android asynktask取消不起作用

Question

I'm trying to create a login in my app.

This is my Login activity, where I've created an Asynktask where I'm looking to cancel if the result of getUser() is null.

public class Login extends AsyncTask<String, Void, Void> {

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

        @Override
        protected Void doInBackground(String... params) {
            ArrayList<String> userValues = new ArrayList<String>();

userValues.add(((EditText)findViewById(R.id.usermail)).getText().toString());

            userValues.add("john");

            if((response = new Database().getUser(userValues)) == "null") {
                cancel(true);
            }

            return null;
        }

        @Override
        protected void onCancelled() {
            Toast.makeText(getApplicationContext(), "Not registered", Toast.LENGTH_SHORT).show();
        }

        @Override
        protected void onPostExecute(Void result) {
            Toast.makeText(getApplicationContext(), response, Toast.LENGTH_SHORT).show();
            super.onPostExecute(result);
        }
    }
}

I wish to cancel the procedure of "login" if the returned value on Database.getUser() returns "null". But it seems that is not working and I don't know if I'm either doing something wrong or I'm forgetting something.

Thank you very much in advance.

Answer 1

cancel(allowInterrupt)

Calling this method will result in onCancelled(Object) being invoked on the UI thread after doInBackground(Object[]) returns. Calling this method guarantees that onPostExecute(Object) is never invoked.

That being said, use can use the following approach:

public class Login extends AsyncTask<String, Boolean, Boolean> {

    @Override
    protected Boolean doInBackground(String... params) {
        if (getUser() == null){
             // exit from this doInBackground and proceed to postExecute
             return false;
        }

        // continue

        return true;
    }

    @Override
    protected void onPostExecute(Boolean result) {
        if (result){
           // succes
        }else {
           // cancelled
        }
    }
}

}

Answer 2

Attempts to cancel execution of this task. This attempt will fail if the task has already completed, already been cancelled, or could not be cancelled for some other reason. in my view you can handle the login process on onpost execute as per the result set flag that user can login or not