Cannot pass values to an AsyncTask in Android

Issue

I am using an AsyncTask in an activity.

here is my code

public class MyActivity extends AppCompatActivity {


 EditText editUserNameLogin;
 EditText editPassLogin;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.login);
    //ButterKnife.bind(this);

    editUserNameLogin = (EditText) findViewById(R.id.input_username_login);
    editPassLogin = (EditText) findViewById(R.id.input_password_login);

}

public class AsyncTaskClass extends AsyncTask<String, String, String> {


    String strUserName = editUserNameLogin.getText().toString();
    String passLogin = editPassLogin.getText().toString();


    @Override
    protected void onPreExecute() {

    }

    @Override
    protected String doInBackground(String... params) {

        Toast.makeText(MyActivity.this, passLogin, Toast.LENGTH_SHORT).show();
    }

    @Override
    protected void onPostExecute(String r) {

    }
}

but in doInBackground can't get values passLogin or strUserName (Toast.makeText(MyActivity.this, passLogin,) don't show any text)

Solution

You can not perform UI operation inside background AsyncTask doInBackground method because AsyncTask not work with current UI thread, its create new thread while you initialize and execute.

Let me explain you in bref.

While activity start its stay with Activity Thread and when you complete activity operation and destroy its completely remove from operation task. But while you start AsyncTask on Activity its start with individual operation stat that not depends on activity that you start, so if you perform UI operation in doInBackground method and in case Activity destroyed and you working on UI that already destroyed by activity and UI cannot get reference, its generate an exception. So it's necessary to work with current activity thread not another background thread.

There are many case that you can pass data inside AsyncTask, i'm comfortable with below operation, it can help you also.

// Pass data to AsyncTask comma separated values
new MyBackgroundTask().execute("Hello there!","How are you?");

private class MyBackgroundTask extends AsyncTask<String, Void, Void> {
    @Override
    protected void onPreExecute() {
        super.onPreExecute();
    }

    @Override
    protected Void doInBackground(String... strings) {
        String message1 = strings[0];
        String message2 = strings[1];

        Log.d("_TAG_", "First String: " + message1);
        Log.d("_TAG_", "Second String: " + message2);
        return null;
    }

    @Override
    protected void onPostExecute(Void aVoid) {
        super.onPostExecute(aVoid);
    }
}

For more information read Android Official Documents AsyncTask Developer Guides

Answered By - Rahul Mandaliya