawable.pkmn81, R.drawable.pkmn82,
R.drawable.pkmn83, R.drawable.pkmn84,
R.drawable.pkmn85, R.drawable.pkmn86,
R.drawable.pkmn87, R.drawable.pkmn88,
R.drawable.pkmn89, R.drawable.pkmn90,
R.drawable.pkmn91, R.drawable.pkmn92,
R.drawable.pkmn93, R.drawable.pkmn94,
R.drawable.pkmn95, R.drawable.pkmn96,
R.drawable.pkmn97, R.drawable.pkmn98,
R.drawable.pkmn99, R.drawable.pkmn100,
R.drawable.pkmn101, R.drawable.pkmn102,
R.drawable.pkmn103, R.drawable.pkmn104,
R.drawable.pkmn105, R.drawable.pkmn106,
R.drawable.pkmn107, R.drawable.pkmn108,
R.drawable.pkmn109, R.drawable.pkmn110,
R.drawable.pkmn111, R.drawable.pkmn112,
R.drawable.pkmn113, R.drawable.pkmn114,
R.drawable.pkmn115, R.drawable.pkmn116,
R.drawable.pkmn117, R.drawable.pkmn118,
R.drawable.pkmn119, R.drawable.pkmn120,
R.drawable.pkmn121, R.drawable.pkmn122,
R.drawable.pkmn123, R.drawable.pkmn124,
R.drawable.pkmn125, R.drawable.pkmn126,
R.drawable.pkmn127, R.drawable.pkmn128,
R.drawable.pkmn129, R.drawable.pkmn130,
R.drawable.pkmn131, R.drawable.pkmn132,
R.drawable.pkmn133, R.drawable.pkmn134,
R.drawable.pkmn135, R.drawable.pkmn136,
R.drawable.pkmn137, R.drawable.pkmn138,
R.drawable.pkmn139, R.drawable.pkmn140,
R.drawable.pkmn141, R.drawable.pkmn142,
R.drawable.pkmn143, R.drawable.pkmn144,
R.drawable.pkmn145, R.drawable.pkmn146,
R.drawable.pkmn147, R.drawable.pkmn148,
R.drawable.pkmn149, R.drawable.pkmn150,
R.drawable.pkmn151
};
}
Finally, this is the XML file
<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:id="#+id/activity_main"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:paddingBottom="#dimen/activity_vertical_margin"
android:paddingLeft="#dimen/activity_horizontal_margin"
android:paddingRight="#dimen/activity_horizontal_margin"
android:paddingTop="#dimen/activity_vertical_margin"
tools:context="com.example.thefe.newsmartkedex.MainActivity">
<GridView xmlns:android="http://schemas.android.com/apk/res/android"
android:id="#+id/gridview"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:columnWidth="90dp"
android:numColumns="auto_fit"
android:verticalSpacing="10dp"
android:horizontalSpacing="10dp"
android:stretchMode="columnWidth"
android:gravity="center"
/>
</RelativeLayout>
Thanks for help!

First of all, I don't see any violation in your code so let's focus the pictures.
The problem is that when I try this thing with such as 9 or 12 images there are no problems, but when I load all the 151 images (all .png), Android kills the app because it's draining too much system resources.
What do you mean by 'load all the 151 images'? At the same time in the same screen? Or you just make quite a small numbers of them(like 9,12,16 etc.) seen in the view and others out of the screen?
I've heard that there are Java methods that can (don't know how) "destroy" an object when it goes out of the display and then recreate it when it returns in the screen. Anyway if you have different suggestions on how to resolve my problem, every idea is welcome!
You can't simply destroy an object by yourself and the Jvm will handle this for you when your objects are invalid or unused. As to this problem the recreation of objects that you implements in 'getView' seems no harm.
My question is: how many images did you show in one whole screen? And what size of them?
If you can provide your demo here, it will be the best to work on.

Display limited images that can fit your screen and load the other images when scrolling Gridview.
That way system wont have do to do lots of work at once. Your application gets faster also.
You can refer this link:
i want grid view with loading by scroll i have image fetch from sever but i want only 10 images view other can load when scrolling grid view

Unhandled exception type when trying to use buttons as Nav menu

I am trying to link different buttons to different activities. so in effect creating a navigation menu.
I am trying to use less code so am trying to create one function i can pass values to in order to dynamically identify the buttons id and give it a link to the activity.
Here is my xml:
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent" >
<Button
android:id="#+id/nav1"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_alignParentLeft="true"
android:layout_alignParentRight="true"
android:layout_alignParentTop="true"
android:text="#string/nav1" />
<Button
android:id="#+id/nav2"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_alignParentLeft="true"
android:layout_alignParentRight="true"
android:layout_below="#+id/nav1"
android:text="#string/nav2" />
</RelativeLayout>
Here is my Java:
package com.example.myfirstapp;
import android.app.Activity;
import android.content.Intent;
import android.os.Bundle;
import android.view.Menu;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;
public class Nav extends Activity {
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_nav);
String nav1 = "nav1";
String nav2 = "nav2";
String MainActivity = "MainActivity";
String SQLite = "SQLite";
navButton(nav1, MainActivity);
navButton(nav2, SQLite);
}
#Override
public boolean onCreateOptionsMenu(Menu menu) {
getMenuInflater().inflate(R.menu.activity_nav, menu);
return true;
}
private void navButton(String buttonId, String activityName){
String bId = buttonId;
final Class<?> aName = Class.forName(activityName);
int resId = getResources().getIdentifier(bId, "id", getPackageName());
Button b = (Button) findViewById(resId);
OnClickListener onClickListener = new OnClickListener(){
#Override
public void onClick(View v) {
Intent i = new Intent(Nav.this, aName);
startActivity(i);
}};
b.setOnClickListener(onClickListener);
}
}
I am getting an error on line:
final Class<?> aName = Class.forName(activityName);
And it says:
Unhandled exception type ClassNotFoundException
Or quite simply whats the best way to do this

Any time I use Class.forName I pass in a qualified name, e.g. "mypackage.myclass". I'm not sure if it works with an unqualified name.
In any case, why pass in the string and then do a forName? Why not change the signature to take a Class object and just pass in MainActivity.class, etc? Then you'd catch any missing classes or spelling errors at compile time instead of run time.
Update in response to comment
public class Nav extends Activity {
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_nav);
navButton("nav1", MainActivity.class);
navButton("nav2", SQLite.class);
}
#Override
public boolean onCreateOptionsMenu(Menu menu) {
getMenuInflater().inflate(R.menu.activity_nav, menu);
return true;
}
private void navButton(String buttonId, Class aName){
String bId = buttonId;
// aName now passed in so doesn't need to be looked up
... etc ...
}
}
I think the above should compile and run. I haven't tried it but I've done similar things. Depending on how your packages are set up, you may need to import MainActivity and SQLite, or fully quality them, in order to take the .class.

Have you defined your activities in your application's AndroidManifest.xml?

You aren't catching the checked exception ClassNotFoundException. You need to wrap the relevant code in a try/catch block, e.g.
try {
final Class<?> aName = Class.forName(activityName);
//etc...
} catch (ClassNotFoundException e) {
//Do whatever cleanup you have to do in case this situation occurs.
}
This seems like an unusually awkward way to set a click listener, though. Why can you not just pass in the class itself to your navButton method instead of doing reflection (which should always be a last resort if there's an alternative)?

What is the best way to instantiate widgets which are pre-defined in XML layouts in a custom View class?

I am rather new to Android programming in general and am having particular difficulty with the xml/java UI shuffle... I have a layout which I would like to use as the view displayed when a custom, view class is instantiated in the activity class. This much works fine by simply calling
setContentView(R.layout.mylayout) ;
in the activity or from the custom view class through a handle to the activity. The trouble comes when I wish to interact with the widgets on the layout-- I've tried getting a handle on the buttons with
myButton = (Button) findViewById(R.id.mybuttonid);
and separately with
Button myButton = new Button(contextHandle);
myButton = (Button) findViewById(R.layout.mybuttonid);
but in both cases whenever I try to call any methods from the assumed myButton object I get a NullPointerException in the logcat report; evidently myButton is not properly instantiated in either case given above. What is the proper way to instantiate components of a view in a case like this that combines xml and java so that they can call methods dynamically?
thanks,
CCJ
EDIT: Thanks all for the replies, but I think up to 8/1/2011 the advice has been mostly targeted at an implementation wherein the widgets are to be instantiated in the activity class; I wish to instantiate widgets from an xml layout in a custom view class-- a class completely separate from the activity class which extends View and implements its own OnClickListener interface. Below is my code:
MyActivity Class:
package com.ccg.myactivity;
import android.app.Activity;
import android.os.Bundle;
import android.util.Log;
import android.view.MotionEvent;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;
import android.widget.RadioButton;
public class MyActivity extends Activity implements OnClickListener {
private boolean touched = false;
private RadioButton myRB;
private Button runB;
private CustomView myView;
/** Called when the activity is first created. */
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.mainlayout);
myRB = (RadioButton) findViewById(R.id.testrb);
runB = (Button) findViewById(R.id.goButton);
//set onClick listeners for activity class
runB.setOnClickListener(this);
}
public void onResume(){
super.onResume();
}
public void onClick(View v) {
// do something when the button is clicked
if (myRB.isChecked()){
setContentView(R.layout.mylayout);
myView = new CustomView(this,this); //passing in activity and context
//handles to custom View class
//myView.getAnotherB().setOnClickListener(this); //commented out as we
//don't want to register the custom view's button with the Activty class's
//OnClickListener; instead it should be registered with the custom View class's own
//OnClickListener implementation.
}
else{
Log.d("me","alt click");
}
}
}
CustomView Class:
package com.ccg.myactivity;
import android.app.Activity;
import android.content.Context;
import android.util.Log;
import android.view.MotionEvent;
import android.view.View;
import android.view.ViewGroup;
import android.widget.*;
import android.view.View.OnClickListener;
public class CustomView extends View implements OnClickListener{
private Button anotherB;
private Context contextHandle;
private Activity actHandle;
public CustomView(Context context, Activity act) {
super(context);
contextHandle = context;
actHandle = act;
//anotherB = new Button(contextHandle); //this shouldn't be necessary for
//instantiation from XML widget
initCustomView();
}
public void initCustomView(){
anotherB = (Button) findViewById(R.id.nextbutton);
anotherB.setOnClickListener(this);
}
public Button getAnotherB(){
return anotherB;
}
#Override
public void onClick(View arg0) {
// TODO Auto-generated method stub
Log.d("me", "Got the custom click!");
}
}
mainlayout.xml from which the default view is made:
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout
android:id="#+id/widget474"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
xmlns:android="http://schemas.android.com/apk/res/android"
android:orientation="vertical">
<RadioGroup android:id="#+id/widget30" android:orientation="horizontal"
android:layout_x="2dip" android:layout_y="57dip" android:layout_width="match_parent"
android:layout_height="wrap_content">
<RadioButton android:layout_height="wrap_content" android:id="#+id/testrb"
android:textSize="15sp" android:text="Run" android:layout_width="wrap_content"
android:textColor="#ffff99ff"></RadioButton>
</RadioGroup>
<Button android:layout_width="wrap_content" android:text="#string/RUN"
android:id="#+id/goButton" android:layout_height="wrap_content"
android:layout_x="222dip" android:layout_y="110dip"></Button>
</LinearLayout>
mylayout.xml from which the custom view's layout is created:
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout
android:id="#+id/widget0"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
xmlns:android="http://schemas.android.com/apk/res/android"
android:orientation="vertical">
<Button android:id="#+id/nextbutton" android:layout_height="wrap_content"
android:layout_width="wrap_content" android:text="work!!!"
>
</Button>
</LinearLayout>
okay, if anybody can explain why any method calls from the button object anotherB (anotherB.setOnClickListener(this) above, but also the simpler anotherB.bringToFront()) cause a force close and a nullpointerexception in logcat with the above implementation I would be most appreciative. thanks!
CCJ

I would declare your button outside of onCreate without the contextHandle parameter... The context will be imbedded in your button upon instantiation (as I understand it).
try:
class YOUR_CLASS {
Button myButton;
onCreate() {
myButton = (Button) findViewById(R.id.WHATEVER_YOU_CALLED_IT_IN_XML);
then you can set an onClickListener or other abilities (you can google that, its easy)
myButton.setOnClickListener(myOnClickListener);
myButton.setText("click me!");
}
}

