如何处理这个线程？

Question

在我的应用程序中，有一个线程在调用活动 A 时运行。现在我要去另一个活动 B 对那个线程什么都不做。 活动 B 上还有另一个线程。 现在在完成活动 B 的活动之后。我回到活动 A。

当时我收到错误消息，活动 A 上的线程已经在运行。 那么，我应该怎么做才能处理这个错误？？？ 每次我从活动 B 回到活动 A 时，我的应用程序都会崩溃。

谢谢。

在此错误日志中，绘图表面是我的活动 A，如上所述。 错误日志：

11-10 15:08:24.730: ERROR/AndroidRuntime(1145): FATAL EXCEPTION: main
11-10 15:08:24.730: ERROR/AndroidRuntime(1145): java.lang.IllegalThreadStateException: Thread already started.
11-10 15:08:24.730: ERROR/AndroidRuntime(1145):     at java.lang.Thread.start(Thread.java:1322)
11-10 15:08:24.730: ERROR/AndroidRuntime(1145):     at com.example.drawing.DrawingSurface.surfaceCreated(DrawingSurface.java:113)
11-10 15:08:24.730: ERROR/AndroidRuntime(1145):     at android.view.SurfaceView.updateWindow(SurfaceView.java:532)
11-10 15:08:24.730: ERROR/AndroidRuntime(1145):     at android.view.SurfaceView.onWindowVisibilityChanged(SurfaceView.java:206)
11-10 15:08:24.730: ERROR/AndroidRuntime(1145):     at android.view.View.dispatchWindowVisibilityChanged(View.java:3891)
11-10 15:08:24.730: ERROR/AndroidRuntime(1145):     at android.view.ViewGroup.dispatchWindowVisibilityChanged(ViewGroup.java:719)
11-10 15:08:24.730: ERROR/AndroidRuntime(1145):     at android.view.ViewGroup.dispatchWindowVisibilityChanged(ViewGroup.java:719)
11-10 15:08:24.730: ERROR/AndroidRuntime(1145):     at android.view.ViewGroup.dispatchWindowVisibilityChanged(ViewGroup.java:719)
11-10 15:08:24.730: ERROR/AndroidRuntime(1145):     at android.view.ViewGroup.dispatchWindowVisibilityChanged(ViewGroup.java:719)
11-10 15:08:24.730: ERROR/AndroidRuntime(1145):     at android.view.ViewRoot.performTraversals(ViewRoot.java:744)
11-10 15:08:24.730: ERROR/AndroidRuntime(1145):     at android.view.ViewRoot.handleMessage(ViewRoot.java:1727)
11-10 15:08:24.730: ERROR/AndroidRuntime(1145):     at android.os.Handler.dispatchMessage(Handler.java:99)
11-10 15:08:24.730: ERROR/AndroidRuntime(1145):     at android.os.Looper.loop(Looper.java:123)
11-10 15:08:24.730: ERROR/AndroidRuntime(1145):     at android.app.ActivityThread.main(ActivityThread.java:4627)
11-10 15:08:24.730: ERROR/AndroidRuntime(1145):     at java.lang.reflect.Method.invokeNative(Native Method)
11-10 15:08:24.730: ERROR/AndroidRuntime(1145):     at java.lang.reflect.Method.invoke(Method.java:521)
11-10 15:08:24.730: ERROR/AndroidRuntime(1145):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:868)
11-10 15:08:24.730: ERROR/AndroidRuntime(1145):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:626)
11-10 15:08:24.730: ERROR/AndroidRuntime(1145):     at dalvik.system.NativeStart.main(Native Method)

出现错误的 DrawingSurface 类：

public class DrawingSurface extends SurfaceView implements SurfaceHolder.Callback {
private Boolean _run;
protected DrawThread thread;
public Canvas canvas = null;
private CommandManager commandManager;
//private Bitmap myBitmap;
private Bitmap mBitmap;

public DrawingSurface(Context context, AttributeSet attrs) {
    super(context, attrs);

    getHolder().addCallback(this);

    commandManager = new CommandManager();
    thread = new DrawThread(getHolder());
}

class DrawThread extends Thread{
    private SurfaceHolder mSurfaceHolder;

    public DrawThread(SurfaceHolder surfaceHolder){
        mSurfaceHolder = surfaceHolder;

    }

    public void setRunning(boolean run) {
        _run = run;
    }

    @Override
    public void run() {
        //Canvas canvas = null;
        while (_run){

            try{
                canvas = mSurfaceHolder.lockCanvas(null);
                if(mBitmap == null){
                    mBitmap =  Bitmap.createBitmap (1, 1, Bitmap.Config.ARGB_8888);
                }

                final Canvas c = new Canvas (mBitmap);
                //canvas.drawColor(0, PorterDuff.Mode.CLEAR);
                c.drawColor(0, PorterDuff.Mode.CLEAR);
                canvas.drawColor(Color.WHITE); 
//             Bitmap kangoo =   BitmapFactory.decodeResource(getResources(),R.drawable.icon);

                if(!(DrawingActivity.imagePath==null)){
                    c.drawBitmap(DrawingActivity.mBitmap, 0, 0, null);
                }
                commandManager.executeAll(c);
                canvas.drawBitmap (mBitmap, 0,  0,null);
            } finally {

                mSurfaceHolder.unlockCanvasAndPost(canvas);
            }
        }

    }
}


public void addDrawingPath (DrawingPath drawingPath){
    commandManager.addCommand(drawingPath);
}

public boolean hasMoreRedo(){
    return commandManager.hasMoreRedo();
}

public void redo(){
    commandManager.redo();
}

public void undo(){
    commandManager.undo();
}

public boolean hasMoreUndo(){
    return commandManager.hasMoreRedo();
}

public Bitmap getBitmap(){
    return mBitmap;
}


public void surfaceChanged(SurfaceHolder holder, int format, int width,  int height) {
    // TODO Auto-generated method stub
    mBitmap =  Bitmap.createBitmap (width, height, Bitmap.Config.ARGB_8888);;
}

public void surfaceCreated(SurfaceHolder holder) {
    // TODO Auto-generated method stub
        thread.setRunning(true);
        thread.start(); // error at this line
        if(!thread.isAlive())            
             thread.start();  
}

public void surfaceDestroyed(SurfaceHolder holder) {
    // TODO Auto-generated method stub
    boolean retry = true;
    thread.setRunning(false);
    while (retry) {
        try {
            thread.join();
            retry = false;
        } catch (InterruptedException e) {
            // we will try it again and again...
        }
    }
}

}

Answer 1

如果您使用AsyncTask，而不是使用Thread 和Runnable，它们会在您离开活动后自动关闭。

或者，如果您只想使用Thread，则必须使用t.interrupt() 停止任何正在运行的Thread t，然后再离开活动。

所以，我想将t.interrupt() 放入活动的onPause() 方法中以停止Thread

编辑：这一行是多余的

if(!thread.isAlive())            
             thread.start();  

我不明白你想用这个做什么，

thread.setRunning(true);

这可能会造成一些问题，删除它并重试

即试试这个

public void surfaceCreated(SurfaceHolder holder) {
    // TODO Auto-generated method stub
        thread.start(); // error at this line 
}

Answer 2

这不起作用（大部分时间 -> 竞争条件）：

   thread.start(); // error at this line
   if(!thread.isAlive()) thread.start();

不要那样做。一个线程只能启动一次，并且绝对没有理由重新尝试启动它。

thread.start(); 确实是您启动线程所需的全部内容。

编辑：

while (retry) {
  thread.join();
  retry = false;
}

没有任何意义。只需join() 并可能将中断转发给您的thread。