Using a different class in Android Studio

Question

HOw do you use a method in a different class from the one you're calling it from in Android Studio? I have the following main class:

package com.example.bluebus;


import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.widget.TextView;

import java.util.concurrent.Executors;
import java.util.concurrent.ScheduledExecutorService;
import java.util.concurrent.ScheduledFuture;

import static java.util.concurrent.TimeUnit.SECONDS;

public class MainActivity extends AppCompatActivity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        BeeperControl test = new BeeperControl();
        //test.test();
        //test.test();*/

    }
}

and in the same folder I have the following BeeperControl class:

import java.util.concurrent.ScheduledFuture;

import static java.util.concurrent.TimeUnit.SECONDS;

/**
 * Created by Arthur on 1/7/2017.
 */

public class BeeperControl extends AppCompatActivity {
        /*private final ScheduledExecutorService scheduler =
                Executors.newScheduledThreadPool(1);*/
        final TextView text = (TextView) findViewById(R.id.text);
    /*
        public void beepForAnHour() {
            final Runnable beeper = new Runnable() {
                public void run() {
                    text.setText("Hello!");
                }
            };
            final ScheduledFuture<?> beeperHandle =
                    scheduler.scheduleAtFixedRate(beeper, 0, 1, SECONDS);
            scheduler.schedule(new Runnable() {
                public void run() { beeperHandle.cancel(true); }
            }, 60 * 60, SECONDS);
        }*/
        public void test(){
            text.setText("Who are you?");
        }
}

When written as is, the app works fine. However, when I uncomment test.test(), the app keeps closing when I try to run it in an emulator. From what I've seen, it may be a problem with updating the manifest, but I'm not sure how to fix it. Any help will be appreciated!

What are you trying to achieve by this? and why are you calling `findViewById(R.id.text);` outside `onCreate` of `BeeperControl`?!! (this will give you a `NullPointerExeption` BTW) — Atef Hares, Mar 30 '17 at 00:22
Bottom line, you never use `new` to instantiate an Activity. You'll need to use a LocalBroadcast, EventBus, or something similar. Take a look at both of the linked duplicates. — Daniel Nugent, Mar 30 '17 at 00:57

Prescott Chartier · Answer 1 · 2017-03-30T00:43:00.660

Have the method in the class return the value, your findbyid will return null as it is out of scope.

For example:

import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.widget.TextView;

import java.util.concurrent.Executors;
import java.util.concurrent.ScheduledExecutorService;
import java.util.concurrent.ScheduledFuture;

import static java.util.concurrent.TimeUnit.SECONDS;

public class MainActivity extends AppCompatActivity {

     @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        BeeperControl test = new BeeperControl();
        TextView text = (TextView) findViewById(R.id.text);
        text.setText(test.test());
        //test.test();*/

    }
}

Your Class:

import java.util.concurrent.ScheduledFuture;

import static java.util.concurrent.TimeUnit.SECONDS;

/**
 * Created by Arthur on 1/7/2017.
 */

public class BeeperControl extends AppCompatActivity {
        /*private final ScheduledExecutorService scheduler =
                Executors.newScheduledThreadPool(1);*/
        /* final TextView text = (TextView) findViewById(R.id.text);^/
    /*
        public void beepForAnHour() {
            final Runnable beeper = new Runnable() {
                public void run() {
                    text.setText("Hello!");
                }
            };
            final ScheduledFuture<?> beeperHandle =
                    scheduler.scheduleAtFixedRate(beeper, 0, 1, SECONDS);
            scheduler.schedule(new Runnable() {
                public void run() { beeperHandle.cancel(true); }
            }, 60 * 60, SECONDS);
        }*/
        public string test(){
            return ("Who are you?");
        }
}

This probably doesn't assist in your use of the class in whatever context it is used, if you pass text by reference to test() that may do it for you. R/ Prescott ...

I think that isn't actually the error. Yes, the object is final but OP is using methods to change the text which doesn't change the final object. — Kurt Acosta, Mar 30 '17 at 00:31
You would be correct, I revised my answer. As @ Atef Hares points out, the findbyid returns a null pointer. — Prescott Chartier, Mar 30 '17 at 00:35
Yes, it would invoke a NullPointerException because BeeperControl has no layout wherein in MainActivity, the layout is specified through the setContentView() method. But there's still something wrong in your code. Change line of `text = test.test()` to `text.setText(test.test())`. The text variable is a TextView and the test() method returns a String. The types are completely different and would cause another exception. :) — Kurt Acosta, Mar 30 '17 at 00:40
I constantly switch between VB.NET and C# with Android, iOS and Windows ... it's not pretty sometimes :), constant facepalming Thanks for the assistance. — Prescott Chartier, Mar 30 '17 at 00:53
Yes. I've recognized the code syntax and it looked like VB.NET. Anyway, it's an honest mistake. No worries and glad I could be of some help. :) — Kurt Acosta, Mar 30 '17 at 00:54

Using a different class in Android Studio

1 Answers1