This sometimes happens to me when the import isn't correct. Sometimes Eclipse will fill in the import as:
import android.R;
of course, this will never find your ID. You should either not have an import, or have something like
import com.myco.mytestapp.R;
If you do that, then the first way of doing it is correct:
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.mylayout);
Button b = (Button) findViewById(R.id.mybutton);
}

Okay, thanks to some advice from the android developers google group I think I've found the answer to at least the most pressing concern (the NPE and force close):
I needed to override onFinishInflate in my custom View class; it is at that point that my XML layout child views (like anotherB) are truly instantiated. The class now looks like this
package com.ccg.myactivity;
import android.app.Activity;
import android.content.Context;
import android.util.Log;
import android.view.MotionEvent;
import android.view.View;
import android.view.ViewGroup;
import android.widget.*;
import android.view.View.OnClickListener;
public class CustomView extends View implements OnClickListener{
private Button anotherB;
private Context contextHandle;
private Activity actHandle;
public CustomView(Context context, Activity act) {
super(context);
contextHandle = context;
actHandle = act;
//anotherB = new Button(contextHandle); //this shouldn't be necessary for
//instantiation from XML widget
initCustomView();
}
public void initCustomView(){
anotherB = (Button) findViewById(R.id.nextbutton);
anotherB.setOnClickListener(this);
}
public Button getAnotherB(){
return anotherB;
}
#Override
public void onFinishInflate(){
anotherB.setOnClickListener(this); //it seems any addressing of child
//views of the layout [the widgets] need to be made after the
//framework calls this method.
}
#Override
public void onClick(View arg0) {
// TODO Auto-generated method stub
Log.d("me", "Got the custom click!");
}
}
Now it pulls up the layout properly and does not throw an NPE. Of course, the onClickListener callback still isn't working right (the message 'Got the custom click!' never appears in logcat), but that's another issue...
thanks all
CCJ

Okay, finally had some time to revisit this issue and I believe I've found the answer:
First, before the xml layout or its components can be addressed they need to be inflated. I knew this, but I wasn't sure when exactly they were inflated. It turns out that setContextView (and probably addContextView) trigger xml inflations. In order to have completely modular activity/view classes, I needed to do something like the following:
Activity Class--
package com.ai.ultimap;
import com.ai.ultimap.views.HomeView;
import android.app.Activity;
import android.os.Bundle;
import android.view.View;
import android.view.ViewGroup.LayoutParams;
public class UltiMapActivity extends Activity {
private View hv;
/** Called when the activity is first created. */
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
hv = new HomeView(this);
}
}
Custom View Class-
package com.ai.ultimap.views;
import com.ai.ultimap.R;
import android.app.Activity;
import android.os.Bundle;
import android.view.*;
import android.widget.*;
import android.view.View.OnClickListener;
public class HomeView extends View implements OnClickListener{
private RadioButton twodRB;
private RadioButton threedRB;
private TextView locTV;
private EditText editlocET;
public HomeView(Activity hAct) {
super(hAct);
//THE FOLLOWING LINE INFLATES-- IT (or another function which calls xml inflation)
//MUST COME BEFORE ANY JAVA ADDRESSING OF WIDGETS IN
//THE XML LAYOUT
//Also note that even though you could invoke findViewById from a class extending
//View, in this case you must use hAct.findViewById. I believe this is due to the
//fact that the activity referenced by hAct is the object responsible for inflating
//the xml and thus the widgets need to be instantiated from it.
hAct.setContentView(R.layout.ultimap);
twodRB = (RadioButton) hAct.findViewById(R.id.twodRBV);
threedRB = (RadioButton) hAct.findViewById(R.id.threedRBV);
locTV = (TextView) hAct.findViewById(R.id.locationTV);
editlocET = (EditText) hAct.findViewById(R.id.locationETV);
//After instantiation however they can be freely accessed from java in
//non-activity classes, which is the point; see the next line...
twodRB.setOnClickListener(this);
}
#Override
public void onClick(View v) {
// TODO Auto-generated method stub
locTV.setText("yo");
}
}
This code works properly to load up the pre-defined xml view ultimap.xml and then address the widgets dynamically from Java (completely outside the activity class), changing the text of the location text view from 'Location' to 'yo' when the twodRB radiobutton is clicked!
Hope this helps some googlers :)
-CCJ

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