Unfortunately (android app) has stopped.

Question

I am learning android programming using eclipse. I coded a twitter app that simply let's you tweet a status and view a user's timeline. However when I try run the app on my samsung galaxy tab 3.0 the app starts up, all i see is the title at the top, none of the textviews or buttons show up then after 2 seconds the screen goes black and i get the error message ("Unfortunately TwitterApp has stopped") I cant imagine it's something to do with twitter since none of the widgets are being displayed. Here is the code from my main activity, and the activity_main.xml file. And the logCat. Ill even include the manifest

package com.example.twitterapp;

import java.util.List;

import twitter4j.Twitter;
import twitter4j.TwitterException;
import twitter4j.TwitterFactory;
import android.os.AsyncTask;
import android.os.Bundle;
import android.app.Activity;
import android.text.Editable;
import android.text.TextWatcher;
import android.text.method.ScrollingMovementMethod;
import android.view.Menu;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;
import android.widget.EditText;
import android.widget.TextView;

public class MainActivity extends Activity {

TextView countCharsTV, timelineTV;
EditText usernameET, tweetET;
Button tweetBTN, timelineBTN;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);

    countCharsTV = (TextView) findViewById(R.id.textView1);

    timelineTV = (TextView) findViewById(R.id.textView2);
    timelineTV.setMovementMethod(new ScrollingMovementMethod());

    tweetET = (EditText) findViewById(R.id.editText1);
    tweetET.addTextChangedListener(new MyTextWatcher());

    usernameET = (EditText) findViewById(R.id.editText2);

    tweetBTN = (Button) findViewById(R.id.button1);
    tweetBTN.setOnClickListener(tweetBTNOnClickListener);

    timelineBTN.setOnClickListener(timelineBTNOnClickListener);
}

//BUTTON CLICK LISTENERS WITHOUT IMPLEMENTS
public OnClickListener tweetBTNOnClickListener = new OnClickListener() {

    @Override
    public void onClick(View arg0) {

        new MyAsyncTaskTweet().execute(tweetET.getText().toString());

    }
};

public OnClickListener timelineBTNOnClickListener = new OnClickListener() {

    @Override
    public void onClick(View v) {
        new MyAsyncTaskTimeline().execute(timelineTV.getText().toString());

    }
};
//END OF BUTTON CLICK LISTENERS

//COUNT CHARS IN TEXTVIEW USING IMPLEMENTS
class MyTextWatcher implements TextWatcher {

    @Override
    public void afterTextChanged(Editable arg0) {

        countCharsTV.setText("" + tweetET.getText().length());

    }

    @Override
    public void beforeTextChanged(CharSequence arg0, int arg1, int arg2,
            int arg3) {

    }

    @Override
    public void onTextChanged(CharSequence arg0, int arg1, int arg2,
            int arg3) {

    }


}
//End OF COUNT CHARS IN TEXTVIEW

//ASYNC TASK CLASSES
//TWEET ASYNC TASK
public class MyAsyncTaskTweet extends AsyncTask<String,Void,String> {

    @Override
    protected String doInBackground(String... tweet) {

        String result = "";

        Twitter twitter = TwitterFactory.getSingleton();

        try{

            twitter.updateStatus(tweet[0]);
            result = "Success";

        }catch(TwitterException twitterException) {

            result = "Failed to update status";

        }

        return result;

    }

    @Override
    protected void onPostExecute(String result){

        tweetET.setHint(result);
        tweetET.setText("");

    }

    }
//END OF TWEET ASYNC TASK

public class MyAsyncTaskTimeline extends AsyncTask<String, Void, String> {

    @Override
    protected String doInBackground(String... username) {

        String result = new String("");
        List<twitter4j.Status> statuses = null;

        Twitter twitter = TwitterFactory.getSingleton();
        try {

            statuses = twitter.getUserTimeline(username[0]);


        }catch (TwitterException twitterException) {

            twitterException.printStackTrace();

        }


        for(twitter4j.Status status : statuses) {

            result += status.getText();
            result += "\n";

        }
        return result;
    }

    @Override
    protected void onPostExecute(String result) {

        usernameET.setText("");
        timelineTV.setText(result);

    }


}

@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;
}

}

activity_main.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=".MainActivity" >

<Button
    android:id="@+id/button1"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_alignLeft="@+id/editText1"
    android:layout_below="@+id/editText1"
    android:text="Tweet" />

<EditText
    android:id="@+id/editText1"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_alignLeft="@+id/textView1"
    android:layout_alignParentTop="true"
    android:ems="10"
    android:hint="Type your tweet here" />

<TextView
    android:id="@+id/textView1"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_alignBaseline="@+id/editText2"
    android:layout_alignBottom="@+id/editText2"
    android:layout_toLeftOf="@+id/editText2"
    android:text="&apos;@" />

