Android Java AsyncTask在外部工作

Question

I'm new in Java/Android and I come from c#. I've been taking a look into it and testing I found that when I execute an AsyncTask the mainthread keeps executing while the external task is doing it's work. I even found that I can only set the asynctask that execute an external task from the MainActivity.

My problem is that I want to execute an external class that when finished brings back the results(just like c#) to the maintask without setting the async class in the MainActivity.

So.. in code should be something like:

MainActivity.java

public onClickButton(View view) {
    String result = SecondaryClass.DoAsyncTask();
}

SecondaryClass.java

private class DoAsyncTask extends AsyncTask<Long, Integer, Integer> 
{
    @Override
    protected Integer doInBackground(Long... params) {
        String longString = ThirdAPIClass.GiveMeSomeCode(); //Or work here
        return lognString;
    }

    @Override
    protected void onPostExecute(String result) {
        return result; //Somehow(?)
    }
}

Any idea if there is something similar in Java/Android(?)

PD: I use AsyncTask as an example, I don't know if there is another instruction that do the same or something like that.

Answer 1

Class Singnature:

First Note is that if your result is a String then you need to change your extend clause to:

class DoAsyncTask extends AsyncTask<Long, Integer, String>

Communicating with calling activity:

The AsyncTask 's onPostExecute signature is void and it doesn't return data. The most common practices are:

1. To have this class as an inner class inside your activity, and onPostExecute you can call a method inside that activity.

2. Add a constuctor to you asyncTask class and pass the activity to it and then call the method using that instance of activity.

First Approach:

@Override
protected void onPostExecute(String result) {
        someMethodInMainActivity(result);
    }

Second Approach:

public class DoAsyncTask extends AsyncTask<Long, Integer, String> 
{
     YouActivityName  _activity;
     public DoAsyncTask(YouActivityName activity)
     {
        _activity = activity;
     }

     @Override
     protected String doInBackground(Long... params) {
        String longString = ThirdAPIClass.GiveMeSomeCode(); //Or work here
        return lognString;
     }

     @Override
     protected void onPostExecute(String result) {

        if(_activity != null) {
          _activity.someMethodInMainActivity(result);
        }
     }
}

Then you create your AsynTask using :

new DoAsyncTask(this);