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Referencing TextViews from Activity in Service and Vice versa

I am working on an Android app with a steadily growing Code basis; the aim of the app is to scan and process QR Codes and Barcodes on Handheld Devices for Storages (not Smartphones). It hast two Activities that contain major parts of the programmatical logic; hence, I want to store major parts of the Code that contains the Functionality for processing the Scanner input in an external Service, called Scanner Service, implement the methods there and use the methods in other Activites;
however, I have a major issue with the use of Context, getApplicationContext() and the reference of the Activity in the Service and vice versa; although I think I have referenced and initialised the Textviews from the Activity in the Service, the app keeps on crashing with the following error message:
AndroidRuntime: Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'android.view.View android.app.Activity.findViewById(int)' on a null object reference
at com.xxxx.ScanService.<clinit>(ScanService.java:16)
I know what it means, but I don´t know how I could access the View
private static TextView content = (TextView) a.findViewById(R.id.content_detail);
in such a way that I can use it in the Service and in the Activity and the app stops crashing.
Therefore, any hints or help would be very much appreciated, thank you in advance.
The MainDetailActivity:
package com.example.xxx_app;
import android.app.Activity;
import android.app.Dialog;
import android.content.Context;
import android.content.Intent;
import android.graphics.drawable.ColorDrawable;
import android.os.Bundle;
import android.util.Log;
import android.view.KeyEvent;
import android.view.Menu;
import android.view.View;
import androidx.appcompat.app.AppCompatActivity;
import androidx.appcompat.widget.Toolbar;
import androidx.recyclerview.widget.RecyclerView;
import android.view.MenuItem;
import android.view.Window;
import android.widget.AdapterView;
import android.widget.ArrayAdapter;
import android.widget.Button;
import android.widget.EditText;
import android.widget.ImageButton;
import android.widget.ImageView;
import android.widget.ListView;
import android.widget.PopupMenu;
import android.widget.Spinner;
import android.widget.TextView;
import android.widget.Toast;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import static com.xxx.ScanService.*;
import static com.xxx.SimpleItemRecyclerViewAdapter.TAGG;
/**
* An activity representing a single Main detail screen. This
* activity is only used on narrow width devices. On tablet-size devices,
* item details are presented side-by-side with a list of items
* in a {#link MainListActivity}.
*/
public class MainDetailActivity extends AppCompatActivity implements AdapterView.OnItemSelectedListener,
PopupMenu.OnMenuItemClickListener {
Context context;
private RecyclerView recyclerView;
private RecyclerviewAdapter recyclerviewAdapter;
private RecyclerTouchListener touchListener;
private ListView listView;
public TextView textView4;
public String code;
public static final String TAG = "Barcode ist:" ;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main_detail);
context = this;
//TextView headerView = findViewById(R.id.txt1);
Spinner spinner = (Spinner) findViewById(R.id.spinner);
EditText editBarcode = (EditText) findViewById(R.id.editText);
TextView content = (TextView) findViewById(R.id.content_detail);
TextView editTextNumber = findViewById(R.id.editTextNumber);
Button addBooking = findViewById(R.id.button);
Button removeBooking = findViewById(R.id.button2);
removeBooking.setEnabled(false);
spinner.setOnItemSelectedListener(this);
//String selectedItem = spinner.getSelectedItem().toString();
// Create an ArrayAdapter using the string array and a default spinner layout
ArrayAdapter<CharSequence> adapter = ArrayAdapter.createFromResource(this,
R.array.mockdata, android.R.layout.simple_spinner_item);
// Specify the layout to use when the list of choices appears
adapter.setDropDownViewResource(android.R.layout.simple_spinner_dropdown_item);
// Apply the adapter to the spinner
spinner.setAdapter(adapter);
String scannedCode = getIntent().getStringExtra("scannedCode");
Log.d(TAG, "scannedCode" + scannedCode);
if (scannedCode != null && (content.getText().toString().equals(""))) {
content.setText(scannedCode);
}
Button btn = findViewById(R.id.imageView4);
btn.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
PopupMenu popup = new PopupMenu(MainDetailActivity.this, v);
popup.setOnMenuItemClickListener(MainDetailActivity.this);
popup.inflate(R.menu.popup_menu);
popup.show();
}
});
editBarcode.setOnKeyListener(new View.OnKeyListener() {
#Override
public boolean onKey(View v, int keyCode, KeyEvent event) {
// TODO Auto-generated method stub
String code = editBarcode.getText().toString();
if (code.matches("")) //{ if(code.trim().isEmpty())
//|| editBarcode.getText().toString() > 100 )
{
Log.d(TAG, "Code ist leer");
}
if (keyCode == KeyEvent.KEYCODE_ENTER && code.length() > 0) {
editBarcode.setText("");
ScanService.checkEnteredCode(code);
return true;
}
return false;
}
});
recyclerView = findViewById(R.id.recyclerview);
recyclerviewAdapter = new RecyclerviewAdapter(this);
Intent newIntent = getIntent();
String receivedPalNo = newIntent.getStringExtra("palNo");
String receivedNo = newIntent.getStringExtra("no");
String receivedType = newIntent.getStringExtra("type");
String receivedRack = newIntent.getStringExtra("rack");
String receivedCountItems = newIntent.getStringExtra("count_items");
content.setText(receivedCountItems);
RestClient.getPaletteItems(getApplicationContext(),recyclerviewAdapter,receivedPalNo);
Log.d(TAGG,"Intent 1" + receivedPalNo);
Log.d(TAGG, "Intent 2" + receivedNo);
Log.d(TAGG, "Intent 3" + receivedType);
Log.d(TAGG,"Intent 4" + receivedRack);
Log.d(TAGG, "Intent 5" + receivedCountItems);
final ArrayList<Items> itemList = new ArrayList<>();
/*
Items[] items = new Items(12345,123456, 200, 500);
itemList.add(items);*/
recyclerviewAdapter.setItemList((ArrayList<Items>) itemList);
recyclerView.setAdapter(recyclerviewAdapter);
touchListener = new RecyclerTouchListener(this,recyclerView);
RecyclerviewAdapter finalRecyclerviewAdapter = recyclerviewAdapter;
touchListener
.setClickable(new RecyclerTouchListener.OnRowClickListener() {
#Override
public void onRowClicked(int position) {
//Toast.makeText(getApplicationContext(),itemList.get(position), Toast.LENGTH_SHORT).show();
}
#Override
public void onIndependentViewClicked(int independentViewID, int position) {
}
})
.setSwipeOptionViews(R.id.delete_task,R.id.edit_task)
.setSwipeable(R.id.rowFG, R.id.rowBG, new RecyclerTouchListener.OnSwipeOptionsClickListener() {
#Override
public void onSwipeOptionClicked(int viewID, int position) {
switch (viewID){
case R.id.delete_task:
itemList.remove(position);
finalRecyclerviewAdapter.setItemList(itemList);
break;
case R.id.edit_task:
Toast.makeText(getApplicationContext(),"Edit Not Available",Toast.LENGTH_SHORT).show();
break;
}
}
});
recyclerView.addOnItemTouchListener(touchListener);
class StableArrayAdapter extends ArrayAdapter<String> {
HashMap<String, Integer> mIdMap = new HashMap<String, Integer>();
public StableArrayAdapter(Context context, int textViewResourceId,
List<String> objects) {
super(context, textViewResourceId, objects);
for (int i = 0; i < objects.size(); ++i) {
mIdMap.put(objects.get(i), i);
}
}
#Override
public long getItemId(int position) {
String item = getItem(position);
return mIdMap.get(item);
}
#Override
public boolean hasStableIds() {
return true;
}
}
// savedInstanceState is non-null when there is fragment state
// saved from previous configurations of this activity
// (e.g. when rotating the screen from portrait to landscape).
// In this case, the fragment will automatically be re-added
// to its container so we don"t need to manually add it.
// For more information, see the Fragments API guide at:
//
// http://developer.android.com/guide/components/fragments.html
//
String text = getIntent().getStringExtra("palNo");
//headerView.setText(text);
if (receivedType != null && receivedType.equals("FE")) {
ImageView mImgView = findViewById(R.id.id_col_code);
mImgView.setBackgroundResource(R.drawable.backgroun_blue);
}
if (receivedType != null && receivedType.equals("UFE")) {
ImageView mImgView = findViewById(R.id.id_col_code);
mImgView.setBackgroundResource(R.drawable.backgroun_yellow);
}
}
public boolean onCreateOptionsMenu(Menu menu) {
// Inflate the menu; this adds items to the action bar if it is present.
getMenuInflater().inflate(R.menu.main, menu);
return true;
}
public boolean onMenuItemClick(MenuItem item) {
Toast.makeText(this, "Selected Item: " +item.getTitle(), Toast.LENGTH_SHORT).show();
switch (item.getItemId()) {
case R.id.search_item:
// do your code
return true;
case R.id.upload_item:
// do your code
return true;
case R.id.copy_item:
// do your code
return true;
/* case R.id.print_item:
// do your code
return true;*/
case R.id.share_item:
// do your code
return true;
/*case R.id.bookmark_item:
// do your code
return true;*/
default:
return false;
}
}
public void newDialog(Activity activity) {
final Dialog dialog = new Dialog(activity);
dialog.requestWindowFeature(Window.FEATURE_NO_TITLE);
dialog.setCancelable(true);
dialog.setContentView(R.layout.sortiment_layout);
dialog.getWindow().setBackgroundDrawable(new ColorDrawable(android.graphics.Color.TRANSPARENT));
Button okButton = dialog.findViewById(R.id.ok);
okButton.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
//Toast.makeText(getApplicationContext(),"Ok" ,Toast.LENGTH_SHORT).show();
dialog.dismiss();
}
});
Button cancelButton = dialog.findViewById(R.id.cancel);
cancelButton.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
//Toast.makeText(getApplicationContext(),"Abbrechen" ,Toast.LENGTH_SHORT).show();
dialog.cancel();
}
});
dialog.show();
}
public void showDialog(Activity activity) {
final Dialog dialog = new Dialog(activity);
dialog.requestWindowFeature(Window.FEATURE_NO_TITLE);
dialog.setCancelable(true);
dialog.setContentView(R.layout.newcustom_layout);
dialog.getWindow().setBackgroundDrawable(new ColorDrawable(android.graphics.Color.TRANSPARENT));
Button okButton = dialog.findViewById(R.id.ok);
okButton.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
//Toast.makeText(getApplicationContext(),"Ok" ,Toast.LENGTH_SHORT).show();
dialog.dismiss();
}
});
dialog.show();
}
public void onItemSelected(AdapterView<?> parent, View view,
int pos, long id) {
// An item was selected. You can retrieve the selected item using
// parent.getItemAtPosition(pos)
}
public void onNothingSelected(AdapterView<?> parent) {
// Another interface callback
}
#Override
public boolean onOptionsItemSelected(MenuItem item) {
int id = item.getItemId();
if (id == android.R.id.home) {
// This ID represents the Home or Up button. In the case of this
// activity, the Up button is shown. For
// more details, see the Navigation pattern on Android Design:
//
// http://developer.android.com/design/patterns/navigation.html#up-vs-back
//
navigateUpTo(new Intent(this, MainListActivity.class));
return true;
}
return super.onOptionsItemSelected(item);
}
#Override
public void onResume() {
super.onResume();
recyclerView.addOnItemTouchListener(touchListener);
}
#Override
public void onPointerCaptureChanged(boolean hasCapture) {
}
}
The ScanService Class:
package com.example.xxx;
import android.app.Activity;
import android.content.Context;
import android.util.Log;
import android.widget.TextView;
public class ScanService {
private static final String TAG = "Scan Service Tag";
private static Context mContext;
private static Activity a = (MainDetailActivity)mContext;
private static TextView content = (TextView)
a.findViewById(R.id.content_detail);
private static TextView editTextNumber = (TextView)
a.findViewById(R.id.editTextNumber);
public ScanService (Context mContext) {
this.mContext = mContext;
}
public static void checkEnteredCode(String code, Activity a) {
content.setText("");
//PSP-H1-EA-F3
if
(code.matches("PSP-\\p{Upper}\\d\\p{Punct}\\p{Upper}\\" +
"p{Upper}\\p{Punct}\\p{Upper}\\p{Digit}")) {
content.setText("");
content.setText(code);
Log.d(TAG, "xxx");
}
if (code.matches("LF-[0-9]*")) {
///LF-(\d+)/gi
content.setText("");
content.setText(code);
Log.d(TAG, "xxx");
}
if (code.matches("PAL-[0-9][0-9][0-9]")) {
content.setText("");
content.setText(code);
Log.d(TAG, "xxx");
}
if (code.matches("P-[0-9][0-9][0-9]")) {
content.setText("");
content.setText(code);
Log.d(TAG, "Palette");
}
if (code.matches("[0-9][0-9][0-9][0-9].[0-9][0-9].+DB")) {
if(editTextNumber == null) {
Log.d(TAG, "xxx");
}
else {
editTextNumber.setText(code);
Log.d(TAG, "xxx");
}
Log.d(TAG, "xxx");
}
if (code.matches("[0-9A-Z]*[0-9]*")) {
//editBarcode.setText("");
//editBarcode.setText(keyCode);
Log.d(TAG, "xxx");
}
if (code.matches("\\d{13}")) {
//newDialog(MainDetailActivity.this);
//editBarcode.setText("");
//editBarcode.setText(keyCode);
if(editTextNumber == null) {
Log.d(TAG, "xxx");
}
else {
editTextNumber.setText(code);
Log.d(TAG, "xxx");
}
Log.d(TAG, "xxx");
}
else {
Log.d(TAG, "xxx");
};
//editBarcode.setText("");
//editBarcode.setText(code);
/* String code = editBarcode.getText().toString();
if (code.matches("")) //{ if(code.trim().isEmpty())
//|| editBarcode.getText().toString() > 100 )
{
Log.d(TAG, "xxx");
}
//}
checkEnteredCode(code);
//editBarcode.setText("");
return Boolean.parseBoolean(code);*/
Log.d(TAG, code);
}
public static void checkEnteredCode(String code) {
}
}

You cannot access any Views from a Service! Views belong to the Activity. This is the wrong application architecture. A Service performs background processing (file I/O, network I/O, computation, etc.). The Activity is responsible for interacting with the user (inputs, display, etc.). If your Service wants to put data on the screen, you've broken the division of responsibilities. Your Service should simply notify your Activity (or any other component that is interested) when data has changed, and the Activity can then update the View itself. You can share data between the Service and your other components in a number of ways, including: event bus, publish/subscribe, shared preferences, broadcast Intents, SQLite database, etc.

Convert number text field to int (for use in a conditional statement)

So I am very new to Android studio. My problem is relatively simple, convert data from a text field into a integer. The goal of that int is to be used in a conditional statement. However I cannot seem to find an answer that works. This is where my code that i'm having problems with is.
public void saveMatchData (MenuItem item) {
//save button in my menu
//creates a toast to notify that it has been pressed
Toast toast = Toast.makeText(getApplicationContext(), "Save button pressed", Toast.LENGTH_SHORT);
toast.show();
// create an EditText for matchNumberInput
EditText matchNumberET = (EditText) findViewById(R.id.matchNumberInput);
//assign value of matchNumberET(Edit Text) to match number
EditText matchNumber = (EditText) matchNumberET.getText();
//attempted to assign to an int
int matchNumberValue = Integer.parseInt(matchNumber);
// error here^^^^^
//same as abover just tried a different way that i read online
EditText teamNumberDT = (EditText) findViewById(R.id.teamNumberInput);
int teamNumber = Integer.parseInt(teamNumberDT.getText().toString());
int i;
//i have an array for matchNumber values and teamNumber values
//they start empty and as of now still are
//
for (i = 0, i <= matchNumberArray.size(), i++);{
if (matchNumberValue == matchNumberArray.get(i)){
// error here^^^^^^^^^^^^^^^^^^^^^^^^^^^^
//I just want to compare the value of i position of the array with the data from textfield
//code to add matchNumber if not already there
}
//both of these different ways to do this give me errors
}
if (teamNumberArray.get(i) == teamNumber) {
//error here^^^^^^^^^^^^^^^^^^^^^^^^^^^^
//code to add teamNumber if not already there
}
Is it a problem with the conversion of the textField to an int or is it the way im using it? Or is it a problem with my array/s?
Here is all of my code. Sorry, it's very sloppy.`
package com.example.garre.frcscouting13;
import android.net.Uri;
import android.support.design.widget.TabLayout;
import android.support.v7.app.AppCompatActivity;
import android.support.v7.widget.Toolbar;
import android.support.v4.app.Fragment;
import android.support.v4.app.FragmentManager;
import android.support.v4.app.FragmentPagerAdapter;
import android.support.v4.view.ViewPager;
import android.os.Bundle;
import android.view.LayoutInflater;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.view.ViewGroup;
import android.widget.ArrayAdapter;
import android.widget.Button;
import android.widget.EditText;
import android.widget.TextView;
import android.widget.Toast;
import com.google.android.gms.appindexing.Action;
import com.google.android.gms.appindexing.AppIndex;
import com.google.android.gms.appindexing.Thing;
import com.google.android.gms.common.api.GoogleApiClient;
import java.util.ArrayList;
import java.util.List;
public class MainActivity extends AppCompatActivity {
List<String> matchNumberArray = new ArrayList<String>();
//String matchNumberArray[] = {};
ArrayAdapter matchNumberAdapter = new ArrayAdapter<String> (this, R.layout.previous_fragment, matchNumberArray);
List<String> teamNumberArray = new ArrayList<String>();
// String teamNumberArray[] = {};
ArrayAdapter teamNumberAdapter = new ArrayAdapter<String>(this, R.layout.previous_fragment, teamNumberArray);
private SectionsPagerAdapter mSectionsPagerAdapter;
private ViewPager mViewPager;
/**
* ATTENTION: This was auto-generated to implement the App Indexing API.
* See https://g.co/AppIndexing/AndroidStudio for more information.
*/
private GoogleApiClient client;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
setSupportActionBar(toolbar);
// Create the adapter that will return a fragment for each of the three
// primary sections of the activity.
mSectionsPagerAdapter = new SectionsPagerAdapter(getSupportFragmentManager());
// Set up the ViewPager with the sections adapter.
mViewPager = (ViewPager) findViewById(R.id.container);
mViewPager.setAdapter(mSectionsPagerAdapter);
TabLayout tabLayout = (TabLayout) findViewById(R.id.tabs);
tabLayout.setupWithViewPager(mViewPager);
// ATTENTION: This was auto-generated to implement the App Indexing API.
// See https://g.co/AppIndexing/AndroidStudio for more information.
client = new GoogleApiClient.Builder(this).addApi(AppIndex.API).build();
}
#Override
public boolean onCreateOptionsMenu(Menu menu) {
// Inflate the menu; this adds items to the action bar if it is present.
