android - 恢复到 SurfaceView 显示黑屏

Question

一切正常，当我开始我的应用程序时。但是当我进入下一个 Activity 并返回 SurfaceView 时，它看起来像 black。当我调试时，我可以看到需要在 Canvas 上绘制的线条正在运行，但什么也没有显示。
这是我的代码:

public class DrawView extends SurfaceView implements Runnable
{

    Thread thread = null;
    SurfaceHolder holder;
    Bitmap background;
    Canvas canvas;
    Matrix matrixUP = new Matrix();
    Matrix matrixDOWN = new Matrix();
    boolean ok = false;

    public DrawView(Context context) 
    {
        super(context);
        holder = getHolder();
    }

    public void run() 
    {
        while(ok)
        {
            if(!holder.getSurface().isValid())
            {
                continue;
            }
            watch_hand = Bitmap.createScaledBitmap(watch_hand, width/4, height/6, false);
            watch_hand_down = Bitmap.createScaledBitmap(watch_hand_down, width/4, height/6, false);
            background = BitmapFactory.decodeResource(getResources(), R.drawable.needles);
            background = Bitmap.createScaledBitmap(background, width, height/2+20, false);
            canvas = holder.lockCanvas();
            matrixUP.setTranslate(CENTER_X - watch_hand.getWidth()/2, height/4 - watch_hand.getHeight() - 40);
            matrixUP.preRotate((float) degreUP , watch_hand.getWidth()/2 , watch_hand.getHeight()-10);

            matrixDOWN.setTranslate(CENTER_X - watch_hand_down.getWidth()/2, height/2 - watch_hand_down.getHeight() - 20);
            matrixDOWN.preRotate((float) degreDOWN , watch_hand_down.getWidth()/2 , 10);

            canvas.drawARGB(255, 255, 255, 255);
            canvas.drawBitmap(background, 0, 0, null);
            canvas.drawBitmap(watch_hand, matrixUP, null);
            canvas.drawBitmap(watch_hand_down, matrixDOWN, null);
            holder.unlockCanvasAndPost(canvas);
        }           
    }

    public void pause()
    {
        ok = false;
        while(true)
        {
            try
            {
                thread.join();
            }catch (InterruptedException e)
            {
                e.printStackTrace();
            }
            break;
        }
        thread = null;
    }

    public void resume()
    {
        ok = true;
        thread = new Thread(this);
        thread.start();
    }           
}

如您所见，我正在使用恢复和暂停功能。它们是从 onCreate 调用的。为什么会发生这种情况，我该如何解决？

谢谢!

Answer 1

答案取决于您如何更改为其他 Activity 。

基本上，您必须考虑如何在 Activity 暂停、停止或销毁时存储 Surface 的当前状态。

例如，您可以在 Activity 中重载 onSaveInstanceState 以保存 degreUP 和 degreDOWN(顺便说一下，它们未在当前代码 fragment 中定义)。并在 onRestoreInstanceState 中恢复它们。见Saving Android Activity state using Save Instance State