Question

我正在编写一个Activity，它通过HTTP从Web中获取一些XML，然后将其解析为DOM。然后它从DOM中提取一些所需的数据。

您可以想象，这需要一些时间，因此我将该代码放入其自己的线程中，然后尝试设置ProgressDialog以在用户等待完成时显示。

问题是ProgressDialog根本不显示。如果我删除了对dismiss（）的调用，那么它会在工作完成后显示，显然，只是坐在那里......

这是我的代码：

@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);
        }           
    }

}

FighterVersesDownloader的构造函数是完成HTTP和DOM方面的所有工作的地方。

关于我缺少的任何想法？我已经在使用AsyncTask看到了一些相似的线程，但是我想直接使用好的老式Threads并且建议的解决方案不适用。

Answer 1

我建议使用AsyncTask来处理这类事情。

Answer 2

我认为问题可能与你如何进行线程有关。当你调用downloadThread.join（）时，你基本上就是拿着那些昂贵的代码并在方法中间把它打好，在这个过程中阻塞了UI线程。

当线程完成时，您需要使用回调方法来处理UI更改。您的代码应如下所示：

@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);
        }           
    }
}

这会将后续线程中的下载保留到完成之前，而不是像以前那样立即将其分流回UI线程。

编辑：Here's where I learned this。

ProgressDialog不会出现，直到为时已晚

2 个答案: