Android development: "thread exiting with an uncaught exception"

Question

I am trying to create my first Android application (game), but I had difficulty launching it.

When I run my code, I get this error log:

05-25 02:41:51.022: WARN/dalvikvm(634): threadid=1: thread exiting with uncaught exception (group=0x4001d800) 05-25 02:41:51.040: ERROR/AndroidRuntime(634): FATAL EXCEPTION: main 05-25 02:41:51.040: ERROR/AndroidRuntime(634): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.stickfigs.nmg/com.stickfigs.nmg.NMG}: java.lang.NullPointerException 05-25 02:41:51.040: ERROR/AndroidRuntime(634): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2663) 05-25 02:41:51.040: ERROR/AndroidRuntime(634): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2679) 05-25 02:41:51.040: ERROR/AndroidRuntime(634): at android.app.ActivityThread.access$2300(ActivityThread.java:125) 05-25 02:41:51.040: ERROR/AndroidRuntime(634): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:2033) 05-25 02:41:51.040: ERROR/AndroidRuntime(634): at android.os.Handler.dispatchMessage(Handler.java:99) 05-25 02:41:51.040: ERROR/AndroidRuntime(634): at android.os.Looper.loop(Looper.java:123) 05-25 02:41:51.040: ERROR/AndroidRuntime(634): at android.app.ActivityThread.main(ActivityThread.java:4627) 05-25 02:41:51.040: ERROR/AndroidRuntime(634): at java.lang.reflect.Method.invokeNative(Native Method) 05-25 02:41:51.040: ERROR/AndroidRuntime(634): at java.lang.reflect.Method.invoke(Method.java:521) 05-25 02:41:51.040: ERROR/AndroidRuntime(634): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:868) 05-25 02:41:51.040: ERROR/AndroidRuntime(634): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:626) 05-25 02:41:51.040: ERROR/AndroidRuntime(634): at dalvik.system.NativeStart.main(Native Method) 05-25 02:41:51.040: ERROR/AndroidRuntime(634): Caused by: java.lang.NullPointerException 05-25 02:41:51.040: ERROR/AndroidRuntime(634): at com.stickfigs.nmg.NMG.onCreate(NMG.java:32) 05-25 02:41:51.040: ERROR/AndroidRuntime(634): at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1047) 05-25 02:41:51.040: ERROR/AndroidRuntime(634): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2627) 05-25 02:41:51.040: ERROR/AndroidRuntime(634): ... 11 more 05-25 02:41:51.062: WARN/ActivityManager(59): Force finishing activity com.stickfigs.nmg/.NMG 

I think the problem is that this part is "thread exiting with an uncaught exception", I have no idea what could be the exception or what causes it.

Here is my code:

NMGView.java: com.stickfigs.NMG package;

 import android.content.Context; import android.os.Bundle; import android.util.AttributeSet; import android.view.SurfaceHolder; import android.view.SurfaceView; class NMGView extends SurfaceView implements SurfaceHolder.Callback { class NMGThread extends Thread { //State-tracking constants public static final int STATE_LOSE = 1; public static final int STATE_PAUSE = 2; public static final int STATE_READY = 3; public static final int STATE_RUNNING = 4; public static final int STATE_WIN = 5; /** The state of the game. One of READY, RUNNING, PAUSE, LOSE, or WIN */ private int mode; /** Handle to the surface manager object we interact with */ private SurfaceHolder surfaceHolder; public NMGThread(SurfaceHolder surfaceHolderc, Context contextc) { // get handles to some important objects surfaceHolder = surfaceHolderc; context = contextc; } /** * Restores game state from the indicated Bundle. Typically called when * the Activity is being restored after having been previously * destroyed. * * @param savedState Bundle containing the game state */ public synchronized void restoreState(Bundle savedState) { synchronized (surfaceHolder) { setState(STATE_PAUSE); } } /** * Sets the game mode. That is, whether we are running, paused, in the * failure state, in the victory state, etc. * * @param mode one of the STATE_* constants * @param message string to add to screen or null */ public void setState(int modec) { synchronized (surfaceHolder) { mode = modec; } } } @Override public void surfaceChanged(SurfaceHolder holder, int format, int width, int height) { // TODO Auto-generated method stub } @Override public void surfaceCreated(SurfaceHolder holder) { // TODO Auto-generated method stub } @Override public void surfaceDestroyed(SurfaceHolder holder) { // TODO Auto-generated method stub } /** Handle to the application context, used to eg fetch Drawables. */ private Context context; /** The thread that actually draws the animation */ private NMGThread thread; public NMGView(Context context, AttributeSet attrs) { super(context, attrs); // register our interest in hearing about changes to our surface SurfaceHolder holder = getHolder(); holder.addCallback(this); // create thread only; it started in surfaceCreated() thread = new NMGThread(holder, context); setFocusable(true); // make sure we get key events } /** * Fetches the animation thread corresponding to this LunarView. * * @return the animation thread */ public NMGThread getThread() { return thread; } } 

