AsyncTask 在后台运行时看不到 ProgressDialog [英] Can't see ProgressDialog while AsyncTask run in background

问题描述

我在我的应用程序中使用 AsyncTask 来下载一个 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，我看到了一会儿.想在下载时看到它而不是在那之后.谁能帮我.谢谢我的代码是这样的:

I use AsyncTask in my App for download a url. I use a ProgressDialog on onPreExecute() for waiting. But I cant see ProgressDialog while process finish and i see it for a moment. want to see it while downloading not after that. can any one help me. thanks my code is like this:

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();
    }
}

推荐答案

首先注意@override"标题附加到所有 AsyncTask 实现的方法，例如

Firstly notice the "@override" header attached to all the AsyncTask Implemented methods e.g.

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();

    }

}

同时从 doInBackground 中删除它，除非你必须在 UI 上做一些事情.

Also Remove this from doInBackground unless you must do something on the UI.

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

       // do something for downloading

    }
    });

您无法在 runOnUiThread 上执行下载操作.doInBackground 用于运行 UI 不可见的后台任务，如下载等.

You cannot do something for downloading on the runOnUiThread. doInBackground is meant for running background tasks like downloads etc. not visible to the UI.

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