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;
   }
}

我有这个代码会抛出错误。我需要一个显示直到成功的pbar = 0以外的东西。

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

这是我正在获取的logcat。我知道这是一件非常简单的事情，但它正在逃避我。任何建议将被认真考虑。 THX

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，但你永远不会看到对话框。

Answer 1

在AsyncTask中，您应该在onPreExecute / onPostExecute中设置您的UI活动，包括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;
       }
    }

Answer 2

您遇到的问题是因为您执行的线程几乎没有机会启动它完成。在它死后你和你的助手一起下载。您需要将下载代码移动到AsyncTask的doInBackground方法中。

这更符合必要：

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]);
    }
}

有关详细信息，请查看AsyncTask developer docs

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2 个答案: