我创建了一个Android应用程序,它可以在屏幕上绘制一个小图像并退出,如果你点击屏幕的底部50px。当我点击它时,它退出正常,但是,当我按下后面(或主页)按钮退出应用程序时,它退出,但随后说,“不幸的是,游戏开发已停止。”我还检查了LogCat,它显示每次停止工作时都会发生Java NullPointerException。 LogCat的输出是:
10-30 01:13:28.280: E/AndroidRuntime(15294): FATAL EXCEPTION: Thread-1718
10-30 01:13:28.280: E/AndroidRuntime(15294): java.lang.NullPointerException
10-30 01:13:28.280: E/AndroidRuntime(15294): at tricrose.gamedev.GameView.onDraw(GameView.java:56)
10-30 01:13:28.280: E/AndroidRuntime(15294): at tricrose.gamedev.GameThread.run(GameThread.java:30)
我有三个Java类:Game.java(Activity),GameView.java(SurfaceView)和GameThread.java(主线程)。
代码如下:
Game.java:
package tricrose.gamedev;
import android.os.Bundle;
import android.app.Activity;
import android.util.Log;
import android.view.KeyEvent;
import android.view.Menu;
import android.view.Window;
import android.view.WindowManager;
public class Game extends Activity {
public static final String TAG = Game.class.getSimpleName();
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
requestWindowFeature(Window.FEATURE_NO_TITLE);
getWindow().setFlags(WindowManager.LayoutParams.FLAG_FULLSCREEN, WindowManager.LayoutParams.FLAG_FULLSCREEN);
setContentView(new GameView(this));
Log.d(TAG, "View added");
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
getMenuInflater().inflate(R.menu.activity_game, menu);
return true;
}
}
GameView.java:
package tricrose.gamedev;
import android.app.Activity;
import android.content.Context;
import android.graphics.BitmapFactory;
import android.graphics.Canvas;
import android.graphics.Color;
import android.view.MotionEvent;
import android.view.SurfaceHolder;
import android.view.SurfaceView;
public class GameView extends SurfaceView implements SurfaceHolder.Callback {
public static final String TAG = GameView.class.getSimpleName();
private GameThread thread;
public GameView(Context context) {
super(context);
getHolder().addCallback(this);
thread = new GameThread(getHolder(), this);
setFocusable(true);
}
public void surfaceChanged(SurfaceHolder holder, int format, int width, int height) {
}
public void surfaceCreated(SurfaceHolder holder) {
thread.setRunning(true);
thread.start();
}
public void surfaceDestroyed(SurfaceHolder holder) {
boolean retry = true;
while (retry) {
try {
thread.join();
retry = false;
} catch (Exception e) {}
}
}
public boolean onTouchEvent(MotionEvent e) {
if (e.getAction() == MotionEvent.ACTION_DOWN) {
if (e.getY() > getHeight() - 60) {
thread.setRunning(false);
((Activity)getContext()).finish();
}
}
return super.onTouchEvent(e);
}
protected void onDraw(Canvas canvas) {
canvas.drawColor(Color.BLACK);
canvas.drawBitmap(BitmapFactory.decodeResource(getResources(), R.drawable.droid_1), 10, 10, null);
}
}
GameThread.java:
package tricrose.gamedev;
import android.graphics.Canvas;
import android.view.SurfaceHolder;
public class GameThread extends Thread {
public static final String TAG = GameThread.class.getSimpleName();
private boolean running;
private SurfaceHolder surfaceHolder;
private GameView gameView;
public GameThread(SurfaceHolder surfaceHolder, GameView gameView) {
super();
this.surfaceHolder = surfaceHolder;
this.gameView = gameView;
}
public void setRunning(boolean running) {
this.running = running;
}
public void run() {
Canvas canvas;
while (running) {
canvas = null;
try {
canvas = this.surfaceHolder.lockCanvas();
synchronized (surfaceHolder) {
this.gameView.onDraw(canvas);
}
} finally {
if (canvas != null) {
surfaceHolder.unlockCanvasAndPost(canvas);
}
}
}
}
}
我在互联网上搜索了一个解决方案,我找不到一个真正有用的解决方案,所以非常感谢任何帮助。
答案 0 :(得分:2)
我终于找到了解决方案!事实证明,在调用onDraw之前我应该检查画布是否为null,如果它为null,则通过完成活动退出应用程序。我在JavaCodeGeeks.com上找到了解决方案,在那里我看了一个Android教程。谢谢大家的所有答案!
答案 1 :(得分:0)
为什么你从onDraw和GameThread运行方法中的两个地方进行绘图。我认为你需要删除onDraw,只从GameThread rlun方法中删除每个绘图。
答案 2 :(得分:0)
这只是一个猜测,但是当应用程序尝试退出时,您的应用可能仍在绘制。在你的onDraw方法中,你调用这行代码(这可能是你的问题原因):
canvas.drawBitmap(BitmapFactory.decodeResource(getResources(), R.drawable.droid_1), 10, 10, null);
在这种情况下,您可能不再有可用的resuorces;)
您可以尝试:
1.将类私有位图变量放入GameView类:
private Bitmap mBitmap;
2.在GameView构造函数中加载位图:
mBitmap = BitmapFactory.decodeResource(getResources(), R.drawable.droid_1);
3.使用(已加载的)位图绘制:
canvas.drawBitmap(mBitmap, 10, 10, null);
希望有所帮助!