CameraPreview 添加时间水印

要在 CameraPreview 中添加时间水印，可以使用 SurfaceView 来预览摄像头，并在 SurfaceView 上绘制时间水印。以下是一个简单的示例：

1. 在布局文件中添加一个 SurfaceView 元素，用于显示摄像头预览和录制的视频：

<SurfaceView
    android:id="@+id/surfaceView"
    android:layout_width="match_parent"
    android:layout_height="match_parent" />

2. 在 CameraPreview 类中获取 SurfaceView，并设置它作为 Camera 的预览：

public class CameraPreview extends SurfaceView implements SurfaceHolder.Callback {
    private Camera mCamera;

    public CameraPreview(Context context, Camera camera) {
        super(context);
        mCamera = camera;

        // Install a SurfaceHolder.Callback so we get notified when the
        // underlying surface is created and destroyed.
        SurfaceHolder holder = getHolder();
        holder.addCallback(this);
    }

    public void surfaceCreated(SurfaceHolder holder) {
        // The Surface has been created, now tell the camera where to draw the preview.
        try {
            mCamera.setPreviewDisplay(holder);
            mCamera.startPreview();
        } catch (IOException e) {
            Log.d(TAG, "Error setting camera preview: " + e.getMessage());
        }
    }

    public void surfaceDestroyed(SurfaceHolder holder) {
        // empty. Take care of releasing the Camera preview in your activity.
    }

    public void surfaceChanged(SurfaceHolder holder, int format, int w, int h) {
        // If your preview can change or rotate, take care of those events here.
        // Make sure to stop the preview before resizing or reformatting it.
        if (holder.getSurface() == null){
          // preview surface does not exist
          return;
        }

        // stop preview before making changes
        try {
            mCamera.stopPreview();
        } catch (Exception e){
          // ignore: tried to stop a non-existent preview
        }

        // set preview size and make any resize, rotate or
        // reformatting changes here

        // start preview with new settings
        try {
            mCamera.setPreviewDisplay(holder);
            mCamera.startPreview();
        } catch (Exception e){
            Log.d(TAG, "Error starting camera preview: " + e.getMessage());
        }
    }
}

3. 在 SurfaceView 上绘制时间水印，可以在 SurfaceView 的回调方法 surfaceChanged() 中获取 Canvas 对象，并在其中绘制水印：

private void drawTimeWatermark(Canvas canvas) {
    Paint paint = new Paint();
    paint.setColor(Color.WHITE);
    paint.setTextSize(50);
    canvas.drawText(getCurrentTime(), 100, 100, paint);
}

private String getCurrentTime() {
    SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
    return sdf.format(new Date());
}

public void surfaceChanged(SurfaceHolder holder, int format, int w, int h) {
    if (holder.getSurface() == null){
        return;
    }

    try {
        mCamera.stopPreview();
    } catch (Exception e){
        // ignore: tried to stop a non-existent preview
    }

    try {
        mCamera.setPreviewDisplay(holder);
        mCamera.startPreview();

        Canvas canvas = holder.lockCanvas();
        drawTimeWatermark(canvas);
        holder.unlockCanvasAndPost(canvas);
    } catch (Exception e){
        Log.d(TAG, "Error starting camera preview: " + e.getMessage());
    }
}

这样就可以在 CameraPreview 中添加时间水印了。当然，还可以通过调整 Paint 对象的属性来改变水印的样式。