Simple Button for Android – XML onClick + public method

Probably the simplest way to create Android Button. Create a new public method (e.g. goButtonClicked) and add it to your layout XML.
Prequisites: Android Hello World Explained
In Java, define a new public method that takes view as parameter.

public void goButtonClicked(View v) {
        // do stuff
}

In your XML file, create a new button. Name your method as onClick property for the button.

<Button android:text="Go!" android:onClick="goButtonClicked"
        android:id="@+id/goButton"></Button>

That’s it.
Below, a complete example code.

Complete Code Example for Simple Button

res/layout/main.xml

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
 android:orientation="vertical"
 android:layout_width="fill_parent"
 android:layout_height="fill_parent"
 >
<TextView  
 android:layout_width="fill_parent"
 android:layout_height="wrap_content"
 android:text="@string/hello"
 />
<Button android:layout_height="wrap_content"
 android:layout_width="wrap_content" android:text="Go!"
 android:onClick="goButtonClicked" android:id="@+id/goButton"></Button>
</LinearLayout>

SimplestButtonActivity.java

package com.botbook.simplestbutton;
import android.app.Activity;
import android.content.Context;
import android.os.Bundle;
import android.view.View;
import android.widget.Toast;
public class SimplestButtonActivity extends Activity {
    /** Called when the activity is first created. */
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);
    }
    public void goButtonClicked(View v) {
    	tToast("Go button clicked!");
    }
    private void tToast(String s) {
        Context context = getApplicationContext();
        int duration = Toast.LENGTH_LONG;
        Toast toast = Toast.makeText(context, s, duration);
        toast.show();
    }
}

See also:
Android Reference: Button