我想在我的Android应用程序中制作一些水涟漪，所以我使用这个javascript代码http://jsfiddle.net/esteewhy/5Ht3b/6/转换为C代码，就像它显示在Live Wallpaper Water Ripple Effect（由esteewhy）。
我有一个主要活动，点击按钮后调用水波纹活动。我的可变位图水波纹很好用，问题是当我点击Android设备的“后退”按钮时，系统崩溃抛出这个错误：
FATAL EXCEPTION: Thread-2556
java.lang.NullPointerException
at com.wheelly.whater.WaterView.onDraw (line 149)
at com.wheelly.whater.WaterView$GameThread.run (line 255)
我想处理Thread或活动本身存在一些问题。
以下是水涟漪的代码：
public class WaterView extends SurfaceView implements SurfaceHolder.Callback {
GameThread thread;
public static Bitmap icon;
//Measure frames per second.
long now;
int framesCount=0;
int framesCountAvg=0;
long framesTimer=0;
Paint fpsPaint=new Paint();
//Frame speed
long timeNow;
long timePrev = 0;
long timePrevFrame = 0;
long timeDelta;
private int width = 480;
private int height = 800;
private short riprad = 6;
boolean flip;
private short[] ripplemap, last_map;
Bitmap ripple;
private static final String TAG = null;
private Rippler rippler;
public WaterView(Context context) {
super(context);
initialize();
}
void initialize() {
//CB
icon = BitmapFactory.decodeResource(getResources(), R.drawable.sand100);
icon = convertToMutable(icon);
//--
rippler = new NativeRippler();
reinitgGlobals();
fpsPaint.setTextSize(30);
//Set thread
getHolder().addCallback(this);
setFocusable(true);
}
void reinitgGlobals() {
int size = width * (height + 2) * 2;
ripplemap = new short[size];
last_map = new short[size];
Bitmap texture = createBackground(width, height); // this creates a MUTABLE bitmap
ripple = texture;
_td = new int[width * height];
texture.getPixels(_td, 0, width, 0, 0, width, height);
_rd = new int[width * height];
}
void randomizer() {
final Random rnd = new Random();
final Handler disHAndler = new Handler();
final Runnable disturbWater = new Runnable() {
@Override
public void run() {
disturb(rnd.nextInt(width), rnd.nextInt(height));
disHAndler.postDelayed(this, 7000);
}
};
disHAndler.post(disturbWater);
}
private static Bitmap createBackground(int width, int height) {
Canvas cb = new Canvas (icon);
cb.save();
cb.restore();
return icon;
}
private Bitmap convertToMutable(Bitmap bitmap) {
try {
File file = new File("/mnt/sdcard/sample/temp.txt");
file.getParentFile().mkdirs();
RandomAccessFile randomAccessFile = new RandomAccessFile(file, "rw");
int width_mutable = bitmap.getWidth();
int height_mutable = bitmap.getHeight();
FileChannel channel = randomAccessFile.getChannel();
MappedByteBuffer map = channel.map(MapMode.READ_WRITE, 0, width_mutable*height_mutable*4);
bitmap.copyPixelsToBuffer(map);
bitmap.recycle();
bitmap = Bitmap.createBitmap(width_mutable, height_mutable, Config.ARGB_8888);
map.position(0);
bitmap.copyPixelsFromBuffer(map);
channel.close();
randomAccessFile.close();
} catch (FileNotFoundException e) {
Log.i(TAG, "::onActivityResult:" + ""+Log.getStackTraceString(e));
} catch (IOException e) {
Log.i(TAG, "::onActivityResult:" + ""+Log.getStackTraceString(e));
}
return bitmap;
}
@Override
protected void onSizeChanged(int w, int h, int oldw, int oldh) {
super.onSizeChanged(w, h, oldw, oldh);
width = w;
height = h;
reinitgGlobals();
}
@Override
protected void onDraw(android.graphics.Canvas canvas) {
super.onDraw(canvas);
newframe();
canvas.drawBitmap(ripple, 0, 0, null);
//Measure frame rate (unit: frames per second).
now=System.currentTimeMillis();
canvas.drawText(framesCountAvg+" fps", 40, 70, fpsPaint);
framesCount++;
if(now-framesTimer>1000) {
framesTimer=now;
framesCountAvg=framesCount;
framesCount=0;
}
}
/**
* Disturb water at specified point
*/
private void disturb(int dx, int dy) {
rippler.disturb(dx, dy, width, height, riprad, ripplemap, flip);
}
int[] _td;
int[] _rd;
/**
* Generates new ripples
*/
private void newframe() {
System.arraycopy(_td, 0, _rd, 0, width * height);
flip = !flip;
rippler.transformRipples(height, width, ripplemap, last_map, _td, _rd, flip);
ripple.setPixels(_rd, 0, width, 0, 0, width, height);
}
@Override
public synchronized boolean onTouchEvent(MotionEvent event) {
disturb((int)event.getX(), (int)event.getY());
return true;
}
@Override
public void surfaceChanged(SurfaceHolder arg0, int arg1, int arg2, int arg3) {
}
@Override
public void surfaceCreated(SurfaceHolder arg0) {
thread = new GameThread(getHolder(), this);
thread.setRunning(true);
thread.start();
}
@Override
public void surfaceDestroyed(SurfaceHolder arg0) {
boolean retry = true;
thread.setRunning(false);
while (retry) {
try {
thread.join();
retry = false;
} catch (InterruptedException e) {
}
}
}
class GameThread extends Thread {
private SurfaceHolder surfaceHolder;
private WaterView gameView;
private boolean run = false;
public GameThread(SurfaceHolder surfaceHolder, WaterView gameView) {
this.surfaceHolder = surfaceHolder;
this.gameView = gameView;
}
public void setRunning(boolean run) {
this.run = run;
}
public SurfaceHolder getSurfaceHolder() {
return surfaceHolder;
}
@Override
public void run() {
Canvas c;
while (run) {
c = null;
//limit frame rate to max 60fps
timeNow = System.currentTimeMillis();
timeDelta = timeNow - timePrevFrame;
if ( timeDelta < 16) {
try {
Thread.sleep(16 - timeDelta);
}
catch(InterruptedException e) {
}
}
timePrevFrame = System.currentTimeMillis();
try {
c = surfaceHolder.lockCanvas(null);
synchronized (surfaceHolder) {
//call methods to draw and process next fame
gameView.onDraw(c);
}
} finally {
if (c != null) {
surfaceHolder.unlockCanvasAndPost(c);
}
}
}
}
}
}
答案 0 :(得分：2)
我找到了解决方案：
我不得不在活动的onPause方法中中断线程，而不是在onStop方法中执行它。现在它运作正常。
非常感谢大家帮助我解决这个问题。
答案 1 :(得分：1)
你应该在方法Activity.onStop
中关闭你的工作线程 @Override
protected void onStop() {
thread.interrupt();
super.onStop();
}
在GameThread的run方法中，在调用gameView.onDraw（c）之前检查线程是否被中断;像这样：
if(isInterrupted()) {
break;
}
gameView.onDraw(c);
答案 2 :(得分：1)
不要直接在视图上调用onDraw，而是调用gameView.invalidate()
synchronized (surfaceHolder) {
//call methods to draw and process next fame
gameView.invalidate();
}
如果它不起作用，请尝试使用带有断点的调试器来查看哪个变量完全为空