NMG.java:

 package com.stickfigs.nmg; import android.app.Activity; import android.os.Bundle; import android.util.Log; import android.view.Window; import com.stickfigs.nmg.NMGView.NMGThread; public class NMG extends Activity { /** Called when the activity is first created. */ /** A handle to the thread that actually running the animation. */ private NMGThread nMGThread; /** A handle to the View in which the game is running. */ private NMGView nMGView; @Override public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); //Turn off the window title bar // TODO Turn off the status bar requestWindowFeature(Window.FEATURE_NO_TITLE); // tell system to use the layout defined in our XML file setContentView(R.layout.nmg_layout); // get handles to the LunarView from XML, and its LunarThread nMGView = (NMGView) findViewById(R.id.nmg); nMGThread = nMGView.getThread(); if (savedInstanceState == null) { // we were just launched: set up a new game nMGThread.setState(NMGThread.STATE_READY); Log.w(this.getClass().getName(), "SIS is null"); } else { // we are being restored: resume a previous game nMGThread.restoreState(savedInstanceState); Log.w(this.getClass().getName(), "SIS is nonnull"); } } } 

UPDATE: Here are my R.java and nmg_layout.xml:

R.java: com.stickfigs.nmg package;

 public final class R { public static final class attr { } public static final class drawable { public static final int icon=0x7f020000; } public static final class id { public static final int nmg=0x7f050000; } public static final class layout { public static final int nmg_layout=0x7f030000; } public static final class string { public static final int app_name=0x7f040001; public static final int hello=0x7f040000; } } 

nmg_layout.xml:

 <?xml version="1.0" encoding="utf-8"?> <FrameLayout xmlns:android="http://schemas.android.com/apk/res/android" android:layout_width="fill_parent" android:layout_height="fill_parent"> <com.stickfigs.nmg.NMGView android:id="@+id/nmg" android:layout_width="fill_parent" android:layout_height="fill_parent"/> </FrameLayout> 

Answer 1

If you look at the stack trace, you will see the line "Caused by ..." (sometimes more than one). The last one is important. It says that line 32 of NMG.java had a null pointer exception. This line and the line before it:

 nMGView = (NMGView) findViewById(R.id.nmg); nMGThread = nMGView.getThread(); 

Obviously there is no view with id R.id.nmg in the layout of R.layout.nmg_layout . This is what causes your problem.

Answer 2

In your XML file R.id.nmg exist. Therefore, I think the problem is caused by inflating the NMGView object from the resource. You should study the source code of NMGView , especially in its constructor.

Answer 3

These problems arise because most of the time the SurfaceView onDraw () method is launched when you destroy the surfaceView, then you get a NULL POINTER ERROR, because by that time the canvas does not exist. I fixed this problem by catching all drawing elements with a NullPointerException:

 @Override public void onDraw(Canvas canvas) { try { //Drawing Stuff }catch(NullPointerException e){ Log.e("NULL POINTER EXCEPTION","Canvas NULL POINTER"); } } 

If you implement the methods onPause (), onDestroy () in your main activity, you will get the following order: first: E / onPause: ON PAUSE → next E / surfaceDestroyed: SURFACE REMOVED → E / NULL POINTER EXCLUSION: Canvas NULL POINTER → finally E / onDestroy: ON DESTROY

This is the surfaceDestroyed method that I use:

  @Override public void surfaceDestroyed(SurfaceHolder arg0) { Log.e("surfaceDestroyed", "SURFACE DESTROYED "); thread.setRunning(false); try { //thread.setRunning(false); thread.join(); } catch (InterruptedException e) { Log.e("Surface Thread Stopped","SURFACE THREAD STOPPED"); } }