我做了一个例子，在 Android 的画布上扩展SurfaceView和Thread绘制一些对象，但我面临两个问题。
当按下后退按钮时，应用程序关闭，然后显示“不幸的是，您的示例已停止”。
当将方向从“Portrait”更改为“Landscape”或 VS 时，应用程序无法调整新屏幕并且不会更新绘图，然后它会崩溃并显示相同的消息“不幸的是，您的示例已停止”。
请查看代码：
@Override
public void surfaceChanged(SurfaceHolder holder, int format, int width,
int height) {
// TODO implement this method
holder.getSurface().setSize(width, height);
holder.setFormat(format);
}
@Override
public void surfaceCreated(SurfaceHolder holder) {
// at this point the surface is created and
// we can safely start the game loop
thread.setRunning(true);
thread.start();
}
@Override
public void surfaceDestroyed(SurfaceHolder holder) {
// tell the thread to shut down and wait for it to finish
// this is a clean shutdown
boolean retry = true;
while (retry) {
try {
thread.join();
retry = false;
} catch (InterruptedException e) {
// try again shutting down the thread
}
}
}
当我检查 logcat 时，我发现以下行表明这部分的问题
@Override
public void run() {
Canvas canvas;
// initialise timing elements for stat gathering
initTimingElements();
long beginTime; // the time when the cycle begun
long timeDiff; // the time it took for the cycle to execute
int sleepTime; // ms to sleep (<0 if we're behind)
int framesSkipped; // number of frames being skipped
sleepTime = 0;
while (running) {
canvas = null;
// try locking the canvas for exclusive pixel editing
// in the surface
try {
canvas = this.surfaceHolder.lockCanvas();
LoggerHandler.log("canvas : " + canvas);
synchronized (surfaceHolder) {
beginTime = System.currentTimeMillis();
framesSkipped = 0; // resetting the frames skipped
// update game state
this.gamePanel.update();
// render state to the screen
// draws the canvas on the panel
this.gamePanel.render(canvas);
// calculate how long did the cycle take
timeDiff = System.currentTimeMillis() - beginTime;
// calculate sleep time
sleepTime = (int) (FRAME_PERIOD - timeDiff);
if (sleepTime > 0) {
// if sleepTime > 0 we're OK
try {
// send the thread to sleep for a short period
// very useful for battery saving
Thread.sleep(sleepTime);
} catch (InterruptedException e) {
}
}
while (sleepTime < 0 && framesSkipped < MAX_FRAME_SKIPS) {
// we need to catch up
this.gamePanel.update(); // update without rendering
sleepTime += FRAME_PERIOD; // add frame period to check
// if in next frame
framesSkipped++;
}
// for statistics
framesSkippedPerStatCycle += framesSkipped;
// calling the routine to store the gathered statistics
storeStats();
}
} finally {
// in case of an exception the surface is not left in
// an inconsistent state
if (canvas != null) {
surfaceHolder.unlockCanvasAndPost(canvas);
}
} // end finally
}
}
这一行的问题：
canvas = this.surfaceHolder.lockCanvas();
null改变方向时返回。