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Unable to start activity: NullPointerException [duplicate]

This question already has answers here:
What is a NullPointerException, and how do I fix it?
(12 answers)
Closed 8 years ago.
Hi I am encountering a null pointer error when I click on the activity Links. The purpose of my feature is to call a list of links in the form of list view. Below is the logcat and as far as I understand it is coming from my onItemClickListener, but I can't seem to point out the null error.:
sitesList.setOnItemClickListener(new OnItemClickListener()
Links.java
package com.example.sgrecipe;
import java.io.FileNotFoundException;
import android.app.Activity;
import android.content.Context;
import android.content.Intent;
import android.net.ConnectivityManager;
import android.net.NetworkInfo;
import android.net.Uri;
import android.os.AsyncTask;
import android.os.Bundle;
import android.util.Log;
import android.view.View;
import android.widget.AdapterView;
import android.widget.AdapterView.OnItemClickListener;
import android.widget.ListView;
public class Links extends Activity {
private SitesAdapter mAdapter;
private ListView sitesList;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
Log.i("StackSites", "OnCreate()");
setContentView(R.layout.activity_main);
//Get reference to our ListView
sitesList = (ListView)findViewById(R.id.sitesList);
//Set the click listener to launch the browser when a row is clicked.
sitesList.setOnItemClickListener(new OnItemClickListener() {
#Override
public void onItemClick(AdapterView<?> parent, View v, int pos,long id) {
String url = mAdapter.getItem(pos).getLink();
Intent i = new Intent(Intent.ACTION_VIEW);
i.setData(Uri.parse(url));
startActivity(i);
}
});
/*
* If network is available download the xml from the Internet.
* If not then try to use the local file from last time.
*/
if(isNetworkAvailable()){
Log.i("StackSites", "starting download Task");
SitesDownloadTask download = new SitesDownloadTask();
download.execute();
}else{
mAdapter = new SitesAdapter(getApplicationContext(), -1, SitesXmlPullParser.getStackSitesFromFile(Links.this));
sitesList.setAdapter(mAdapter);
}
}
//Helper method to determine if Internet connection is available.
private boolean isNetworkAvailable() {
ConnectivityManager connectivityManager
= (ConnectivityManager) getSystemService(Context.CONNECTIVITY_SERVICE);
NetworkInfo activeNetworkInfo = connectivityManager.getActiveNetworkInfo();
return activeNetworkInfo != null && activeNetworkInfo.isConnected();
}
/*
* AsyncTask that will download the xml file for us and store it locally.
* After the download is done we'll parse the local file.
*/
private class SitesDownloadTask extends AsyncTask<Void, Void, Void>{
#Override
protected Void doInBackground(Void... arg0) {
//Download the file
try {
Downloader.DownloadFromUrl("https://dl.dropboxusercontent.com/u/5724095/XmlParseExample/stacksites.xml", openFileOutput("StackSites.xml", Context.MODE_PRIVATE));
} catch (FileNotFoundException e) {
e.printStackTrace();
}
return null;
}
#Override
protected void onPostExecute(Void result){
//setup our Adapter and set it to the ListView.
mAdapter = new SitesAdapter(Links.this, -1, SitesXmlPullParser.getStackSitesFromFile(Links.this));
sitesList.setAdapter(mAdapter);
Log.i("StackSites", "adapter size = "+ mAdapter.getCount());
}
}
}
activity_links.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"
tools:context=".Links" >
<ListView
android:id="#+id/sitesList"
android:layout_width="match_parent"
android:layout_height="match_parent" />
</RelativeLayout>
row_site.xml (for the listview)
<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:padding="10dp" >
<ProgressBar
android:id="#+id/progress"
android:layout_width="wrap_content"
android:layout_height="wrap_content" />
<ImageView
android:id="#+id/iconImg"
android:layout_width="80dp"
android:layout_height="80dp"
android:layout_marginRight="8dp" />
<TextView
android:id="#+id/nameTxt"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_toRightOf="#id/iconImg"
android:textSize="16sp"
android:textStyle="bold" />
<TextView
android:id="#+id/aboutTxt"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_toRightOf="#id/iconImg"
android:textSize="12sp"
android:layout_below="#id/nameTxt"
/>
</RelativeLayout>
Here is the logcat:
02-23 15:13:10.856: E/AndroidRuntime(8201): FATAL EXCEPTION: main
02-23 15:13:10.856: E/AndroidRuntime(8201): Process: com.example.sgrecipe, PID: 8201
02-23 15:13:10.856: E/AndroidRuntime(8201): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.sgrecipe/com.example.sgrecipe.Links}: java.lang.NullPointerException
02-23 15:13:10.856: E/AndroidRuntime(8201): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2292)
02-23 15:13:10.856: E/AndroidRuntime(8201): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2350)
02-23 15:13:10.856: E/AndroidRuntime(8201): at android.app.ActivityThread.access$800(ActivityThread.java:163)
02-23 15:13:10.856: E/AndroidRuntime(8201): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1257)
02-23 15:13:10.856: E/AndroidRuntime(8201): at android.os.Handler.dispatchMessage(Handler.java:102)
02-23 15:13:10.856: E/AndroidRuntime(8201): at android.os.Looper.loop(Looper.java:157)
02-23 15:13:10.856: E/AndroidRuntime(8201): at android.app.ActivityThread.main(ActivityThread.java:5335)
02-23 15:13:10.856: E/AndroidRuntime(8201): at java.lang.reflect.Method.invokeNative(Native Method)
02-23 15:13:10.856: E/AndroidRuntime(8201): at java.lang.reflect.Method.invoke(Method.java:515)
02-23 15:13:10.856: E/AndroidRuntime(8201): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1265)
02-23 15:13:10.856: E/AndroidRuntime(8201): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1081)
02-23 15:13:10.856: E/AndroidRuntime(8201): at dalvik.system.NativeStart.main(Native Method)
02-23 15:13:10.856: E/AndroidRuntime(8201): Caused by: java.lang.NullPointerException
02-23 15:13:10.856: E/AndroidRuntime(8201): at com.example.sgrecipe.Links.onCreate(Links.java:36)
02-23 15:13:10.856: E/AndroidRuntime(8201): at android.app.Activity.performCreate(Activity.java:5389)
02-23 15:13:10.856: E/AndroidRuntime(8201): at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1105)
02-23 15:13:10.856: E/AndroidRuntime(8201): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2256)
Any help is really appreciate, thank you!

Change following line
setContentView(R.layout.activity_main);
to
setContentView(R.layout.activity_links);

Seems like your using different layouts:
setContentView(R.layout.activity_main);
vs
activity_links.xml

App Crashing (Unable to start ComponentInfo Error) [duplicate]

This question already has answers here:
NullPointerException accessing views in onCreate()
(13 answers)
Closed 8 years ago.
I am having trouble finding the source of the crash in my application. I've done a clean/build. I'm very new to Android dev so I'm still learning. From looking at the logcat, I think there maybe some null error exception that might have something to do with the calculate function. Any help or guidance is appreciated.
The java code:
package com.example.rectangle;
import java.text.DecimalFormat;
import android.support.v7.app.ActionBarActivity;
import android.support.v7.app.ActionBar;
import android.support.v4.app.Fragment;
import android.content.Context;
import android.os.Bundle;
import android.view.KeyEvent;
import android.view.LayoutInflater;
import android.view.Menu;
import android.view.MenuItem;
import android.view.MotionEvent;
import android.view.View;
import android.view.ViewGroup;
import android.view.inputmethod.InputMethodManager;
import android.widget.Button;
import android.widget.EditText;
import android.widget.TextView;
import android.widget.TextView.OnEditorActionListener;
import android.os.Build;
public class MainActivity extends ActionBarActivity implements OnEditorActionListener {
//graphical variables
private EditText widthInput;
private EditText heightInput;
private TextView areaOutput;
private TextView perimeterOutput;
private Button calculateButton;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
//assign ids to graphical variables
widthInput = (EditText) findViewById(R.id.widthEditText);
heightInput = (EditText) findViewById(R.id.heightEditText);
areaOutput = (TextView) findViewById(R.id.areaOutput);
perimeterOutput = (TextView) findViewById(R.id.perimterOutput);
calculateButton = (Button) findViewById(R.id.calculateButton);
widthInput.setOnEditorActionListener(this);
heightInput.setOnEditorActionListener(this);
//calculate and display
calculateAreaAndPerimeter();
}
//hide keyboard
//source: http://stackoverflow.com/questions/8697499/hide-keyboard-when-user-taps-anywhere-else-on-the-screen-in-android
#Override
public boolean onTouchEvent(MotionEvent event) {
InputMethodManager imm = (InputMethodManager)getSystemService(Context.
INPUT_METHOD_SERVICE);
imm.hideSoftInputFromWindow(getCurrentFocus().getWindowToken(), 0);
return 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.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.
int id = item.getItemId();
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 {
public PlaceholderFragment() {
}
#Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
View rootView = inflater.inflate(R.layout.fragment_main, container, false);
return rootView;
}
}
//display
public void display(String area, String perimeter)
{
areaOutput.setText(area);
perimeterOutput.setText(perimeter);
}
//algorithms
private void calculateAreaAndPerimeter()
{
//get width and height
String widthInputString = widthInput.getText().toString();
String heightInputString = heightInput.getText().toString();
float width = Float.parseFloat(widthInputString);
float height = Float.parseFloat(heightInputString);
//calculate and display
DecimalFormat df = new DecimalFormat();
df.setMaximumFractionDigits(2);
float area;
area = width * height;
String areaString = (df.format(area)) + "";
float perimeter;
perimeter = (width * 2) + (height * 2);
String perimeterString = (df.format(perimeter)) + "";
display(areaString, perimeterString);
}
#Override
public boolean onEditorAction(TextView v, int actionId, KeyEvent event) {
// TODO Auto-generated method stub
calculateAreaAndPerimeter();
return false;
}
}
The logcat:
11-12 13:05:14.049: E/AndroidRuntime(10535): FATAL EXCEPTION: main
11-12 13:05:14.049: E/AndroidRuntime(10535): Process: com.example.rectangle, PID: 10535
11-12 13:05:14.049: E/AndroidRuntime(10535): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.rectangle/com.example.rectangle.MainActivity}: java.lang.NullPointerException
11-12 13:05:14.049: E/AndroidRuntime(10535): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2198)
11-12 13:05:14.049: E/AndroidRuntime(10535): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2257)
11-12 13:05:14.049: E/AndroidRuntime(10535): at android.app.ActivityThread.access$800(ActivityThread.java:139)
11-12 13:05:14.049: E/AndroidRuntime(10535): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1210)
