How to Properly Return a Boolean Value from an Android AsyncTask?

How to Return a Boolean Value from AsyncTask

In Android programming, AsyncTask is a class designed to perform background operations in a separate thread. In this context, the challenge arises when you need to return a boolean value from an Async task, as it operates asynchronously.

Consider the scenario where you have a user interface with EditTexts for FTP address, username, password, and port. When the user clicks the "testConnection" button, a connection is attempted, and a boolean value is returned based on the connection status.

Challenge in Returning Boolean from Async Task

Initially, the code may look similar to the provided example:

boolean status = ftpConnect(_address, _username, _password,_port);
ftpDisconnect();

if (status == true) {
 Toast.makeText(SiteManager.this, "Connection Succesful",
 Toast.LENGTH_LONG).show();
 } else {
 Toast.makeText(SiteManager.this,
 "Connection Failed:" + status, Toast.LENGTH_LONG).show();

 } 

However, when using AsyncTask, the code within doInBackground will run in the background, and the onPostExecute method will be called regardless of the result of the background operation. This means that the boolean status will not be available in the onPostExecute method.

Solution: Implementing a Callback Interface

To overcome this challenge, we can implement a callback interface. Here's how:

public interface MyInterface {
    public void myMethod(boolean result);
}

public class AsyncConnectTask extends AsyncTask<Void, Void, Boolean> {

    private MyInterface mListener;


    public AsyncConnectTask(Context context, String address, String user,
        String pass, int port, MyInterface mListener) {
        mContext = context;
        _address = address;
        _user = user;
        _pass = pass;
        _port = port;
        this.mListener  = mListener;
    }

    @Override
    protected Boolean doInBackground(Void... params) {
        ....
        return result;
   }


    @Override
    protected void onPostExecute(Boolean result) {
        if (mListener != null) 
            mListener.myMethod(result);
    }
}

Now, in your activity or fragment:

AsyncConnectTask task = new AsyncConnectTask(SiteManager.this,
                        _address, _username, _password, _port,  new MyInterface() {
    @Override
    public void myMethod(boolean result) {
        if (result == true) {
            Toast.makeText(SiteManager.this, "Connection Succesful",
            Toast.LENGTH_LONG).show();
        } else {
            Toast.makeText(SiteManager.this, "Connection Failed:" + status, Toast.LENGTH_LONG).show();
        } 
    }
});

task.execute();

This approach ensures that the result from doInBackground is passed back to the UI thread through the callback interface. You can call myMethod from onPostExecute to execute the code on the UI Thread otherwise, you'll need to post a Runnable through a Handler.

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