Android 等待异步任务完成执行特定方法

Question

I have been searching for the answer but no one really answers because there is no point using async task for that. In Android API 11 or above it will force to code it you do network requests on the main thread so I have to do async task. So, here is the question: Is it possible to wait untill the async task is finished then continue? Because I need the data to be there for the calling method etc.

Here is my code:

public JSONObject getJSONFromUrl(String url) {
        this.url = url;
        new loadURL().execute();



        // Do this when ASYNC HAS FINISHED 
        return jObj;



    }

    class loadURL extends AsyncTask <Void, Void, Void> {

        protected void onPreExecute() {

        }

        protected Void doInBackground(Void... unused) {
            //do stuff in background 

            return (null);
        }

    }   
}

Any questions to answer just leave a comment. Thanks for helping.

Answer 1

yes you use the onPostExecute method of the AsyncTask to do whatever you want to do after. That method gets called after the doInBackground is finished

Answer 2

If the operation won't take long (less than a few seconds) you can use the progress bar to keep from allowing the user to do anything. Set something like this in your AsyncTask

ProgressDialog progress = ProgressDialog.show(LoginScreen.this, "Downloading Users", "Please wait while users are downloaded");

    @Override
    protected void onPreExecute()
    {
        progress.setCancelable(false);
        progress.isIndeterminate();
        progress.show();
    }

You will still want to call your method from onPostExecute() as this will just keep the user from being able to do anything but it won't keep any code from running that is in the method you calling the AsyncTask from

Answer 3

This can be done with wait() , notify() and notifyAll() methods of object s. Or You can use custom callbacks via interface s. Just call proper method via callback when you complete getting required data.

Answer 4

您可以在doInBackground()方法中执行网络相关操作，因为onPostExecute()方法仅用于 android 中的 UI 更新