android视频播放的问题


<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent"
    android:orientation="vertical" >
    <VideoView android:name="@+id/video"
         android:layout_width="fill_parent"
         android:layout_height="fill_parent"/></LinearLayout>  private VideoView video;
    private MediaController ctrl;
private List<Map<String, String>> list;
    protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
//设置窗口特征
getWindow().setFormat(PixelFormat.TRANSLUCENT);
setContentView(R.layout.mp4);
list=publicState.list;
video=(VideoView)findViewById(R.id.video);
int i=getIntent().getIntExtra("position", 0);
File file=new File(list.get(i).get("path"));
if(file.exists()){
Log.i("tag", video+"----------->"+file.getAbsolutePath());
video.setVideoPath(file.getAbsolutePath());
ctrl=new MediaController(this);
ctrl.setMediaPlayer(video);
video.setMediaController(ctrl);
video.requestFocus();
}
}包空指针异常，log打印出来，video是null；这是怎么回事呀android  视频播放