表面支架上的凸轮图片，绘制：由于表面类型而出现异常

Question

我使用 SurfaceView 和 SurfaceHolder 在我的测试应用中开始相机预览。

public class TextLocatorActivity extends Activity {

    private Preview pvw;

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        requestWindowFeature(Window.FEATURE_NO_TITLE);
        this.getWindow().setFlags(WindowManager.LayoutParams.FLAG_FULLSCREEN, WindowManager.LayoutParams.FLAG_FULLSCREEN);

        pvw = new Preview(this);
        setContentView(pvw);        
    }   

我想使用 CameraPreview（随 SDK 版本 7 的 SDK 示例一起提供）。单击 UI 即可拍摄照片。这是 Preview 类：

public class Preview extends SurfaceView implements OnClickListener, SurfaceHolder.Callback {

SurfaceHolder holder;
Camera cam; 

final static String TAG = "TextLocator:Preview";

Preview(Context context) {
    super(context);

    holder = getHolder();
    holder.addCallback(this);
    this.setOnClickListener(this);
    // seems to be required (although the docs state, this enum is deprecated, as the type will be chosen automatically...
    holder.setType(SurfaceHolder.SURFACE_TYPE_PUSH_BUFFERS);
}

public void surfaceCreated(SurfaceHolder holder) {
    cam = Camera.open();
    try {
        Camera.Parameters params = cam.getParameters();
        params.set("orientation", "landscape");
        Camera.Size bestSize = getBestPreviewSize(480, 320);
        params.setPreviewSize(bestSize.width, bestSize.height);
        cam.setParameters(params);
        // where to draw:
        cam.setPreviewDisplay(holder);
    } catch (IOException exception) {
        cam.release();
        cam = null;
        // TODO: add more exception handling logic here
    }
}

private Camera.Size getBestPreviewSize(int width, int height)
{
    // checks for supported sizes close to the demanded values - implemented.
}


public void surfaceDestroyed(SurfaceHolder holder) {
    cam.stopPreview();
    cam.release();
    cam = null;
}

public void surfaceChanged(SurfaceHolder holder, int format, int w, int h) {
    Camera.Parameters parameters = cam.getParameters();
    parameters.setPreviewSize(w, h);

    cam.setParameters(parameters);
    cam.startPreview();
}

Camera.PictureCallback picCallback = new Camera.PictureCallback() {

    public void onPictureTaken(byte[] bytes, Camera arg1) {
        synchronized(holder) {
                Canvas c = null;    

                try {
                    c = holder.lockCanvas();                

                    Paint paint = new Paint();
                    paint.setAntiAlias(false);
                    paint.setARGB(200, 120, 180, 0);

                    c.drawLine(10, 10, c.getWidth() - 10, c.getHeight() - 10, paint);
                }
                catch (Exception e) {
                    Log.d(TAG, "Exception: " + e.getMessage());
                    // IllegalArguementException Surface Type is SURFACE_TYPE_PUSH_BUFFERS
                }
                finally {       
                    holder.unlockCanvasAndPost(c);  
                }
            }
    }
};

public void onClick(View v) 
{
    cam.takePicture(null, null, picCallback);    
}

}

接下来，我尝试对 SurfaceHolder 的相应 Canvas 进行一些额外的绘制。因此我调用 canvas =holder.lockCanvas()。这将导致 IllegalArgumentException 并显示以下消息：

Surface type is SURFACE_TYPE_PUSH_BUFFERS

现在，文档指出这些表面类型已被弃用，设置的值将被忽略。但是，只有当我将类型设置为该特定值时，相机预览才有效。

如何实现在显示拍摄照片的 SurfaceView 的 Canvas 上绘图？或者应该将其放在不同的图层/视图上？

Answer 1

您无法同时显示相机预览和使用画布进行绘制。你必须做其中之一。