getMenuInflater().inflate(R.menu.menu_main, menu);
return true;
}
#Override
public boolean onOptionsItemSelected(MenuItem item) {
// Handle action bar item clicks here. The action bar will
// automatically handle clicks on the Home/Up button, so long
// as you specify a parent activity in AndroidManifest.xml. #Override
// Handle item selection
switch (item.getItemId()) {
case R.id.saveMenuItem:
return true;
case R.id.ScreenShotMenuItem:
return true;
default:
return super.onOptionsItemSelected(item);
}
}
public void openScreenshotToast(MenuItem item) {
Toast toast = Toast.makeText(getApplicationContext(), "Screenshot button pressed", Toast.LENGTH_SHORT);
toast.show();
}
public void saveMatchData (MenuItem item) {
//save button in my menu
//creates a toast to notify that it has been pressed
Toast toast = Toast.makeText(getApplicationContext(), "Save button pressed", Toast.LENGTH_SHORT);
toast.show();
// create an EditText for matchNumberInput
EditText matchNumberET = (EditText) findViewById(R.id.matchNumberInput);
//assign value of matchNumberET(Edit Text) to match number
EditText matchNumber = (EditText) matchNumberET.getText();
//attempted to assign to an int
int matchNumberValue = Integer.parseInt(matchNumber);
//same as abover just tried a different way that i read online
EditText teamNumberDT = (EditText) findViewById(R.id.teamNumberInput);
int teamNumber = Integer.parseInt(teamNumberDT.getText().toString());
int i;
//i have an array for matchNumber values and teamNumber values
//they start empty and as of now still are
//
for (i = 0, i <= matchNumberArray.size(), i++);{
if (matchNumberValue == matchNumberArray.get(i)){
//code to add matchNumber if not already there
}
//both of these different ways to do this give me errors
}
if (teamNumberArray.get(i) == teamNumber) {
//code to add teamNumber if not already there
}
}
/**
* ATTENTION: This was auto-generated to implement the App Indexing API.
* See https://g.co/AppIndexing/AndroidStudio for more information.
*/
public Action getIndexApiAction() {
Thing object = new Thing.Builder()
.setName("Main Page") // TODO: Define a title for the content shown.
// TODO: Make sure this auto-generated URL is correct.
.setUrl(Uri.parse("http://[ENTER-YOUR-URL-HERE]"))
.build();
return new Action.Builder(Action.TYPE_VIEW)
.setObject(object)
.setActionStatus(Action.STATUS_TYPE_COMPLETED)
.build();
}
#Override
public void onStart() {
super.onStart();
// ATTENTION: This was auto-generated to implement the App Indexing API.
// See https://g.co/AppIndexing/AndroidStudio for more information.
client.connect();
AppIndex.AppIndexApi.start(client, getIndexApiAction());
}
#Override
public void onStop() {
super.onStop();
// ATTENTION: This was auto-generated to implement the App Indexing API.
// See https://g.co/AppIndexing/AndroidStudio for more information.
AppIndex.AppIndexApi.end(client, getIndexApiAction());
client.disconnect();
}
/**
* A placeholder fragment containing a simple view.
*/
public static class PlaceholderFragment extends Fragment {
/**
* The fragment argument representing the section number for this
* fragment.
*/
private static final String ARG_SECTION_NUMBER = "section_number";
public PlaceholderFragment() {
}
/**
* Returns a new instance of this fragment for the given section
* number.
*/
public static PlaceholderFragment newInstance(int sectionNumber) {
PlaceholderFragment fragment = new PlaceholderFragment();
Bundle args = new Bundle();
args.putInt(ARG_SECTION_NUMBER, sectionNumber);
fragment.setArguments(args);
return fragment;
}
#Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
if (getArguments().getInt(ARG_SECTION_NUMBER) == 1) {
View rootView = inflater.inflate(R.layout.fieldmap_fragment, container, false);
return rootView;
} else if (getArguments().getInt(ARG_SECTION_NUMBER) == 2) {
View rootView = inflater.inflate(R.layout.datainput_fragment, container, false);
return rootView;
} else {
View rootView = inflater.inflate(R.layout.previous_fragment, container, false);
return rootView;
}
}
}
/**
* A {#link FragmentPagerAdapter} that returns a fragment corresponding to
* one of the sections/tabs/pages.
*/
public class SectionsPagerAdapter extends FragmentPagerAdapter {
public SectionsPagerAdapter(FragmentManager fm) {
super(fm);
}
#Override
public Fragment getItem(int position) {
// getItem is called to instantiate the fragment for the given page.
// Return a PlaceholderFragment (defined as a static inner class below).
return PlaceholderFragment.newInstance(position + 1);
}
#Override
public int getCount() {
// Show 3 total pages.
return 3;
}
#Override
public CharSequence getPageTitle(int position) {
switch (position) {
case 0:
return "FieldMap";
case 1:
return "Match Data";
case 2:
return "Previous";
}
return null;
}
}
}
`

Extract your EditText Value like:
EditText matchNumberET = (EditText) findViewById(R.id.matchNumberInput);
int matchNumberValue = Integer.parseInt(matchNumberET.getText().toString());
And as seeing your code, I couldn't find your Intention towards the App. Please go through few tutorials as provided on Google's official site.

