我正在为 Android 2.2+ 开发简单的视频录制应用程序，并且无法让 Timer 线程按预期工作。代码如下，所以步骤是：
- 当用户按下开始录制按钮时，录制开始并调用fightTimer.start() 方法。
- 它调用 timer.start() 方法开始运行线程。timer是fightTimer里面的线程对象
- 当用户单击停止按钮时，fightTimer 方法 stop() 被调用。在那里我设置了一个标志 stopTimer=true 以便停止线程方法运行并调用 timer.wait() 方法以便线程等待
- 当用户单击开始录制按钮时，再次调用fightTimer.start() 方法。它调用线程 timer.start() 因为计时器已经启动但是它抛出异常。
- 我捕获异常并调用fightTimer.restart() 方法。这个方法将我在步骤 3 中设置的标志 stopTimer 设置为 true，所以现在我们有 stopTimer=true。计时器线程仍在 run() 方法内部等待
- 然后它调用 timer.notify() 让 timer 知道它不需要再等待并且可以继续运行
- 现在我期待计时器线程再次开始运行，但由于某种原因，此时执行跳转到调用 notify() (restart()) 并设置标志 stopTimer=false 的同一方法的开头，然后尝试通知计时器线程再次。它抛出运行时异常，这就是它结束的地方。
我认为我对线程整体同步的理解是不正确的，所以如果有人能指出我在哪里搞砸了，那就太好了。下面是 FightTimeris 的代码，我什至没有在 logCat 中获得任何输出信息。就像我说的任何帮助将不胜感激，因为我不明白为什么会发生这种情况以及如何解决它。
public class FightTimer extends SurfaceView implements Runnable, SurfaceHolder.Callback {
public Thread timer;
public SurfaceHolder surfaceHolder;
public Canvas canvas;
public int counter=0;
public volatile boolean stopTimer=false;
public volatile boolean pauseTimer=false;
public FightTimer(Context context)
{
super(context);
surfaceHolder=getHolder();
// this is necessary to make surfaceview transparent
surfaceHolder.setFormat(PixelFormat.TRANSLUCENT);
setZOrderOnTop(true);
surfaceHolder.addCallback(this);
timer=new Thread(this);
}
public void start()
{
try
{
timer.start();
}
catch(IllegalThreadStateException ex)
{
reStart();
}
}
public synchronized void reStart()
{
// here the method is executed twice as I described in step 7
// after notify() it actually jumps back to stopTimer=false again and then exits the function. Then outside of this object I catch RuntimeException
stopTimer=false;
timer.notify();
}
public synchronized void pause()
{
pauseTimer=true;
}
public synchronized void resume()
{
pauseTimer=false;
timer.notify();
}
public void stop()
{
stopTimer=true;
}
public void run() {
TimeWatch timeWatch=TimeWatch.start();
Paint paint=new Paint();
paint.setColor(Color.RED);
paint.setTypeface(Typeface.create("Arial",Typeface.NORMAL));
paint.setTextSize(20);
while(true)
{
// this is to pause timer
try
{
if(pauseTimer)
{
synchronized(timer) {
while(pauseTimer)
timer.wait();
}
// TODO heres the code should be executed when timer is resumed eg.
// maybe calculate how timer should count now as it wasn't counting for a while etc
}
} catch(InterruptedException ex)
{
}
// this is to pause timer
try
{
if(stopTimer)
{
synchronized(timer) {
while(stopTimer)
timer.wait();
}
// TODO heres the code should be executed when timer is restarted
// maybe reset timer completely etc
timeWatch.reset();
}
} catch(InterruptedException ex)
{
}
canvas=surfaceHolder.lockCanvas();
// canvas might not exists at this point as we might be in activitis onStop() callback and stopping preview
// etc. so we need to check if so then we exit run function
if(canvas==null) return;
//canvas.drawARGB(0,255,255,255);
canvas.drawColor(0, android.graphics.PorterDuff.Mode.CLEAR);
long minutes=timeWatch.time(TimeUnit.SECONDS)/60;
canvas.drawText(counter+" "+minutes+":"+timeWatch.time(TimeUnit.SECONDS)%60,0,counter%60, paint);
counter++;
surfaceHolder.unlockCanvasAndPost(canvas);
}
}
public void surfaceChanged(SurfaceHolder holder, int format, int width,
int height) {
// TODO Auto-generated method stub
//Toast.makeText(getContext(), "Surface Changed", Toast.LENGTH_LONG).show();
}
public void surfaceCreated(SurfaceHolder holder) {
// TODO Auto-generated method stub
//timer.start();
}
public void surfaceDestroyed(SurfaceHolder holder) {
// TODO Auto-generated method stub
// when surface is destroyed it means it cannot be displayed anymore and there is no canvas to draw
// meaning the run() method cannot draw anything and calls to surfaceHolder will throw exception
// so we need to stop thread here
// this will happen when activity is in onStop() callback and when is already invisible and we are going to
// remove the object anyway so we don't care what will happenn later and make it wait. All we need is stop
// run() from calling any other methods on canvas from surfaceHolder
Toast.makeText(getContext(), "Surface Destroyed", Toast.LENGTH_LONG).show();
}
public void setSurfaceHolder(SurfaceHolder surfaceHolder2) {
// TODO Auto-generated method stub
surfaceHolder=surfaceHolder2;
}
}
另请参阅 restart() 方法中的编辑评论。下面是调用堆栈，当 restart() 方法退出时。如果需要更多信息，请告诉我。
DalvikVM[localhost:8754]
Thread [<1> main] (Suspended)
<VM does not provide monitor information>
MyFirstAppActivity.startRecording(View) line: 271
Method.invokeNative(Object, Object[], Class, Class[], Class, int, boolean) line: not available [native method]
Method.invoke(Object, Object...) line: 521
View$1.onClick(View) line: 2077
Button(View).performClick() line: 2461
View$PerformClick.run() line: 8888
ViewRoot(Handler).handleCallback(Message) line: 587
ViewRoot(Handler).dispatchMessage(Message) line: 92
Looper.loop() line: 123
ActivityThread.main(String[]) line: 4627
Method.invokeNative(Object, Object[], Class, Class[], Class, int, boolean) line: not available [native method]
Method.invoke(Object, Object...) line: 521
ZygoteInit$MethodAndArgsCaller.run() line: 858
ZygoteInit.main(String[]) line: 616
NativeStart.main(String[]) line: not available [native method]
Thread [<7> Binder Thread #2] (Running)
Thread [<6> Binder Thread #1] (Running)
Thread [<8> Binder Thread #3] (Running)
Thread [<9> Thread-9] (Running)