In android eclipse, how can i run a second class to execute some commands?

Question

For instance, the mainActivity.java file is really clustered and to keep it clean i created a second .java(class) where i will execute some code upon a button press. I cannot figure out how to do it at all. And i am not sure what search terms to use either so i apologize if this has been covered.

Heres what i have in my "test" application.

I have a main activity with a single button on it.

package com.test.secondclass;

import android.os.Bundle;
import android.app.Activity;
import android.content.Intent;
import android.view.Menu;
import android.view.View;
import android.widget.Button;

public class MainActivity extends Activity {

    Button startButton;
    final Intent second = new Intent(getApplicationContext(), testClass.class);

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        startButton = (Button)findViewById(R.id.button1);

        startButton.setOnClickListener(new View.OnClickListener() {

            @Override
            public void onClick(View v) {
                // TODO Auto-generated method stub
                startActivity(second);

            }
        });
    }

    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        // Inflate the menu; this adds items to the action bar if it is present.
        getMenuInflater().inflate(R.menu.activity_main, menu);
        return true;
    }

}

Now here is the "second" class that i made, now remember this is very short i am just using this for an exercise program before implementing it into my actual program.

package com.test.secondclass;

import android.app.Activity;
import android.widget.Toast;

public class testClass extends Activity{

    public void onCreate(){
        Toast.makeText(getApplicationContext(), "Second class thinger started", Toast.LENGTH_LONG).show();
    }
}

And if i try this i get a force close immediately. If i comment out the "intent" part at the very beginning of my main activity then the program runs. But it doesnt do what i want. obviously. Thanks everyone

Answer 1

Add an OnClickListener to send whatever information to testClass, as shown below (untested):

button.setOnClickListener(new OnClickListener() {
    public void onClick(View v) {
        Intent secondIntent = new Intent();
        secondIntent.setClassName(myPackageName, "testClass");
        startActivityForResult(secondIntent, REQUEST_CODE);
});

References here and here.

Answer 2

Here's my viewpoint: you are receiving a forced close due the fact that you is trying to open user interface methods (such the Toast) with no context.

IMPORTANT: I'm assuming that you already defined both classes in the manifest.xml file!

Before explaining, I'll make a brief: Toast: this class opens a quick message, receiving as main arguments the context, the message and the time-to-show; The context: it is the "environment" where to show. Something like a visual scope, that defines the resources you have. In most cases, you can setup it with setContentView method.

Issue Explanation, in my opinion: The "crash" occurs because you opens the Toast message with no context. An activity is a UI control very similar to a viewpage. If you call a new activity, its very like to call a new page, and so, a new context. In the seccond activity, I haven't see any context. I think that you was assuming that the context is preserved from the first activity, but it ins't because its a new activity.

How to fix:

• In the seccond class, define a layout view with setContentView, or...
• Reimplement your seccond class as a Service, and call it through startService, or...
• Define an AIDL mechams (similar to previous fix, but more sophisticated and complex, as it enables async method calls).

Hope it has helped in some way.

Answer 3

Thank you ALL for the answers!! I was actually able to do what i wanted by using the "stopSelf()" command after i displayed the Toast message. I implemented a service class and when i press the button the testClass.java class gets called and runs the "toast" message then immediately exits by the "stopSelf()" command. I made sure of this by including an "onDestroy()" method which also displayed a simple toast message confirming that the service was stopping :). I usually do stuff like this using threads but it was making the main activity really messy no matter how much formatting i did. So i wanted to have a seperate class i could use.

And to the commenter EfEs, i come from programming in C# language for windows. Android is a new playground for me and im still learning. i think im doing quite well but wasnt sure how to do what i asked. But i figured it out then. And thanks for clearing up that an Activity in android is like a "WindowsForm" in C# where it is completely new GUI for the user. I didnt know that. But thanks to all for helping me with your posts!