Error "android (name of project) has stopped unexpectedly

package com.iperetz1.android.testbutton1;
import android.app.Activity;
import android.os.Bundle;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;

public class TestButton extends Activity {
    /** Called when the activity is first created. */
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);

        Button test2 = (Button)findViewById(R.id.test2);      
        test2.setOnClickListener(new OnClickListener()
        {
           @Override
           public void onClick(View v) 
           {
               setContentView(R.layout.test2);;
           }
        });

        Button other = (Button)findViewById(R.id.backmain);      
        other.setOnClickListener(new OnClickListener()
        {
           @Override
           public void onClick(View v) 
           {
               setContentView(R.layout.main);;
           }
        });
    }
}

main.xls

<?xml version="1.0" encoding="utf-8"?>
<AbsoluteLayout
android:id="@+id/widget0"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
xmlns:android="http://schemas.android.com/apk/res/android"
>
<Button
android:id="@+id/test2"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="test2"
android:layout_x="24px"
android:layout_y="165px"
>
</Button>
</AbsoluteLayout>

test2.xml

<?xml version="1.0" encoding="utf-8"?>
<AbsoluteLayout
android:id="@+id/widget0"
android:layout_width="fill_parent"
android:layout_height="fill_pare开发者_如何转开发nt"
xmlns:android="http://schemas.android.com/apk/res/android"
>
<Button
android:id="@+id/backmain"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="backmain"
android:layout_x="24px"
android:layout_y="165px"
>
</Button>
</AbsoluteLayout>

findViewById is a lot simpler than people tend to think it is. It traverses the view hierarchy looking for a view with the given ID. If it's not found, findViewById returns null.

You started by setting the content view to your main layout but later on you tried to findViewById(R.id.backmain). Since there is no view with that ID in your main layout, it returns null. At that point attempting other.setOnClickListener will fail. You will only be able to do this when your button actually exists in the view hierarchy.

There's nothing inherently wrong with dynamically changing your view hierarchy, but you'll have to handle some things differently if you go that route. (Such as when you wire up events to views that don't exist during onCreate like you're trying to do above.)

As @Cristian Castiblanco said, changing the view dynamically is causing the problem, for these kind of scenarios, you have to create separate activities and invoke them using intents and pass data between them using bundles.