11-12 13:05:14.049: E/AndroidRuntime(10535): at android.os.Handler.dispatchMessage(Handler.java:102)
11-12 13:05:14.049: E/AndroidRuntime(10535): at android.os.Looper.loop(Looper.java:136)
11-12 13:05:14.049: E/AndroidRuntime(10535): at android.app.ActivityThread.main(ActivityThread.java:5086)
11-12 13:05:14.049: E/AndroidRuntime(10535): at java.lang.reflect.Method.invokeNative(Native Method)
11-12 13:05:14.049: E/AndroidRuntime(10535): at java.lang.reflect.Method.invoke(Method.java:515)
11-12 13:05:14.049: E/AndroidRuntime(10535): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:785)
11-12 13:05:14.049: E/AndroidRuntime(10535): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:601)
11-12 13:05:14.049: E/AndroidRuntime(10535): at dalvik.system.NativeStart.main(Native Method)
11-12 13:05:14.049: E/AndroidRuntime(10535): Caused by: java.lang.NullPointerException
11-12 13:05:14.049: E/AndroidRuntime(10535): at com.example.rectangle.MainActivity.onCreate(MainActivity.java:46)
11-12 13:05:14.049: E/AndroidRuntime(10535): at android.app.Activity.performCreate(Activity.java:5248)
11-12 13:05:14.049: E/AndroidRuntime(10535): at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1110)
11-12 13:05:14.049: E/AndroidRuntime(10535): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2162)
11-12 13:05:14.049: E/AndroidRuntime(10535): ... 11 more
Fragment_main
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:paddingBottom="#dimen/activity_vertical_margin"
android:paddingLeft="#dimen/activity_horizontal_margin"
android:paddingRight="#dimen/activity_horizontal_margin"
android:paddingTop="#dimen/activity_vertical_margin"
tools:context=".MainActivity$PlaceholderFragment" >
<TextView
android:id="#+id/heightTextView"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_alignLeft="#+id/widthTextView"
android:layout_below="#+id/widthTextView"
android:layout_marginTop="29dp"
android:text="Height"
android:textAppearance="?android:attr/textAppearanceMedium" />
<TextView
android:id="#+id/areaTextView"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_alignLeft="#+id/heightTextView"
android:layout_below="#+id/heightTextView"
android:layout_marginTop="30dp"
android:text="Area"
android:textAppearance="?android:attr/textAppearanceMedium" />
<TextView
android:id="#+id/perimeterTextView"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_alignLeft="#+id/areaTextView"
android:layout_below="#+id/areaTextView"
android:layout_marginTop="40dp"
android:text="Perimeter"
android:textAppearance="?android:attr/textAppearanceMedium" />
<EditText
android:id="#+id/heightEditText"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_alignBottom="#+id/heightTextView"
android:layout_alignLeft="#+id/widthEditText"
android:layout_alignRight="#+id/widthEditText"
android:ems="10"
android:inputType="numberSigned"
android:text="0.0" />
<TextView
android:id="#+id/widthTextView"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_alignParentLeft="true"
android:layout_alignParentTop="true"
android:layout_marginTop="35dp"
android:text="Width"
android:textAppearance="?android:attr/textAppearanceMedium" />
<EditText
android:id="#+id/widthEditText"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_above="#+id/heightTextView"
android:layout_alignParentRight="true"
android:ems="10"
android:inputType="numberDecimal"
android:text="0.0" />
<TextView
android:id="#+id/areaOutput"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_alignBottom="#+id/areaTextView"
android:layout_marginLeft="38dp"
android:layout_toRightOf="#+id/perimeterTextView"
android:text="0.0"
android:textAppearance="?android:attr/textAppearanceMedium" />
<TextView
android:id="#+id/perimterOutput"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_alignBaseline="#+id/perimeterTextView"
android:layout_alignBottom="#+id/perimeterTextView"
android:layout_alignLeft="#+id/areaOutput"
android:text="0.0"
android:textAppearance="?android:attr/textAppearanceMedium" />
</RelativeLayout>

Try this:
TextView.OnEditorActionListener listener = new TextView.OnEditorActionListener() {
#Override
public boolean onEditorAction(TextView v, int actionId, KeyEvent event) {
// TODO Auto-generated method stub
calculateAreaAndPerimeter();
return false;
}
};
The compile may still want to the one you have, and if, so create one like the above.
I think you have to tell the compiler its a listener, even though it may have created the method you have. Android Studio doesn't create listener syntax very well and I typically have to go back and surround a new public method with the listener stuff. Hope that works!

