NullpointerException在进度条的AsyncTask的onPreExcute

Question

我有一个NullPointerException当我尝试设置ProgessBar在onPreExecute AsyncTask (mProgressBar.setVisibility(View.VISIBLE);)中可见。我不知道哪里出了问题！谢谢大家！

<ProgressBar 
    android:id="@+id/pb_featured_game_progress" 
    android:layout_width="wrap_content" 
    android:layout_height="wrap_content" 
    android:visibility="gone" 
    /> 

---

public class MainActivity extends Activity { 

... 
private ProgressBar mProgressBar; 



@Override 
protected void onCreate(Bundle savedInstanceState) { 

new FetchGamesTask().execute(); 


private class FetchGamesTask extends 
     AsyncTask<Integer, Integer, List<GameInfo>> { 


    @Override 
    protected void onPreExecute() { 
     // TODO Auto-generated method stub 

     super.onPreExecute(); 

     mProgressBar = (ProgressBar)findViewById(R.id.pb_featured_game_progress); 
     mProgressBar.setVisibility(View.VISIBLE); 
    } 

Answer 1

在打电话之前，您FetchGamesTask的执行，你应该用XML文件中的主视图关联。

像这样

protected void onCreate(Bundle savedInstanceState) { 
// the OS will inflate the main_activity.xml 
// file and use it for this activity 
setContentView(R.layout.main_activity); 
new FetchGamesTask().execute();