UI在挂锁后在线程中休眠后挂起

Question

I´m trying to implement a fractal renderer on android. It uses a SurfaceView to display the results.

I use a seperate Thread for rendering to keep the UI working during processing, but it locks up until unlockCanvasAndPost is called. Is this the expected behavior? How can I keep the UI from locking up? In this example I simulate the long processing by Thread.sleep.

My SurfaceView-Class looks like this:

public class MyView extends SurfaceView implements SurfaceHolder.Callback {

RenderThread rt = null;

public MyView(Context context, AttributeSet attrs) {
    super(context, attrs);
    getHolder().addCallback(this);
}

@Override
public void surfaceChanged(SurfaceHolder holder, int format, int width,
        int height) {
}

@Override
public void surfaceCreated(SurfaceHolder holder) {
    // TODO Auto-generated method stub
    rt = new RenderThread(holder);
    rt.start();
}

@Override
public void surfaceDestroyed(SurfaceHolder holder) {
    rt.setStop();       
}
}

And this is the RenderThread-class:

public class RenderThread extends Thread {
SurfaceHolder holder;
boolean running = true;

public RenderThread(SurfaceHolder holder) {
    this.holder = holder;       
}

public void setStop() {
    running = false;
}

@Override
public void run() {
    while(running) {
        Canvas canvas = holder.lockCanvas();

        try {
            Thread.sleep(2000);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        if(canvas == null) return;

        Paint p = new Paint();
        p.setARGB(255, 255, 0, 0);
        canvas.drawLine(0, 0, 100, 100, p);
        holder.unlockCanvasAndPost(canvas);
    }
}
}

Answer 1

Several possibilities.

You don't show how you've incorporated your MyView class into the activity that contains it. Because you've subclassed SurfaceView, you have to add code to your activity to specifically deal with what you've added with RenderThread. The activity's onPause() method, for example, should be sending a signal to your MyView class to stop its RenderThread.

The surfaceDestroyed() method gets called just before the SurfaceHolder's surface is destroyed. You cannot return from that method until your RenderThread has stopped touching it. This is accomplished through synchronization. Official Android documentation for surfaceDestroyed() .

There's a terrific example of how all of this is properly done in WindowSurface.java in the ApiDemos project (for Eclipse, installed with "Samples for SDK" via the Android SDK Manager). Once you've loaded the project into Eclipse (with File->New->Project->Android Sample Project), find WindowSurface.java in com.example.android.apis.graphics within the project.

Finally, if your actual code in the thread's run method (what you've replaced with Thread.sleep in the interest of brevity here) does anything with the canvas then your check for canvas==null should be immediately below the attempted locking of that canvas. Ideally, it's better form to do that anyway.