如何制作一个“哑”的进度条？

Question

private void Load()
{
    new pbar().execute();
    //dialog = ProgressDialog.show(Display.this, "", "Loading. Please wait...", true);
    success = faHelper.SourceDownload(Url);
    displaystuff();
    //dialog.dismiss();
}

private class pbar extends AsyncTask<Void, Void, Void> 
{
   protected Void doInBackground(Void...unused) 
   {
       dialog = ProgressDialog.show(Display.this, "", "Loading. Please wait...", true);
       while (success == 0) {}
       dialog.dismiss();
       return null;
   }
}

我有这个引发错误的代码。我需要一个显示直到成功的 pbar = 0 以外的值。

10-06 16:34:52.802: ERROR/AndroidRuntime(6055): FATAL EXCEPTION: AsyncTask #1
10-06 16:34:52.802: ERROR/AndroidRuntime(6055): java.lang.RuntimeException: An error occured while executing doInBackground()
10-06 16:34:52.802: ERROR/AndroidRuntime(6055):     at android.os.AsyncTask$3.done(AsyncTask.java:200)
10-06 16:34:52.802: ERROR/AndroidRuntime(6055):     at java.util.concurrent.FutureTask$Sync.innerSetException(FutureTask.java:274)
10-06 16:34:52.802: ERROR/AndroidRuntime(6055):     at java.util.concurrent.FutureTask.setException(FutureTask.java:125)
10-06 16:34:52.802: ERROR/AndroidRuntime(6055):     at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:308)
10-06 16:34:52.802: ERROR/AndroidRuntime(6055):     at java.util.concurrent.FutureTask.run(FutureTask.java:138)
10-06 16:34:52.802: ERROR/AndroidRuntime(6055):     at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1088)
10-06 16:34:52.802: ERROR/AndroidRuntime(6055):     at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:581)
10-06 16:34:52.802: ERROR/AndroidRuntime(6055):     at java.lang.Thread.run(Thread.java:1027)
10-06 16:34:52.802: ERROR/AndroidRuntime(6055): Caused by: java.lang.RuntimeException: Can't create handler inside thread that has not called Looper.prepare()
10-06 16:34:52.802: ERROR/AndroidRuntime(6055):     at android.os.Handler.<init>(Handler.java:121)
10-06 16:34:52.802: ERROR/AndroidRuntime(6055):     at android.app.Dialog.<init>(Dialog.java:145)
10-06 16:34:52.802: ERROR/AndroidRuntime(6055):     at android.app.AlertDialog.<init>(AlertDialog.java:63)
10-06 16:34:52.802: ERROR/AndroidRuntime(6055):     at android.app.ProgressDialog.<init>(ProgressDialog.java:80)
10-06 16:34:52.802: ERROR/AndroidRuntime(6055):     at android.app.ProgressDialog.<init>(ProgressDialog.java:76)
10-06 16:34:52.802: ERROR/AndroidRuntime(6055):     at android.app.ProgressDialog.show(ProgressDialog.java:101)
10-06 16:34:52.802: ERROR/AndroidRuntime(6055):     at android.app.ProgressDialog.show(ProgressDialog.java:90)
10-06 16:34:52.802: ERROR/AndroidRuntime(6055):     at com.Testapp3.Display$pbar.doInBackground(Display.java:132)
10-06 16:34:52.802: ERROR/AndroidRuntime(6055):     at com.Testapp3.Display$pbar.doInBackground(Display.java:1)
10-06 16:34:52.802: ERROR/AndroidRuntime(6055):     at android.os.AsyncTask$2.call(AsyncTask.java:185)
10-06 16:34:52.802: ERROR/AndroidRuntime(6055):     at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:306)
10-06 16:34:52.802: ERROR/AndroidRuntime(6055):     ... 4 more

这就是我得到的 logcat。我知道这是非常简单的事情，但它正在逃避我。任何建议将被认真考虑。谢谢

更新代码：

private void Load()
{
    new pbar().execute();
    success = faHelper.SourceDownload(Url);
    displaystuff();
}

private class pbar extends AsyncTask<Void, Void, Void> 
{

    @Override
    protected void onPreExecute() 
    {
        dialog = ProgressDialog.show(Display.this, "", "Loading. Please wait...", true);
    }

    @Override
    protected void onPostExecute(Void result) 
    {
        dialog.dismiss();
        return;
    }

    protected Void doInBackground(Void...unused) 
    {
        while (success == 0) {}
        return null;
    }
}

错误消失了，但你永远看不到对话框。

Answer 1

您遇到的问题是因为您正在执行的线程在完成之前几乎没有机会启动。然后在它死后你正在下载你的助手。您需要将下载代码移动到 AsyncTask 的 doInBackground 方法中。

这更像是必要的：

private void Load()
{
    new pbar().execute(url);
}

private class pbar extends AsyncTask<Url, Void, Long> 
{
    private final String message = "Loading. Please wait...";
    private int success=0;

    @Override
    protected void onPreExecute() 
    {
        dialog = ProgressDialog.show(Display.this, "", message, true);
    }

    @Override
    protected void onPostExecute(Long result) 
    {
        dialog.dismiss();
        Display.displaystuff();
    }

    protected Long doInBackground(Url... urls) 
    {
        return faHelper.SourceDownload(urls[0]);
    }
}

欲了解更多信息，请查看AsyncTask developer docs

Answer 2

在 AsyncTask 中，您应该设置 UI 活动，包括 onPreExecute/onPostExecute 中的 ProgressDialog，如下所示：

   private void Load()
   {
    new pbar().execute();

   }

   private class pbar extends AsyncTask<Void, Void, Void> 
    {

    @Override
    protected void onPreExecute() {
           dialog = ProgressDialog.show(Display.this, "", "Loading. Please wait...", true);
    }

    @Override
    protected void onPostExecute(Void result) {
              dialog.dismiss();
              displaystuff();
              return;
    }

       protected Void doInBackground(Void...unused) 
       {
           success = faHelper.SourceDownload(Url);
            return null;
       }
    }