您必须调用ProgressDialog秀上preExecute AsyncTasks（）（）方法。例如：

 类MyTask扩展的AsyncTask＆LT;太虚，太虚，太虚＆GT; {
 ProgressDialog PD;
    @覆盖
    在preExecute保护无效（）{
      super.on preExecute（）;
       PD =新ProgressDialog（MainActivity.this）;
       pd.setMessage（装载）;
       pd.show（）;
    }    @覆盖
    保护无效doInBackground（虚空...... PARAMS）{
      //做你的要求
    }    @覆盖
    保护无效onPostExecute（虚空结果）{
      super.onPostExecute（结果）;
      如果（PD！= NULL）
      {
         pd.dismiss（）;
      }
    }
  }
 

I'm trying to show a progress dialog while the twitter feed is loading up...However the progress dialog remains on screen when the twitter feed appears. Any help is much appreciated.

public class MainActivity extends ListActivity {

    final static String twitterScreenName = "CFABUK";
    final static String TAG = "MainActivity";
    private AsyncTask<Object, Void, ArrayList<TwitterTweet>> tat;
    boolean done;

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        done=false;
        AndroidNetworkUtility androidNetworkUtility = new AndroidNetworkUtility();
        if (androidNetworkUtility.isConnected(this)) {
            TwitterAsyncTask syn=new TwitterAsyncTask();
            syn.execute(twitterScreenName,this);


            ProgressDialog pd = new ProgressDialog(MainActivity.this);
            pd.setMessage("loading");
            pd.show();

            do {
                if(!(syn.getStatus()==AsyncTask.Status.RUNNING)) {
                pd.dismiss();
                pd.cancel();
                done=true;
                }
            } while(done=false);


        } else {
            Log.v(TAG, "Network not Available!");
        }
    }
}

You must call ProgressDialog show() method on AsyncTasks onPreExecute(). For example:

class MyTask extends AsyncTask<Void, Void, Void> {
 ProgressDialog pd;
    @Override
    protected void onPreExecute() {
      super.onPreExecute();
       pd = new ProgressDialog(MainActivity.this);
       pd.setMessage("loading");
       pd.show();
    }

    @Override
    protected Void doInBackground(Void... params) {
      // Do your request
    }

    @Override
    protected void onPostExecute(Void result) {
      super.onPostExecute(result);
      if (pd != null)
      {
         pd.dismiss();
      }
    }
  }