<Button
    android:id="@+id/button2"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_below="@+id/editText2"
    android:layout_toRightOf="@+id/textView1"
    android:text="Timeline" />

<EditText
    android:id="@+id/editText2"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_below="@+id/button1"
    android:layout_centerHorizontal="true"
    android:layout_marginTop="19dp"
    android:ems="10"
    android:hint="Type a username here" >

    <requestFocus />
</EditText>

<TextView
    android:id="@+id/textView2"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_below="@+id/button2"
    android:layout_toRightOf="@+id/button1"
    android:text="Timeline will go here" />

</RelativeLayout>

AndroidManifest.xml

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
package="com.example.twitterapp"
android:versionCode="1"
android:versionName="1.0" >

<uses-sdk
    android:minSdkVersion="8"
    android:targetSdkVersion="17" />
uses-permission android:name="android.permission.INTERNET"/>

<application
    android:allowBackup="true"
    android:icon="@drawable/ic_launcher"
    android:label="@string/app_name"
    android:theme="@style/AppTheme" >
    <activity
        android:name="com.example.twitterapp.MainActivity"
        android:label="@string/app_name" >
        android:windowSoftInputMode="adjustPan">
        <intent-filter>
            <action android:name="android.intent.action.MAIN" />

            <category android:name="android.intent.category.LAUNCHER" />
        </intent-filter>
    </activity>
</application>

</manifest>

Logcat

03-21 22:46:25.117: W/ActivityThread(3806): Application com.example.twitterapp can be        

debugged on port 8100...
03-21 22:46:25.289: E/SensorManager(3806): thread start
03-21 22:46:25.296: D/SensorManager(3806): registerListener :: handle = 1598182229      
name= BOSCH BMC150 Acceleration Sensor delay= 200000    
03-21 22:46:25.296: D/AndroidRuntime(3806): Shutting down VM
03-21 22:46:25.296: W/dalvikvm(3806): threadid=1: thread exiting with uncaught exception        
(group=0x40dcd2a0)
03-21 22:46:25.304: E/AndroidRuntime(3806): FATAL EXCEPTION: main
03-21 22:46:25.304: E/AndroidRuntime(3806): java.lang.RuntimeException: Unable to start     
activity ComponentInfo{com.example.twitterapp/com.example.twitterapp.MainActivity}:    
java.lang.NullPointerException
03-21 22:46:25.304: E/AndroidRuntime(3806):     at    
android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2129)
03-21 22:46:25.304: E/AndroidRuntime(3806):     at   
android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2154)
03-21 22:46:25.304: E/AndroidRuntime(3806):     at  
android.app.ActivityThread.access$700(ActivityThread.java:146)
03-21 22:46:25.304: E/AndroidRuntime(3806):     at   
android.app.ActivityThread$H.handleMessage(ActivityThread.java:1260)
03-21 22:46:25.304: E/AndroidRuntime(3806):     at 
android.os.Handler.dispatchMessage(Handler.java:99)
03-21 22:46:25.304: E/AndroidRuntime(3806):     at  
android.os.Looper.loop(Looper.java:137)
03-21 22:46:25.304: E/AndroidRuntime(3806):     at 
android.app.ActivityThread.main(ActivityThread.java:4949)
03-21 22:46:25.304: E/AndroidRuntime(3806):     at   
java.lang.reflect.Method.invokeNative(Native Method)
03-21 22:46:25.304: E/AndroidRuntime(3806):     at  
java.lang.reflect.Method.invoke(Method.java:511)
03-21 22:46:25.304: E/AndroidRuntime(3806):     at  
com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1043)
03-21 22:46:25.304: E/AndroidRuntime(3806):     at 
com.android.internal.os.ZygoteInit.main(ZygoteInit.java:810)
03-21 22:46:25.304: E/AndroidRuntime(3806):     at  
dalvik.system.NativeStart.main(Native Method)
03-21 22:46:25.304: E/AndroidRuntime(3806): Caused by: java.lang.NullPointerException
03-21 22:46:25.304: E/AndroidRuntime(3806):     at 
com.example.twitterapp.MainActivity.onCreate(MainActivity.java:45)
03-21 22:46:25.304: E/AndroidRuntime(3806):     at 
android.app.Activity.performCreate(Activity.java:5185)
03-21 22:46:25.304: E/AndroidRuntime(3806):     at 
android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1094)
03-21 22:46:25.304: E/AndroidRuntime(3806):     at          
android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2093)
03-21 22:46:25.304: E/AndroidRuntime(3806):     ... 11 more
03-21 22:46:38.398: I/Process(3806): Sending signal. PID: 3806 SIG: 9

Answer 1

Where is timelineBTN reference? "timelineBTN" was null. timelineBTN = (Button)findViewById(R.id.);