AsyncTask在后台运行时看不到ProgressDialog

Question

我在应用程序中使用AsyncTask下载URL。我在onPreExecute（）上使用ProgressDialog进行等待。但是我在进程完成时看不到ProgressDialog，我看了一会儿。想要在下载之后看到它。谁能帮我。谢谢我的代码是这样的：

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

    @Override
    protected void onPreExecute() {
        // Showing progress dialog before sending http request
        pDialog = new ProgressDialog(SingleMenuItemActivity.this);
        pDialog.setMessage("Please Wait ...");
        pDialog.isIndeterminate();
        pDialog.setCancelable(false);
        pDialog.show();
    }

    protected Void doInBackground(Void... unused) {
        runOnUiThread(new Runnable() {
            public void run() {

           // do something for downloading

        }
        });

        return (null);
    }


    protected void onPostExecute(Void unused) {
        // closing progress dialog
        pDialog.dismiss();
    }
}

Answer 1

首先，请注意所有AsyncTask实现的方法附带的“ @override”标头，例如

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

    ProgressDialog pDialog;

    @Override
    protected void onPreExecute() {
        // TODO Auto-generated method stub
        super.onPreExecute();
        pDialog = new ProgressDialog(SingleMenuItemActivity.this);
        pDialog.setMessage("Please Wait ...");
        pDialog.isIndeterminate();
        pDialog.setCancelable(false);
        pDialog.show();
    }

    @Override
    protected Void doInBackground(Void... params) {
        // TODO Auto-generated method stub

        return null;
    }

    @Override
    protected void onPostExecute(Void result) {
        // TODO Auto-generated method stub
        super.onPostExecute(result);
        pDialog.cancel();

    }

}

除非您必须在UI上执行某些操作，否则还要从doInBackground中删除它。

runOnUiThread(new Runnable() {
        public void run() {

       // do something for downloading

    }
    });

您无法在runOnUiThread上进行任何下载操作。doInBackground用于运行后台任务，例如对UI不可见的下载等。