I did that for teamNumber. And then did matchnumber different to show that I've tried some different ways. Niether of them work though.

Android: how to convert activities to fragments in order to use the navigation drawer correctly?

I'm developing an android application that currently displays a list of articles in the MainActivity and is working correctly, i want to make the application a little more sophisticated by adding a navigation drawer that contains the articles' categories and a "Home" button above them.
So i started a new project on Android Studio and i selected blank app with Navigation Drawer then i imported my previous app manually into this new project and i renamed my previous MainActivity to HomePage.java, because the MainActivity here is for the Navigation Drawer.
I made many researches and i think that i have to convert my activities into fragments in order to work with Navigation Drawer, but i don't know how.
This is the MainActivity.java:
import android.app.Activity;
import android.content.Intent;
import android.support.v7.app.ActionBarActivity;
import android.support.v7.app.ActionBar;
import android.support.v4.app.Fragment;
import android.support.v4.app.FragmentManager;
import android.os.Bundle;
import android.view.LayoutInflater;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.view.ViewGroup;
import android.support.v4.widget.DrawerLayout;
public class MainActivity extends ActionBarActivity
implements NavigationDrawerFragment.NavigationDrawerCallbacks {
/**
* Fragment managing the behaviors, interactions and presentation of the navigation drawer.
*/
private NavigationDrawerFragment mNavigationDrawerFragment;
/**
* Used to store the last screen title. For use in {#link #restoreActionBar()}.
*/
private CharSequence mTitle;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
mNavigationDrawerFragment = (NavigationDrawerFragment)
getSupportFragmentManager().findFragmentById(R.id.navigation_drawer);
mTitle = getTitle();
// Set up the drawer.
mNavigationDrawerFragment.setUp(
R.id.navigation_drawer,
(DrawerLayout) findViewById(R.id.drawer_layout));
}
#Override
public void onNavigationDrawerItemSelected(int position) {
// update the main content by replacing fragments
FragmentManager fragmentManager = getSupportFragmentManager();
fragmentManager.beginTransaction()
.replace(R.id.container, PlaceholderFragment.newInstance(position + 1))
.commit();
}
public void onSectionAttached(int number) {
switch (number) {
case 1:
mTitle = getString(R.string.title_section1); //The Home Button
break;
case 2:
mTitle = getString(R.string.title_section2);
break;
case 3:
mTitle = getString(R.string.title_section3);
break;
}
}
public void restoreActionBar() {
ActionBar actionBar = getSupportActionBar();
actionBar.setNavigationMode(ActionBar.NAVIGATION_MODE_STANDARD);
actionBar.setDisplayShowTitleEnabled(true);
actionBar.setTitle(mTitle);
}
#Override
public boolean onCreateOptionsMenu(Menu menu) {
if (!mNavigationDrawerFragment.isDrawerOpen()) {
// Only show items in the action bar relevant to this screen
// if the drawer is not showing. Otherwise, let the drawer
// decide what to show in the action bar.
getMenuInflater().inflate(R.menu.main, menu);
restoreActionBar();
return true;
}
return super.onCreateOptionsMenu(menu);
}
#Override
public boolean onOptionsItemSelected(MenuItem item) {
// Handle action bar item clicks here. The action bar will
// automatically handle clicks on the Home/Up button, so long
// as you specify a parent activity in AndroidManifest.xml.
int id = item.getItemId();
//noinspection SimplifiableIfStatement
if (id == R.id.action_settings) {
return true;
}
return super.onOptionsItemSelected(item);
}
/**
* A placeholder fragment containing a simple view.
*/
public static class PlaceholderFragment extends Fragment {
/**
* The fragment argument representing the section number for this
* fragment.
*/
private static final String ARG_SECTION_NUMBER = "section_number";
/**
* Returns a new instance of this fragment for the given section
* number.
*/
public static PlaceholderFragment newInstance(int sectionNumber) {
PlaceholderFragment fragment = new PlaceholderFragment();
Bundle args = new Bundle();
args.putInt(ARG_SECTION_NUMBER, sectionNumber);
fragment.setArguments(args);
return fragment;
}
public PlaceholderFragment() {
}
#Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
View rootView = inflater.inflate(R.layout.fragment_main, container, false);
return rootView;
}
#Override
public void onAttach(Activity activity) {
super.onAttach(activity);
((MainActivity) activity).onSectionAttached(
getArguments().getInt(ARG_SECTION_NUMBER));
}
}
}
And this is HomePage.java :
import java.util.ArrayList;
import java.util.List;
import org.json.JSONArray;
import org.json.JSONException;
import org.json.JSONObject;
import android.app.ListActivity;
import android.app.ProgressDialog;
import android.content.Context;
import android.content.Intent;
import android.os.AsyncTask;
import android.os.Bundle;
import android.text.Html;
import android.util.Log;
import android.view.LayoutInflater;
import android.view.View;
import android.widget.AdapterView;
import android.widget.AdapterView.OnItemClickListener;
import android.widget.Button;
import android.widget.ListView;
import android.widget.TextView;
public class HomePage extends ListActivity {
//Create a progress dialog instance
private ProgressDialog pDialog;
// JSON Node names
private static final String TAG_ARTICLES = "articles";
private static final String TAG_ID = "id";
private static final String TAG_TITLE = "title";
private static final String TAG_TEASER = "teaser";
private static final String TAG_COVER_PHOTO = "cover_photo";
String call_url = "http://www.ana.fm/api/main/?start=0&count=20";
int start_get = 0;
int count_get = 20;
int lastItemIndex = 0;
ListView lv;
//Articles JSONArray
JSONArray articles = null;
//Defining the articles list with type Article
List<Article> articleList;
Button loadMoreButton;
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.home_page);
articleList = new ArrayList<>();
//Getting the ListView
lv = getListView();
//add the footer before adding the adapter, else the footer will not load!
View footerView = ((LayoutInflater) this.getSystemService(Context.LAYOUT_INFLATER_SERVICE)).inflate(R.layout.list_footer, null, false);
lv.addFooterView(footerView);
//Add click listener to the load more button
loadMoreButton = (Button) findViewById(R.id.loadMoreBtn);
loadMoreButton.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
lastItemIndex = lv.getLastVisiblePosition();
start_get = start_get + 20;
call_url = "http://www.ana.fm/api/main/?start=".concat(String.valueOf(start_get)).concat("&count=20");
// Calling async task to get json
new GetArticles().execute();
}
});
// Listview on item click listener
lv.setOnItemClickListener(new OnItemClickListener() {
#Override
public void onItemClick(AdapterView<?> parent, View view,
int position, long id) {
String article_id = ((TextView) view.findViewById(R.id.article_id))
.getText().toString();
// Starting single article activity
Intent in = new Intent(getApplicationContext(),
SingleArticleActivity.class);
in.putExtra(TAG_ID, article_id);
startActivity(in);
}
});
// Calling async task to get json
new GetArticles().execute();
}
/**
* Async task class to get json by making HTTP call
*/
private class GetArticles extends AsyncTask<Void, Void, Void> {
#Override
protected void onPreExecute() {
super.onPreExecute();
// Showing progress dialog
pDialog = new ProgressDialog(HomePage.this);
pDialog.setMessage("Please wait...");
pDialog.setCancelable(false);
pDialog.show();
}
#Override
protected Void doInBackground(Void... arg0) {
// Creating service handler class instance
ServiceHandler sh = new ServiceHandler();
// Making a request to url and getting response
//call_url is defined previously
String jsonStr = sh.makeServiceCall(call_url, ServiceHandler.GET);
if (jsonStr != null) {
try {
JSONObject jsonObj = new JSONObject(jsonStr);
// Getting JSON Array node
articles = jsonObj.getJSONArray(TAG_ARTICLES);
// looping through All Articles
for (int i = 0; i < articles.length(); i++) {
JSONObject c = articles.getJSONObject(i);
String id = c.getString(TAG_ID);
String title = c.getString(TAG_TITLE);
title = Html.fromHtml(title).toString();
String teaser = c.getString(TAG_TEASER);
teaser = Html.fromHtml(teaser).toString();
String cover_photo = "http://www.ana.fm/med_photos/articles/";
cover_photo = cover_photo.concat(c.getString(TAG_COVER_PHOTO));
//Getting an object from the Article class
Article article = new Article();
//Setting the values to the object's variables
article.setId(id);
article.setTitle(title);
article.setTeaser(teaser);
article.setImageUrl(cover_photo);
// adding article to the article list
articleList.add(article);
}
} catch (JSONException e) {
e.printStackTrace();
}
} else {
Log.e("ServiceHandler", "Couldn't get any data from the url");
//new GetContacts().execute();
}
return null;
}
#Override
protected void onPostExecute(Void result) {
super.onPostExecute(result);
// Dismiss the progress dialog
if (pDialog.isShowing())
pDialog.dismiss();
/**
* Calling my custom adapter to view the images as well
* */
MyAdapter adapter = new MyAdapter(getApplicationContext(), R.layout.list_item, articleList);
setListAdapter(adapter);
lv.setSelection(lastItemIndex);
}
}
}
Now what i want is to be navigated to the HomePage.java after clicking on the "Home" button on the Navigation Drawer (Side Menu).
Anyone can help ?

I'm new to android but from what i understand from google's official documentation, they are really similar, refer to the documentation here

Button and menus stop working after orientation change

I have an Android app which uses tabs and fragments for navigation. The app works fine when launched, but after I change the orientation the menu items and the widgets in the fragments stop working. The app works if I put
android:configChanges="orientation|screenSize"
in the manifest, but in the Android documentation it says that this should be a last resort, so I'm wondering if there is a better solution. Here's the code for the host activity and one of the fragments.
package com.mynews;
import android.app.ActionBar;
import android.app.ActionBar.Tab;
import android.app.Activity;
import android.app.Fragment;
import android.app.FragmentTransaction;
import android.os.Bundle;
import android.view.Menu;
public class MainActivity extends Activity {
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
//setContentView(R.layout.activity_main);
//stopService(new Intent(this, FindArticlesService.class));
ActionBar actionBar = getActionBar();
actionBar.setNavigationMode(ActionBar.NAVIGATION_MODE_TABS);
Tab tab = actionBar.newTab()
.setText("Articles")
.setTabListener(new TabListener<Articles>(this, "articles", Articles.class));
actionBar.addTab(tab);
tab = actionBar.newTab()
.setText("Websites")
.setTabListener(new TabListener<UserSites>(this, "websites", UserSites.class));
actionBar.addTab(tab);
tab = actionBar.newTab()
.setText("Add a website")
.setTabListener(new TabListener<AddSites>(this, "add a site", AddSites.class));
actionBar.addTab(tab);
}
#Override
public boolean onCreateOptionsMenu(Menu menu) {
// Inflate the menu; this adds items to the action bar if it is present.
//getMenuInflater().inflate(R.menu.main, menu);
return true;
}
#Override
protected void onSaveInstanceState(Bundle outState) {
// TODO Auto-generated method stub
super.onSaveInstanceState(outState);
}
#Override
protected void onDestroy() {
// TODO Auto-generated method stub
super.onDestroy();
////Intent intent = new Intent(this, FindArticlesService.class);
//this.startService(intent);
}
public static class TabListener<T extends Fragment> implements ActionBar.TabListener {
Fragment fragment;
final Activity activity;
final String tag;
final Class<T> mClass;
public TabListener(Activity a, String s, Class<T> c){
activity = a;
tag = s;
mClass = c;
}
#Override
public void onTabReselected(Tab tab, FragmentTransaction ft) {
// TODO Auto-generated method stub
}
#Override
public void onTabSelected(Tab tab, FragmentTransaction ft) {
// TODO Auto-generated method stub
if(fragment == null){
fragment = Fragment.instantiate(activity, mClass.getName());
ft.add(android.R.id.content, fragment, tag);
}else{
ft.attach(fragment);
}
}
#Override
public void onTabUnselected(Tab tab, FragmentTransaction ft) {
// TODO Auto-generated method stub
if(fragment != null){
ft.detach(fragment);
}
activity.closeContextMenu();
}
}
}
My Fragment Class
package com.mynews;
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.ObjectInputStream;
import java.io.ObjectOutputStream;
import java.net.MalformedURLException;
import java.util.ArrayList;
import android.app.AlertDialog;
import android.app.Dialog;
import android.app.DialogFragment;
import android.app.Fragment;
import android.content.Context;
import android.os.Bundle;
import android.view.LayoutInflater;
import android.view.Menu;
import android.view.MenuInflater;
import android.view.MenuItem;
import android.view.View;
import android.view.View.OnClickListener;
import android.view.ViewGroup;
import android.widget.Button;
import android.widget.EditText;
import android.widget.Toast;
public class AddSites extends Fragment {
public AddSites(){}
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
//setContentView(R.layout.activity_add_sites);
// Show the Up button in the action bar.
setHasOptionsMenu(true);
}
#Override
public void onActivityCreated(Bundle savedInstanceState) {
// TODO Auto-generated method stub
super.onActivityCreated(savedInstanceState);
Button button = (Button) getActivity().findViewById(R.id.add);
button.setOnClickListener(new OnClickListener() {
#Override
public void onClick(View v) {
// TODO Auto-generated method stub
UserSitesFunc usf = new UserSitesFunc(); //create a new UserSitesFunc to hold
try{ //the list of sites
FileInputStream fis = getActivity().openFileInput("MySites.ser");//check if there's a file
ObjectInputStream ois = new ObjectInputStream(fis);//with a USF object
usf = (UserSitesFunc) ois.readObject(); //if there is, deserialize it and use it
ois.close();//instead of a brand new object
}catch(IOException e){ //catch various exceptions
e.printStackTrace();
}catch(Exception ep){
ep.printStackTrace();
}finally{
try{ //do this with either the new object or the deserialised one
EditText website = (EditText) getActivity().findViewById(R.id.editText1);//get the input
EditText keywords = (EditText) getActivity().findViewById(R.id.editText2);//from the user
String web = website.getText().toString(); //store it in strings
String key = keywords.getText().toString();
String[] kwords = key.split(", ");
ArrayList<String> newKeywords = new ArrayList<String>();
for(String s:kwords){
newKeywords.add(s);
}
Sites s = new Sites(web, newKeywords);//create a new site from the input
if(usf.siteList.contains(s)){
showContainedDialog();
return;
}
usf.addSite(s);//add it to the user's list of sites
FileOutputStream fs = getActivity().openFileOutput("MySites.ser", Context.MODE_PRIVATE);//save it
ObjectOutputStream oos = new ObjectOutputStream(fs);
oos.writeObject(usf);
oos.close();
Toast.makeText(getActivity(), web + " added to Tracked Websites", Toast.LENGTH_LONG).show();
website.setText("");
keywords.setText("");
}catch(MalformedURLException mue){
showDialog();
}catch(Exception ex){
ex.printStackTrace();
}
}
}
});
}
#Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
// TODO Auto-generated method stub
View view = inflater.inflate(R.layout.activity_add_sites, container, false);
return view;
}
#Override
public void onCreateOptionsMenu(Menu menu, MenuInflater inflater) {
menu.clear();
inflater.inflate(R.menu.add_sites, menu);
super.onCreateOptionsMenu(menu, inflater);
}
#Override
public boolean onOptionsItemSelected(MenuItem item) {
switch (item.getItemId()) {
case android.R.id.home:
// This ID represents the Home or Up button. In the case of this
// activity, the Up button is shown. Use NavUtils to allow users
// to navigate up one level in the application structure. For
// more details, see the Navigation pattern on Android Design:
//
// http://developer.android.com/design/patterns/navigation.html#up-vs-back
//
return true;
}
return super.onOptionsItemSelected(item);
}
public static class NotAWebsiteDialog extends DialogFragment {
public static NotAWebsiteDialog newInstance(){
NotAWebsiteDialog notAWebsite = new NotAWebsiteDialog();
Bundle args = new Bundle();
notAWebsite.setArguments(args);
return notAWebsite;
}
#Override
public Dialog onCreateDialog(final Bundle savedInstanceState) {
// TODO Auto-generated method stub
return new AlertDialog.Builder(getActivity())
.setMessage("Please enter a vaild web address")
.create();
}
}
public void showDialog(){
DialogFragment dialog = NotAWebsiteDialog.newInstance();
dialog.show(getFragmentManager(), "Not A Website");
}
public static class AlreadyContainsWebsiteDialog extends DialogFragment {
public static AlreadyContainsWebsiteDialog newInstance(){
AlreadyContainsWebsiteDialog containsAWebsite = new AlreadyContainsWebsiteDialog();
Bundle args = new Bundle();
containsAWebsite.setArguments(args);
return containsAWebsite;
}
#Override
public Dialog onCreateDialog(final Bundle savedInstanceState) {
// TODO Auto-generated method stub
return new AlertDialog.Builder(getActivity())
.setMessage("This website is already being tracked")
.create();
}
}
public void showContainedDialog(){
DialogFragment dialog = AlreadyContainsWebsiteDialog.newInstance();
dialog.show(getFragmentManager(), "Contains this Website");
}
}

Kudos for not taking the easy way... keep up your programming efforts!
Refer to my answer here regarding the use of Menus and their host Fragments.

