Question

I am working on a program and i am using an intent in a button to switch between activities.

It keeps crashing my app (it gives me the unable to resume activity,java.lang.nullPointer Exception error) and i cant seem to figure out why my code is below.

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

    final Button button1 = (Button) findViewById(R.id.button1);
    button1.setOnClickListener(new View.OnClickListener() {
        public void onClick(View v) {
            // Perform action on click
            Intent i= new Intent(Main.this,LocationMonitor.class);
            startActivity(i);
        }
    });

    final Button button2 = (Button) findViewById(R.id.button2);
    button2.setOnClickListener(new View.OnClickListener() {
        public void onClick(View v) {
            // Perform action on click
            finish();
        }
    });
}

Below is the activity being launched:

public class LocationMonitor extends Activity implements LocationListener {
    private static final String TAG = "LocationDemo";
    private static final String[] S = { "Out of Service",
        "Temporarily Unavailable", "Available" };

    private TextView output;
    private LocationManager locationManager;
    private String bestProvider;
    private double myLat;
    private double myLong;


    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.locationlayout);


            output.append("\n\n" + location.toString());
    }

}

Error Log Post:

  03-11 22:28:42.785: E/AndroidRuntime(6817): Uncaught handler: thread main exiting due to uncaught exception
  03-11 22:28:42.796: E/AndroidRuntime(6817): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.android.POG_version1/com.android.POG_version1.LocationMonitor}: java.lang.NullPointerException
  03-11 22:28:42.796: E/AndroidRuntime(6817):   at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2496)
  03-11 22:28:42.796: E/AndroidRuntime(6817):   at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2512)
  03-11 22:28:42.796: E/AndroidRuntime(6817):   at android.app.ActivityThread.access$2200(ActivityThread.java:119)
  03-11 22:28:42.796: E/AndroidRuntime(6817):   at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1863)
  03-11 22:28:42.796: E/AndroidRuntime(6817):   at android.os.Handler.dispatchMessage(Handler.java:99)
  03-11 22:28:42.796: E/AndroidRuntime(6817):   at android.os.Looper.loop(Looper.java:123)
  03-11 22:28:42.796: E/AndroidRuntime(6817):   at android.app.ActivityThread.main(ActivityThread.java:4363)
  03-11 22:28:42.796: E/AndroidRuntime(6817):   at java.lang.reflect.Method.invokeNative(Native Method)
  03-11 22:28:42.796: E/AndroidRuntime(6817):   at java.lang.reflect.Method.invoke(Method.java:521)
  03-11 22:28:42.796: E/AndroidRuntime(6817):   at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:860)
  03-11 22:28:42.796: E/AndroidRuntime(6817):   at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:618)
  03-11 22:28:42.796: E/AndroidRuntime(6817):   at dalvik.system.NativeStart.main(Native Method)
  03-11 22:28:42.796: E/AndroidRuntime(6817): Caused by: java.lang.NullPointerException
  03-11 22:28:42.796: E/AndroidRuntime(6817):   at com.android.POG_version1.LocationMonitor.onCreate(LocationMonitor.java:60)
  03-11 22:28:42.796: E/AndroidRuntime(6817):   at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1047)
  03-11 22:28:42.796: E/AndroidRuntime(6817):   at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2459)

Answer 1

Make sure you are correctly initializing locationManager when you first start your Activity. Your implementation is throwing a NullPointerException when you try to make the call locationManager.requestLocationUpdates().