我第一次调用Android相机时整个屏幕变黑了

Question

我第一次使用此代码调用相机时，

    mCamera = getCameraInstance();  // Create an instance of Camera
    // Create our Preview view and set it as the content of our activity.
    mPreview = new CameraPreview(this, mCamera);// Create our Preview view and set it as the content of our activity.
    FrameLayout preview = (FrameLayout) findViewById(R.id.quest_image);
    preview.addView(mPreview);

整个屏幕变暗一会儿，然后预览屏幕显示预览。所有其他电话只有预览屏幕闪烁黑色，然后显示预览。即使在第一次通话时我的预览屏幕是如何闪现黑的？感谢