为什么在通过VideoView播放视频之前屏幕无法清除？

Question

点击列表视图项目播放视频： 代码：

Intent intent = new Intent(E030.this, EPlayVideo.class);
Bundle b = new Bundle();
b.putString("File", dt.FileName);
intent.putExtras(b);
startActivity(intent);

EPlayVideo.java中的代码播放视频：

protected void onCreate(Bundle savedInstanceState) {
        // TODO Auto-generated method stub
        super.onCreate(savedInstanceState);
        setContentView(R.layout.layoutplayvideo);

        try {
            VideoView videoView = (VideoView) findViewById(R.id.videoView1);
            Intent outintent = getIntent();
            Bundle b = outintent.getExtras();
            String file = b.getString("File");
            MediaController mediaController = new MediaController(EPlayVideo.this);
            mediaController.setAnchorView(videoView);
            videoView.setMediaController(mediaController);
            videoView.setVideoPath(file);
            videoView.setRotation(90);
            videoView.start();

        } catch (Exception e) {
            // TODO: handle exception
        }

    }

结果：为什么在通过VideoView播放视频之前屏幕无法清除？