Application successfully installed but stops working when run in emulator

I am trying to create a simple application that can sign in / sign up users . All the data are
stored in Mysql database .
My app was installed successfully but as I opened it, it gave an error saying "Unfortunately, 'myapp' has stop working".
I have read almost all related problems posted here but no luck!
here's from logcat .
07-25 01:22:31.452: E/AndroidRuntime(2101): FATAL EXCEPTION: main
07-25 01:22:31.452: E/AndroidRuntime(2101): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.mysqltest/com.example.mobileapp.MainActivity}: android.view.InflateException: Binary XML file line #2: Error inflating class android.widget.RelativeLayout
07-25 01:22:31.452: E/AndroidRuntime(2101): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2211)
07-25 01:22:31.452: E/AndroidRuntime(2101): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2261)
07-25 01:22:31.452: E/AndroidRuntime(2101): at android.app.ActivityThread.access$600(ActivityThread.java:141)
07-25 01:22:31.452: E/AndroidRuntime(2101): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1256)
07-25 01:22:31.452: E/AndroidRuntime(2101): at android.os.Handler.dispatchMessage(Handler.java:99)
07-25 01:22:31.452: E/AndroidRuntime(2101): at android.os.Looper.loop(Looper.java:137)
07-25 01:22:31.452: E/AndroidRuntime(2101): at android.app.ActivityThread.main(ActivityThread.java:5103)
07-25 01:22:31.452: E/AndroidRuntime(2101): at java.lang.reflect.Method.invokeNative(Native Method)
07-25 01:22:31.452: E/AndroidRuntime(2101): at java.lang.reflect.Method.invoke(Method.java:525)
07-25 01:22:31.452: E/AndroidRuntime(2101): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:737)
07-25 01:22:31.452: E/AndroidRuntime(2101): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:553)
07-25 01:22:31.452: E/AndroidRuntime(2101): at dalvik.system.NativeStart.main(Native Method)
07-25 01:22:31.452: E/AndroidRuntime(2101): Caused by: android.view.InflateException: Binary XML file line #2: Error inflating class android.widget.RelativeLayout
07-25 01:22:31.452: E/AndroidRuntime(2101): at android.view.LayoutInflater.createView(LayoutInflater.java:620)
07-25 01:22:31.452: E/AndroidRuntime(2101): at com.android.internal.policy.impl.PhoneLayoutInflater.onCreateView(PhoneLayoutInflater.java:56)
07-25 01:22:31.452: E/AndroidRuntime(2101): at android.view.LayoutInflater.onCreateView(LayoutInflater.java:669)
07-25 01:22:31.452: E/AndroidRuntime(2101): at android.view.LayoutInflater.createViewFromTag(LayoutInflater.java:694)
07-25 01:22:31.452: E/AndroidRuntime(2101): at android.view.LayoutInflater.inflate(LayoutInflater.java:469)
07-25 01:22:31.452: E/AndroidRuntime(2101): at android.view.LayoutInflater.inflate(LayoutInflater.java:397)
07-25 01:22:31.452: E/AndroidRuntime(2101): at android.view.LayoutInflater.inflate(LayoutInflater.java:353)
07-25 01:22:31.452: E/AndroidRuntime(2101): at com.android.internal.policy.impl.PhoneWindow.setContentView(PhoneWindow.java:267)
07-25 01:22:31.452: E/AndroidRuntime(2101): at android.app.Activity.setContentView(Activity.java:1895)
07-25 01:22:31.452: E/AndroidRuntime(2101): at com.example.mobileapp.MainActivity.onCreate(MainActivity.java:45)
07-25 01:22:31.452: E/AndroidRuntime(2101): at android.app.Activity.performCreate(Activity.java:5133)
07-25 01:22:31.452: E/AndroidRuntime(2101): at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1087)
07-25 01:22:31.452: E/AndroidRuntime(2101): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2175)
07-25 01:22:31.452: E/AndroidRuntime(2101): ... 11 more
07-25 01:22:31.452: E/AndroidRuntime(2101): Caused by: java.lang.reflect.InvocationTargetException
07-25 01:22:31.452: E/AndroidRuntime(2101): at java.lang.reflect.Constructor.constructNative(Native Method)
07-25 01:22:31.452: E/AndroidRuntime(2101): at java.lang.reflect.Constructor.newInstance(Constructor.java:417)
07-25 01:22:31.452: E/AndroidRuntime(2101): at android.view.LayoutInflater.createView(LayoutInflater.java:594)
07-25 01:22:31.452: E/AndroidRuntime(2101): ... 23 more
07-25 01:22:31.452: E/AndroidRuntime(2101): Caused by: java.lang.OutOfMemoryError
07-25 01:22:31.452: E/AndroidRuntime(2101): at android.graphics.BitmapFactory.nativeDecodeAsset(Native Method)
07-25 01:22:31.452: E/AndroidRuntime(2101): at android.graphics.BitmapFactory.decodeStream(BitmapFactory.java:503)
07-25 01:22:31.452: E/AndroidRuntime(2101): at android.graphics.BitmapFactory.decodeResourceStream(BitmapFactory.java:356)
07-25 01:22:31.452: E/AndroidRuntime(2101): at android.graphics.drawable.Drawable.createFromResourceStream(Drawable.java:800)
07-25 01:22:31.452: E/AndroidRuntime(2101): at android.content.res.Resources.loadDrawable(Resources.java:2105)
07-25 01:22:31.452: E/AndroidRuntime(2101): at android.content.res.TypedArray.getDrawable(TypedArray.java:601)
07-25 01:22:31.452: E/AndroidRuntime(2101): at android.view.View.<init>(View.java:3364)
07-25 01:22:31.452: E/AndroidRuntime(2101): at android.view.View.<init>(View.java:3293)
07-25 01:22:31.452: E/AndroidRuntime(2101): at android.view.ViewGroup.<init>(ViewGroup.java:453)
07-25 01:22:31.452: E/AndroidRuntime(2101): at android.widget.RelativeLayout.<init>(RelativeLayout.java:242)
activity_main.xml
<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:background="#drawable/background" >
<TextView
android:id="#+id/tv2"
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:layout_above="#+id/password"
android:layout_alignParentLeft="true"
android:layout_marginBottom="14dp"
android:text="Password" />
<TextView
android:id="#+id/tv"
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:layout_alignParentBottom="true"
android:layout_alignParentLeft="true"
android:layout_marginBottom="20dp" />
<TextView
android:id="#+id/tv0"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_above="#+id/tv1"
android:layout_alignParentLeft="true"
android:layout_alignParentRight="true"
android:layout_marginBottom="38dp"
android:gravity="center"
android:text="PhilTaxWindow User Login"
android:textSize="20sp"
android:textStyle="bold" />
<TextView
android:id="#+id/tv1"
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:layout_above="#+id/username"
android:layout_alignParentLeft="true"
android:layout_marginBottom="18dp"
android:text="Username" />
<TextView
android:id="#+id/textView1"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_alignBaseline="#+id/register"
android:layout_alignBottom="#+id/register"
android:layout_marginRight="17dp"
android:layout_toLeftOf="#+id/register"
android:text="Don't Have an Account?"
android:textAppearance="?android:attr/textAppearanceSmall" />
<Button
android:id="#+id/Button01"
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:layout_above="#+id/register"
android:layout_alignParentLeft="true"
android:layout_marginBottom="60dp"
android:text="Login" />
<EditText
android:id="#+id/username"
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:layout_above="#+id/tv2"
android:layout_alignParentLeft="true"
android:layout_marginBottom="22dp"
android:ems="10"
android:inputType="textPersonName"
android:singleLine="true" >
<requestFocus />
</EditText>
<EditText
android:id="#+id/password"
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:layout_above="#+id/Button01"
android:layout_alignParentLeft="true"
android:layout_marginBottom="31dp"
android:ems="10"
android:inputType="textPassword"
android:singleLine="true" />
<Button
android:id="#+id/register"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_above="#+id/tv"
android:layout_alignParentRight="true"
android:layout_marginBottom="17dp"
android:layout_marginRight="29dp"
android:text="Register here" />
</RelativeLayout>
mainactivity.java
package com.example.mobileapp;
import java.util.ArrayList;
import java.util.List;
import org.apache.http.NameValuePair;
import org.apache.http.message.BasicNameValuePair;
import org.json.JSONException;
import org.json.JSONObject;
import com.example.mysqltest.R;
import android.app.Activity;
import android.app.ProgressDialog;
import android.content.Intent;
import android.os.AsyncTask;
import android.os.Bundle;
import android.util.Log;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;
import android.widget.EditText;
import android.widget.Toast;
public class MainActivity extends Activity implements OnClickListener{
private EditText Username, Password;
private Button Submit, Register;
private ProgressDialog Dialog;
JSONParser jsonParser = new JSONParser();
private static final String LOGIN_URL = "http://192.168.1.4/checkingPHP/CheckUser.php";
private static final String TAG_SUCCESS = "success";
private static final String TAG_MESSAGE = "message";
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
Username = (EditText)findViewById(R.id.username);
Password = (EditText)findViewById(R.id.password);
Submit = (Button)findViewById(R.id.Button01);
Register = (Button)findViewById(R.id.register);
Submit.setOnClickListener(this);
Register.setOnClickListener(this);
}
#Override
public void onClick(View v) {
switch (v.getId()) {
case R.id.Button01:
new AttemptLogin().execute();
break;
case R.id.register:
Intent i = new Intent(this, Register.class);
startActivity(i);
break;
default:
break;
}
}
class AttemptLogin extends AsyncTask<String, String, String> {
boolean failure = false;
#Override
protected void onPreExecute() {
super.onPreExecute();
Dialog = new ProgressDialog(MainActivity.this);
Dialog.setMessage("Validating...");
Dialog.setIndeterminate(false);
Dialog.setCancelable(true);
Dialog.show();
}
#Override
protected String doInBackground(String... args) {
int success;
String username = Username.getText().toString();
String password = Password.getText().toString();
try {
List<NameValuePair> params = new ArrayList<NameValuePair>();
params.add(new BasicNameValuePair("Username", username));
params.add(new BasicNameValuePair("Password", password));
Log.d("request!", "starting");
JSONObject json = jsonParser.makeHttpRequest(
LOGIN_URL, "POST", params);
Log.d("Login attempt", json.toString());
success = json.getInt(TAG_SUCCESS);
if (success == 1) {
Log.d("Login Successful!", json.toString());
Intent i = new Intent(MainActivity.this, WelcomPage.class);
finish();
startActivity(i);
return json.getString(TAG_MESSAGE);
}else{
Log.d("Login Failure!", json.getString(TAG_MESSAGE));
return json.getString(TAG_MESSAGE);
}
} catch (JSONException e) {
e.printStackTrace();
}
return null;
}
#Override
protected void onPostExecute(String file_url) {
Dialog.dismiss();
if (file_url != null){
Toast.makeText(MainActivity.this, file_url, Toast.LENGTH_LONG).show();
}
}
}
}

The emulator ran into out of memory exception
Caused by: java.lang.OutOfMemoryError due to
android:background="#drawable/background"
The image that you are trying to load is causing this. Try reducing the image resolution.

Android App Counter Button [duplicate]

This question already has answers here:
NullPointerException accessing views in onCreate()
(13 answers)
Closed 8 years ago.
When I try to open this page it crashes. I have tried to make this button count various ways and can't get it to count! I have tried all kinds of tutorials by thenewboston and other people but it doesn't work for me.
Medical.java
package com.fullcyclestudios.rust;
import android.support.v7.app.ActionBarActivity;
import android.support.v4.app.Fragment;
import android.os.Bundle;
import android.app.Activity;
import android.view.LayoutInflater;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.view.ViewGroup;
import android.widget.Button;
import android.widget.TextView;
import android.content.Intent;
public class Medical extends ActionBarActivity {
Button add, sub;
int counter;
TextView textView;
TextView quantityDisplay;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_medical);
add=(Button) findViewById(R.id.addButtonMedical);
sub=(Button) findViewById(R.id.minusButtonMedical);
quantityDisplay = (TextView) findViewById(R.id.textViewQuantityMedical);
counter=1;
add.setOnClickListener(new View.OnClickListener()
{
#Override
public void onClick(View arg0)
{
// TODO Auto-generated method stub
counter++;
quantityDisplay.setText("it"+counter);
}
});
sub.setOnClickListener(new View.OnClickListener()
{
#Override
public void onClick(View v)
{
// TODO Auto-generated method stub
counter--;
quantityDisplay.setText("it"+counter);
}
});
Intent intent = getIntent();
if (savedInstanceState == null) {
getSupportFragmentManager().beginTransaction()
.add(R.id.container, new PlaceholderFragment()).commit();
}
}
#Override
public boolean onCreateOptionsMenu(Menu menu) {
// Inflate the menu; this adds items to the action bar if it is present.
getMenuInflater().inflate(R.menu.medical, 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.
int id = item.getItemId();
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 {
public PlaceholderFragment() {
}
#Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
View rootView = inflater.inflate(R.layout.fragment_medical,
container, false);
return rootView;
}
}
/** Bandage button */
public String bandageMaterials(View view)
{
String materials = "Bandage\r\n\r\n2 Cloth";
textView = (TextView) findViewById(R.id.textViewMatMedical);
textView.setText(materials);
return materials;
}
/** Small Medkit button */
public String smallMedkitMaterials(View view)
{
String materials = "Small Medkit\r\n\r\n2 Cloth\r\n2 Blood";
textView = (TextView) findViewById(R.id.textViewMatMedical);
textView.setText(materials);
return materials;
}
/** Large Medkit button */
public String largeMedkitMaterials(View view)
{
String materials = "Large Medkit\r\n\r\n3 Cloth\r\n3 Blood";
textView = (TextView) findViewById(R.id.textViewMatMedical);
textView.setText(materials);
return materials;
}
}
fragment_medical.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"
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.fullcyclestudios.rust.Medical$PlaceholderFragment" >
<ScrollView
android:id="#+id/scrollViewMedical"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_marginLeft="130dp" >
<LinearLayout
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:orientation="vertical" >
<Button
android:id="#+id/bandageButton"
style="?android:attr/buttonStyleSmall"
android:layout_width="150dp"
android:layout_height="35dp"
android:text="#string/bandage"
android:onClick="bandageMaterials" />
<Button
android:id="#+id/smallMedkitButton"
style="?android:attr/buttonStyleSmall"
android:layout_width="150dp"
android:layout_height="35dp"
android:text="#string/smallMedkit"
android:onClick="smallMedkitMaterials" />
<Button
android:id="#+id/largeMedkitButton"
style="?android:attr/buttonStyleSmall"
android:layout_width="150dp"
android:layout_height="35dp"
android:text="#string/largeMedkit"
android:onClick="largeMedkitMaterials" />
</LinearLayout>
</ScrollView>
<TextView
android:id="#+id/textViewMatMedical"
android:layout_width="120dp"
android:layout_height="fill_parent"
android:layout_marginTop="140dp"
android:background="#color/gray"
android:text="#string/blank" />
<TextView
android:id="#+id/textViewQuantityMedical"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_alignLeft="#+id/minusButtonMedical"
android:layout_alignRight="#+id/minusButtonMedical"
android:layout_below="#+id/addButtonMedical"
android:gravity="center_horizontal"
android:text="#string/one"
android:textAppearance="?android:attr/textAppearanceSmall"
android:textSize="25sp" />
<Button
android:id="#+id/minusButtonMedical"
style="?android:attr/buttonStyleSmall"
android:layout_width="wrap_content"
android:layout_height="50dp"
android:layout_marginTop="80dp"
android:layout_alignLeft="#+id/addButtonMedical"
android:layout_alignRight="#+id/addButtonMedical"
android:text="#string/minus"
android:textSize="30sp"
android:textStyle="bold" />
<Button
android:id="#+id/addButtonMedical"
style="?android:attr/buttonStyleSmall"
android:layout_width="wrap_content"
android:layout_height="50dp"
android:layout_alignLeft="#+id/textViewMatMedical"
android:layout_alignRight="#+id/textViewMatMedical"
android:text="#string/add"
android:textSize="30sp" />
</RelativeLayout>
ERRORS
06-08 16:10:38.890: W/dalvikvm(855): threadid=1: thread exiting with uncaught exception (group=0xb2a40ba8)
06-08 16:10:38.990: E/AndroidRuntime(855): FATAL EXCEPTION: main
06-08 16:10:38.990: E/AndroidRuntime(855): Process: com.fullcyclestudios.rust, PID: 855
06-08 16:10:38.990: E/AndroidRuntime(855): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.fullcyclestudios.rust/com.fullcyclestudios.rust.Medical}: java.lang.NullPointerException
06-08 16:10:38.990: E/AndroidRuntime(855): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2195)
06-08 16:10:38.990: E/AndroidRuntime(855): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2245)
06-08 16:10:38.990: E/AndroidRuntime(855): at android.app.ActivityThread.access$800(ActivityThread.java:135)
06-08 16:10:38.990: E/AndroidRuntime(855): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1196)
06-08 16:10:38.990: E/AndroidRuntime(855): at android.os.Handler.dispatchMessage(Handler.java:102)
06-08 16:10:38.990: E/AndroidRuntime(855): at android.os.Looper.loop(Looper.java:136)
06-08 16:10:38.990: E/AndroidRuntime(855): at android.app.ActivityThread.main(ActivityThread.java:5017)
06-08 16:10:38.990: E/AndroidRuntime(855): at java.lang.reflect.Method.invokeNative(Native Method)
06-08 16:10:38.990: E/AndroidRuntime(855): at java.lang.reflect.Method.invoke(Method.java:515)
06-08 16:10:38.990: E/AndroidRuntime(855): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:779)
06-08 16:10:38.990: E/AndroidRuntime(855): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:595)
06-08 16:10:38.990: E/AndroidRuntime(855): at dalvik.system.NativeStart.main(Native Method)
06-08 16:10:38.990: E/AndroidRuntime(855): Caused by: java.lang.NullPointerException
06-08 16:10:38.990: E/AndroidRuntime(855): at com.fullcyclestudios.rust.Medical.onCreate(Medical.java:33)
06-08 16:10:38.990: E/AndroidRuntime(855): at android.app.Activity.performCreate(Activity.java:5231)
06-08 16:10:38.990: E/AndroidRuntime(855): at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1087)
06-08 16:10:38.990: E/AndroidRuntime(855): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2159)
06-08 16:10:38.990: E/AndroidRuntime(855): ... 11 more
06-08 16:10:43.330: I/Process(855): Sending signal. PID: 855 SIG: 9

Your issue is here:
setContentView(R.layout.activity_medical);
add=(Button) findViewById(R.id.addButtonMedical);
sub=(Button) findViewById(R.id.minusButtonMedical);
but from what you post: addButtonMedical and minusButtonMedical are inside fragment_medical and not activity_medical xml layout!

How do I make the back button I created in the activity change the text in the textView to the previous text created by the random generator?

When I start the activity on my phone, it says that the app is not responding. The problem is the back button which I can't seem to program to make it gather the previous text from the textView.
Xml code for activity
<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"
android:background="#drawable/background"
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=".Author" >
<TextView
android:id="#+id/textView1"
android:layout_width="300dp"
android:layout_height="300dp"
android:layout_alignParentTop="true"
android:layout_centerHorizontal="true"
android:background="#drawable/button_shape"
android:text="#string/Getstarted"
android:textColor="#FFFFFF"
android:textSize="23sp" />
<ImageButton
android:id="#+id/next"
android:layout_width="90dp"
android:layout_height="50dp"
android:layout_alignRight="#+id/textView1"
android:layout_below="#+id/textView1"
android:layout_marginTop="14dp"
android:background="#drawable/button_shape"
android:contentDescription="#string/Next"
android:onClick="NextQuote"
android:src="#drawable/navigationnextitem" />
<ImageButton
android:id="#+id/share"
android:layout_width="90dp"
android:layout_height="50dp"
android:layout_alignTop="#+id/next"
android:layout_centerHorizontal="true"
android:background="#drawable/button_shape"
android:contentDescription="#string/share"
android:onClick="Sharing"
android:src="#drawable/socialshare" />
<ImageButton
android:id="#+id/back"
android:layout_width="90dp"
android:layout_height="50dp"
android:layout_alignLeft="#+id/textView1"
android:layout_alignTop="#+id/next"
android:background="#drawable/button_shape"
android:contentDescription="#string/Back"
android:onClick="PreviousQuote"
android:src="#drawable/navigationpreviousitem" />
</RelativeLayout>
Java code for activity
package com.android.motivateme3;
import java.util.Random;
import android.os.Bundle;
import android.app.Activity;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.widget.Button;
import android.widget.ImageButton;
import android.widget.TextView;
import android.support.v4.app.NavUtils;
import android.annotation.TargetApi;
import android.content.Intent;
import android.os.Build;
public class Author extends Activity {
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_author);
// Show the Up button in the action bar.
setupActionBar();
}
/**
* Set up the {#link android.app.ActionBar}, if the API is available.
*/
#TargetApi(Build.VERSION_CODES.HONEYCOMB)
private void setupActionBar() {
if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.HONEYCOMB) {
getActionBar().setDisplayHomeAsUpEnabled(true);
Button NextQuote = (Button)findViewById(R.id.next);
final TextView display = (TextView) findViewById(R.id.textView1);
NextQuote.setOnClickListener(new View.OnClickListener() {
public void onClick(View v) {
// TODO Auto-generated method stub
Random numGen = new Random();
int rNumber = numGen.nextInt(10);
if (rNumber == 0)
{
display.setText(R.string.Author1);
}
else if (rNumber == 1)
{
display.setText(R.string.Author2);
}
else if (rNumber == 2)
{
display.setText(R.string.Author3);
}
else if (rNumber == 3)
{
display.setText(R.string.Author4);
}
else if (rNumber == 4)
{
display.setText(R.string.Author5);
}
else if (rNumber == 5)
{
display.setText(R.string.Author6);
}
else if (rNumber == 6)
{
display.setText(R.string.Author7);
}
else if (rNumber == 7)
{
display.setText(R.string.Author8);
}
else if (rNumber == 8)
{
display.setText(R.string.Author9);
}
else if (rNumber == 9)
{
display.setText(R.string.Author10);
} }
});
}
ImageButton Sharing = (ImageButton)findViewById(R.id.share);
Sharing.setOnClickListener(new View.OnClickListener() {
public void onClick(View v){
TextView text = (TextView)findViewById(R.id.textView1);
String quote = text.getText().toString();{
Intent shareIntent = new Intent(android.content.Intent.ACTION_SEND);
shareIntent.setType("plain/text");
shareIntent.putExtra(android.content.Intent.EXTRA_SUBJECT, "This is a great quote (from the Motivate Me! app)");
shareIntent.putExtra(android.content.Intent.EXTRA_TEXT, quote);
startActivity(Intent.createChooser(shareIntent, "Share via:"));}}});
Button BackQuote = (Button)findViewById(R.id.back);
final TextView display = (TextView) findViewById(R.id.textView1);
BackQuote.setOnClickListener(new View.OnClickListener() {
public void onClick(View v) {
String prev = (String) display.getText();
display.setText(prev);
}
});}
#Override
public boolean onCreateOptionsMenu(Menu menu) {
// Inflate the menu; this adds items to the action bar if it is present.
getMenuInflater().inflate(R.menu.author, 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);
}
}
This is the stack trace
04-03 14:29:34.174: E/AndroidRuntime(17383): at android.app.ActivityThread.main(ActivityThread.java:4441)
04-03 14:29:34.174: E/AndroidRuntime(17383): at java.lang.reflect.Method.invokeNative(Native Method)
04-03 14:29:34.174: E/AndroidRuntime(17383): at java.lang.reflect.Method.invoke(Method.java:511)
04-03 14:29:34.174: E/AndroidRuntime(17383): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:823)
04-03 14:29:34.174: E/AndroidRuntime(17383): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:590)
04-03 14:29:34.174: E/AndroidRuntime(17383): at dalvik.system.NativeStart.main(Native Method)
04-03 14:29:34.174: E/AndroidRuntime(17383): Caused by: java.lang.ClassCastException: android.widget.ImageButton cannot be cast to android.widget.Button
04-03 14:29:34.174: E/AndroidRuntime(17383): at com.android.motivateme3.Author.setupActionBar(Author.java:36)
04-03 14:29:34.174: E/AndroidRuntime(17383): at com.android.motivateme3.Author.onCreate(Author.java:25)
04-03 14:29:34.174: E/AndroidRuntime(17383): at android.app.Activity.performCreate(Activity.java:4465)
04-03 14:29:34.174: E/AndroidRuntime(17383): at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1049)
04-03 14:29:34.174: E/AndroidRuntime(17383): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1931)
04-03 14:29:34.174: E/AndroidRuntime(17383): ... 11 more
04-03 14:29:41.664: I/Process(17383): Sending signal. PID: 17383 SIG: 9

It seems to me that R.id.next refers to an ImageButton, which cannot be cast into a Button, since it is not a subclass of a Button
Do you happen to see a ClassCastException?
To fix that particular issue, replace:
Button NextQuote = (Button)findViewById(R.id.next);
with
ImageButton NextQuote = (ImageButton)findViewById(R.id.next);