Get AsyncTask's result without blocking the thread

Issue

I have the code that sends requests to REST API in AsyncTask. Also, I have a ProgressDialog initialization in preExecute() and its dismission in postExecute().

I want ProgressDialog to show an indeterminate spinner (you know, that loading animation), but I need to get a result too. get() blocks the main thread where I'm invoking it in - what's the workaround for that case?

Main thread (main activity)

LoginTask task_login = new LoginTask();
                AsyncTask<String, Void, JSONObject> response = task_login.execute(et_username.getText().toString(), et_password.getText().toString());
                try {
                    JSONObject json = response.get();
                    Toast.makeText(MainActivity.this, json.toString(), Toast.LENGTH_SHORT).show();
                } catch (InterruptedException e) {
                    Toast.makeText(MainActivity.this, "Interrupted.", Toast.LENGTH_SHORT).show();
                } catch (Exception e) {
                    e.printStackTrace();
                }

AsyncTask (dummy doInBackground):

public class LoginTask extends AsyncTask<String, Void, JSONObject> {
    private LoginTask self = this;
    private ProgressDialog progressDialog;

    @Override
    protected JSONObject doInBackground(String... params) {
        try {
            Thread.sleep(5000);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        return null;
    }

    @Override
    protected void onPreExecute() {
        super.onPreExecute();

        progressDialog = ProgressDialog.show(MainActivity.context,
                "Logging in...", "");
        progressDialog.setButton(DialogInterface.BUTTON_NEUTRAL,
                MainActivity.context.getResources().getResourceEntryName(R.string.dialog_button_cancel), new DialogInterface.OnClickListener() {
                    @Override
                    public void onClick(DialogInterface dialog, int which) {
                        dialog.cancel();
                    }
                });

        progressDialog.setCanceledOnTouchOutside(false);
        progressDialog.setOnCancelListener(new DialogInterface.OnCancelListener() {
            @Override
            public void onCancel(DialogInterface dialog) {
                self.cancel(true);
            }
        });
    }

    @Override
    protected void onPostExecute(JSONObject jsonObject) {
        super.onPostExecute(jsonObject);

        progressDialog.dismiss();
    }

}

Solution

Please look at the usage of AsyncTask https://developer.android.com/reference/android/os/AsyncTask#usage

There is a callback function onPostExecute which returns (as parameter) the value you requested:

private class RestTask extends AsyncTask<Object, Object, String> {
    protected String doInBackground(Object... args) {
        // this happend on background thread
        return downloadData();
    }

    protected void onPreExecute() {
        // this happend on UI thread
        showSpinner();
    }

    protected void onPostExecute(String result) {
        // this happend on UI thread
        hideSpinner();
        doSomethingWithDownloadResult(result);
    }
}

Usage:

new RestTask().execute()

---

As you edited the question, this:

try {
    JSONObject json = response.get();
    Toast.makeText(MainActivity.this, json.toString(), Toast.LENGTH_SHORT).show();
} catch (InterruptedException e) {
    Toast.makeText(MainActivity.this, "Interrupted.", Toast.LENGTH_SHORT).show();
} catch (Exception e) {
    e.printStackTrace();
}

should be called in previous Tasks onPostExecute method, this way you will not block you UI with get method waiting on login result.

Answered By - Gaskoin