我正在尝试创建我的第一个Android应用程序（游戏），但我在开始时遇到了一些困难。
当我运行我的代码时，我收到此错误日志：
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
我认为问题是这个“线程退出未捕获的异常”部分，我不知道异常是什么或导致它的原因。
这是我的代码：
NMGView.java： 包com.stickfigs.NMG;
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 e.g. 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's 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's 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's 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");
}
}
}
更新：这是我的R.java和nmg_layout.xml：
R.java： 包com.stickfigs.nmg;
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>
答案 0 :(得分：16)
如果查看堆栈跟踪，您将看到“由......引起”行（有时不止一行）。最后一个是重要的一个。它说NMG.java的第32行有一个空指针异常。该行以及之前的行是：
nMGView = (NMGView) findViewById(R.id.nmg);
nMGThread = nMGView.getThread();
显然，状态R.id.nmg中没有ID为R.layout.nmg_layout的视图。这就是造成你问题的原因。
答案 1 :(得分：1)
在您的XML文件中，R.id.nmg确实存在。
所以我认为问题是由资源中的NMGView对象膨胀引起的。
您应该检查NMGView源代码，尤其是在其构造函数中。
答案 2 :(得分：1)
如果您在“ build.gradle（Module：app）”中使用“ multiDexEnabled true ”，请从“ defaultConfig ”中删除此行>”并同步项目。
就我而言，它可以工作！！！！
答案 3 :(得分：0)
出现这个问题是因为大多数时候SurfaceView onDraw（）方法在你破坏surfaceView时运行，然后你得到一个NULL POINTER ERROR，因为那一刻画布不存在。我已经修复了使用NullPointerException捕获所有绘图内容的问题：
@Override
public void onDraw(Canvas canvas) {
try {
//Drawing Stuff
}catch(NullPointerException e){
Log.e("NULL POINTER EXCEPTION","Canvas NULL POINTER");
}
}
如果在Main活动中实现onPause（），onDestroy（）方法，您将获得以下顺序：first：E / onPause：ON PAUSE - ＆gt; next E / surfaceDestroyed：SURFACE DESTROYED - ＆gt; E / NULL指针异常：Canvas NULL POINTER - ＆gt;最后 E / onDestroy：DESTROY
这是我正在使用的surfaceDestroyed方法：
@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");
}
}