ProgressDialog不會顯示，直到它太遲

Question

我正在寫一個活動，它通過HTTP從Web獲取一些XML，然後將其解析爲一個DOM。然後它從DOM中提取一些必需的數據。

您可以想象，這需要一些時間，因此我將該代碼放入它自己的線程中，然後嘗試設置ProgressDialog以在用戶等待完成時顯示。

問題是ProgressDialog根本不顯示。如果我刪除電話解僱（），那麼它顯示的工作完成之後，很明顯，只是坐在那裏......

這裏是我的代碼：

@Override 
public void onCreate(Bundle savedInstanceState) { 
    super.onCreate(savedInstanceState); 
    progressDialog = ProgressDialog.show(this, "", "Loading...", true); 
    Thread downloadThread = new Thread(new DownloadVerseThread()); 
    downloadThread.start(); 
    setContentView(R.layout.main); 
    TextView verseView = (TextView) findViewById(R.id.displayFighterVerse); 
    TextView dateView = (TextView) findViewById(R.id.displayDateRange); 
    TextView referenceView = (TextView) findViewById(R.id.displayReference); 
    try { 
     downloadThread.join(); 
    } catch (InterruptedException e) { 
     Log.e(TAG, "Attempted to set the UI values before we were ready."); 
     return; 
    } 
    Log.d(TAG, "Date: " + date); 
    Log.d(TAG, "Reference: " + reference); 
    Log.d(TAG, "Scripture: " + scripture); 
    progressDialog.dismiss(); 
    dateView.setText(date); 
    referenceView.setText(reference); 
    verseView.setText(scripture); 
} 



private class DownloadVerseThread implements Runnable { 


    @Override 
    public void run() { 

     try { 
      FighterVerseDownloader downloader = new FighterVerseDownloader(); 
      date = downloader.getDateRange(); 
      reference = downloader.getReference(); 
      scripture = downloader.getScripture(); 
     } catch (FighterVersesException e) { 
      Log.e("FighterVerses", "Failed to get the Fighter Verse", e); 
     }   
    } 

} 

的FighterVersesDownloader的構造是哪裏所有關於HTTP和DOM的工作都已完成。

關於我失蹤的任何想法？我在使用AsyncTask時看到了一些類似的線程，但我想直接使用優秀的老式線程，並且建議的解決方案不適用。

Answer 1

我認爲這個問題可能與你如何進行線程有關。當你調用downloadThread.join（）時，你基本上會花費那些代價昂貴的代碼，並將它放在方法的中間，阻塞進程中的UI線程。

當線程完成時，您需要使用回調方法來處理UI更改。你的代碼應該是這個樣子：

@Override 
public void onCreate(Bundle savedInstanceState) { 
    super.onCreate(savedInstanceState); 
    progressDialog = ProgressDialog.show(this, "", "Loading...", true); 
    Thread downloadThread = new Thread(new DownloadVerseThread()); 
    Handler downloadHandler = new Handler(); 
    Runnable downloadCallback = new Runnable(){ 
     public void run(){ 
       setContentView(R.layout.main); 
      TextView verseView = (TextView) findViewById(R.id.displayFighterVerse); 
      TextView dateView = (TextView) findViewById(R.id.displayDateRange); 
      TextView referenceView = (TextView) findViewById(R.id.displayReference); 
      Log.d(TAG, "Date: " + date); 
      Log.d(TAG, "Reference: " + reference); 
      Log.d(TAG, "Scripture: " + scripture); 
      progressDialog.dismiss(); 
      dateView.setText(date); 
      referenceView.setText(reference); 
      verseView.setText(scripture); 
     } 
    }; 
    downloadThread.start(); 
} 

private class DownloadVerseThread implements Runnable { 
    @Override 
    public void run() { 

     try { 
      FighterVerseDownloader downloader = new FighterVerseDownloader(); 
      date = downloader.getDateRange(); 
      reference = downloader.getReference(); 
      scripture = downloader.getScripture(); 
      downloadHandler.post(downloadCallback); 
     } catch (FighterVersesException e) { 
      Log.e("FighterVerses", "Failed to get the Fighter Verse", e); 
     }   
    } 
} 

這將保持在下載後臺線程，直到它完成，而不是幾乎立即分流它放回UI線程，因爲它是以前。編輯：Here's where I learned this。

Answer 2

我會推薦使用AsyncTask這種事情。