Getting checkout button to navigate to checkout page

I am working in Eclipse and struggling with a certain step in my assignment so any help would be appriciated because I actually dont know how to do it even though I realise how glaringly simple it probably is...
I have a shopping app and I have created my CheckoutActivity... now... it needs to start when the user clicks the checkout button in my CartActivity.
I need to add code in the ocCreate method of my CartActivity (which I will provide below) that specifies the listener for the Checkout button. then I need to define a button variable named btn inside the onCreate. I then need to assign the button element from the view using the id that you specified in my activity_cart.xml layout.
All I have so far is this... and I have no idea what to do...
btn.setOnClickListener(new OnClickListener() {
public void onClick(final View v) {
//I cant figure out how to get it to start the CheckoutActivity
}
});
Just in case you need to see the code I have so far... here is the code I have for my cartActivty
package uk.ac.uk.st265.shopper;
import java.text.DecimalFormat;
import java.util.List;
import java.util.ResourceBundle.Control;
import android.os.Bundle;
import android.app.Activity;
import android.content.Context;
import android.content.Intent;
import android.view.LayoutInflater;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.view.ViewGroup;
import android.widget.BaseAdapter;
import android.widget.Button;
import android.widget.ImageView;
import android.widget.ListView;
import android.widget.TextView;
import android.support.v4.app.NavUtils;
public class CartActivity extends Activity {
CartListAdapter adapter;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_cart);
TextView text = (TextView) findViewById(R.id.total_price); // its not in
// XML
DecimalFormat df = new DecimalFormat("#.00");
text.setText("£"
+ df.format(((ShopperApp) getApplication()).getCartTotal()));
adapter = new CartListAdapter(this);
ListView cartList = (ListView) findViewById(R.id.cart_list);
adapter.setItemList(((ShopperApp) getApplication()).cart);
cartList.setAdapter(adapter);
// Show the Up button in the action bar.
setupActionBar();
//work5ass2part6
//btn.setOnClickListener(new OnClickListener() {
//public void onClick(final View v) {
// I cant figure out how to get it to start the CheckoutActivity
//}
//});
}
/**
* Set up the {#link android.app.ActionBar}.
*/
private void setupActionBar() {
getActionBar().setDisplayHomeAsUpEnabled(true);
}
#Override
public boolean onCreateOptionsMenu(Menu menu) {
// Inflate the menu; this adds items to the action bar if it is present.
getMenuInflater().inflate(R.menu.cart, menu);
return true;
}
public class CartListAdapter extends BaseAdapter {
private final Context context;
private List<Product> itemList;
public CartListAdapter(Context c) {
context = c;
}
public void setItemList(List<Product> itemList) {
// this.itemList = itemList;
}
#Override
public int getCount() {
// TODO Auto-generated method stub
return 0;
}
#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) {
View cell = convertView;
if (cell == null) {
// get layout from mobile xml
LayoutInflater inflater = ((Activity) context)
.getLayoutInflater();
cell = inflater.inflate(R.layout.adapter_cart, parent, false);
}
Product p = itemList.get(position);
// set value into text view according to position
TextView textView = (TextView) cell
.findViewById(R.id.product_title);
textView.setText(p.getProductName());
textView = (TextView) cell.findViewById(R.id.product_info);
textView.setText("Price " + p.getPrice());
// set value into image view according to position
ImageView imgView = (ImageView) cell
.findViewById(R.id.product_image);
// clear the image
imgView.setImageDrawable(null);
// and load from the network
p.loadImage(imgView, 54, 54);
return cell;
}
public List<Product> getItemList() {
return itemList;
}
}
#Override
public boolean onOptionsItemSelected(MenuItem item) {
switch (item.getItemId()) {
case android.R.id.home:
// This ID represents the Home or Up button. In the case of this
// activity, the Up button is shown. Use NavUtils to allow users
// to navigate up one level in the application structure. For
// more details, see the Navigation pattern on Android Design:
//
// http://developer.android.com/design/patterns/navigation.html#up-vs-back
//
case R.id.show_cart:
// Create the intent for the cart activity
Intent intent = new Intent(getApplicationContext(),
CartActivity.class);
startActivity(intent);
NavUtils.navigateUpFromSameTask(this);
return true;
}
return super.onOptionsItemSelected(item);
}
}
and here is the code I have so far on my CheckoutActivity:
package uk.ac.uk.st265.shopper;
import android.os.Bundle;
import android.app.Activity;
import android.view.Menu;
import android.view.MenuItem;
import android.support.v4.app.NavUtils;
public class CheckoutActivity extends Activity {
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_checkout);
// Show the Up button in the action bar.
setupActionBar();
}
/**
* Set up the {#link android.app.ActionBar}.
*/
private void setupActionBar() {
getActionBar().setDisplayHomeAsUpEnabled(true);
}
#Override
public boolean onCreateOptionsMenu(Menu menu) {
// Inflate the menu; this adds items to the action bar if it is present.
getMenuInflater().inflate(R.menu.checkout, menu);
return true;
}
#Override
public boolean onOptionsItemSelected(MenuItem item) {
switch (item.getItemId()) {
case android.R.id.home:
// This ID represents the Home or Up button. In the case of this
// activity, the Up button is shown. Use NavUtils to allow users
// to navigate up one level in the application structure. For
// more details, see the Navigation pattern on Android Design:
//
// http://developer.android.com/design/patterns/navigation.html#up-vs-back
//
NavUtils.navigateUpFromSameTask(this);
return true;
}
return super.onOptionsItemSelected(item);
}
}

Intent myIntent = new Intent(CurrentActivity.this, NextActivity.class);
// myIntent.putExtra("key", value); //if you want to pass parameter
CurrentActivity.this.startActivity(myIntent);