Button不是放在RelativeLayout中的

xml:

<?xml version="1.0" encoding="utf-8"?>
<Button xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:id="@+id/myButton"
    android:text="My Button" />

package com.example.androidtest;

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


public class MainActivity extends Activity {
	
	public void onCreate(Bundle savedInstanceState)
	{
		super.onCreate(savedInstanceState);
		setContentView(R.layout.activity_main);
		
		Button myButton = (Button)findViewById(R.id.myButton);
		myButton.setOnClickListener(clickListener);
	}
	
	View.OnClickListener clickListener = new View.OnClickListener() {
		
		@Override
		public void onClick(View v) {
			// TODO Auto-generated method stub
			
		}
	};
	
}