如何在一个Activity中运行两个AsyncTasks? [英] How run two AsyncTasks in one Activity?

问题描述

我有两个Activity(mainActivity& downloadActivity)，而我在downloadActivity中有2个AsyncTask

I have two Activitys (mainActivity & downloadActivity) and I have 2 AsyncTasks in downloadActivity

在downloadActivity中，它首先执行getFileAsyncTask以读取JSON文件以添加一些图像并从图像中创建ListView，如果用户单击图像，则会调用downloadAsyncTask并开始下载内容来自网络. 我的问题在这里:当第二个AsyncTask运行时，我回到mainActivity并再次返回到downloadActivity，直到downloadAsyncTask完成时才调用第一个AsyncTask.

In downloadActivity first it execute getFileAsyncTask for reading a JSON file for adding some images and create a ListView from images, if user clicks on an image, the downloadAsyncTask was called and it starts to download something from the internet. My problem is here: when the second AsyncTask is running I go back to mainActivity and comeback again to downloadActivity the first AsyncTask wasn't called until the downloadAsyncTask completed.

public class downloadActivity extends ActionBarActivity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        ...
        new getFileAsyncTask().execute();
        ...
    }
    private class getFileAsyncTask extends AsyncTask<Void, Void, Void> {
        @Override
        protected Void doInBackground(Void... params) {
        //fetch a json file from internet and add images in ListView
            return null;
        }
    }
    //there is a Base Adapter class 
    //if user clicks on an image it calls this downloadAsyncTask.execute()
    private class downloadAsyncTask extends AsyncTask<Void, Integer, Void> {
        @Override
        protected void onPreExecute() {
        //download the file
        }
    }

    @Override
    protected Void doInBackground(Void... unused) {
        //download the file
    }
}

注意:我想编写类似购物应用程序的内容.例如，用户可以下载文件并浏览商店以查看产品.

note: I want to write something like shopping apps. For example, user can download file and surf into shop to see products .

推荐答案

如果要并行运行多个AsyncTasks，则可以在任务上调用executeOnExecutor(AsyncTask.THREAD_POOL_EXECUTOR)而不是execute().默认情况下，AsyncTasks以串行方式运行，先到先得.

If you want to run multiple AsyncTasks in parallel, you can call executeOnExecutor(AsyncTask.THREAD_POOL_EXECUTOR) instead of execute() on your task. By default, AsyncTasks run in serial, first come first serve.

请注意，两个线程不会在同一数据上交互，这可能会导致一些奇怪且难以跟踪的错误.

Be careful that the two threads do not interact on the same data, this can cause some strange and hard to trace errors.

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