setOnCheckedListener will crash my app

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I am trying to set a toggle-button. I created a button in the xml-file, but always when I activate setOnCheckedChangeListener(this); my app crashs.

If I comment it out, there is no problem to run my app.

    ToggleButton t;
    LinearLayout l;

public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.tt1);

        //Start und Stop Button
        t=(ToggleButton) findViewById(R.id.toggleButton1);
        t.setOnCheckedChangeListener(this);
        l=(LinearLayout)findViewById(R.id.layout);



@Override
    public void onCheckedChanged(CompoundButton buttonView, boolean isChecked) {
        if (isChecked) {
            //onPause();
            l.setBackgroundColor(Color.BLUE);
                    } 
        else {
                //onResume();
            l.setBackgroundColor(Color.GRAY);
        }


    }

03-24 22:49:03.980: E/AndroidRuntime(1504): FATAL EXCEPTION: main
03-24 22:49:03.980: E/AndroidRuntime(1504): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.bikinifigur2/de.basti12354.tage.uebungen.Tag1}: java.lang.NullPointerException
03-24 22:49:03.980: E/AndroidRuntime(1504):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2211)
03-24 22:49:03.980: E/AndroidRuntime(1504):     at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2261)
03-24 22:49:03.980: E/AndroidRuntime(1504):     at android.app.ActivityThread.access$600(ActivityThread.java:141)
03-24 22:49:03.980: E/AndroidRuntime(1504):     at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1256)
03-24 22:49:03.980: E/AndroidRuntime(1504):     at android.os.Handler.dispatchMessage(Handler.java:99)
03-24 22:49:03.980: E/AndroidRuntime(1504):     at android.os.Looper.loop(Looper.java:137)
03-24 22:49:03.980: E/AndroidRuntime(1504):     at android.app.ActivityThread.main(ActivityThread.java:5103)
03-24 22:49:03.980: E/AndroidRuntime(1504):     at java.lang.reflect.Method.invokeNative(Native Method)
03-24 22:49:03.980: E/AndroidRuntime(1504):     at java.lang.reflect.Method.invoke(Method.java:525)
03-24 22:49:03.980: E/AndroidRuntime(1504):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:737)
03-24 22:49:03.980: E/AndroidRuntime(1504):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:553)
03-24 22:49:03.980: E/AndroidRuntime(1504):     at dalvik.system.NativeStart.main(Native Method)
03-24 22:49:03.980: E/AndroidRuntime(1504): Caused by: java.lang.NullPointerException
03-24 22:49:03.980: E/AndroidRuntime(1504):     at de.basti12354.tage.uebungen.Tag1.onCreate(Tag1.java:51)
03-24 22:49:03.980: E/AndroidRuntime(1504):     at android.app.Activity.performCreate(Activity.java:5133)
03-24 22:49:03.980: E/AndroidRuntime(1504):     at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1087)
03-24 22:49:03.980: E/AndroidRuntime(1504):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2175)
03-24 22:49:03.980: E/AndroidRuntime(1504):     ... 11 more

asked 41 secs ago

user3433232

16