android 入门 imageView

package com.zte.android.lession;

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

public class Activity_imageview_006 extends Activity
{
	private ImageView imageView ;
	private Button changeBtn,alphaBtn ;
	
	@Override
	protected void onCreate(Bundle savedInstanceState) {
		// TODO Auto-generated method stub
		super.onCreate(savedInstanceState);
		
		setContentView(R.layout.imageview_layout_006);
		//实例化组件
		imageView = (ImageView)findViewById(R.id.l006_imageView1);
		changeBtn = (Button)findViewById(R.id.l006_button1);
		alphaBtn = (Button)findViewById(R.id.l006_button2);
		
		//set listener
		changeBtn.setOnClickListener(new OnClickListener() {
			@Override
			public void onClick(View v) {
				// TODO Auto-generated method stub
				imageView.setImageResource(R.drawable.girl_c);
			}
		});
		alphaBtn.setOnClickListener(new OnClickListener() {
			@Override
			public void onClick(View v) {
				// TODO Auto-generated method stub
				imageView.setAlpha(80);
			}
		});
	}
}

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical" >

    <ImageView
        android:id="@+id/l006_imageView1"
        android:layout_width="wrap_content"
        android:layout_height="100dp"
        android:src="@drawable/car_b" />

    <Button
        android:id="@+id/l006_button1"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="换图" />

    <Button
        android:id="@+id/l006_button2"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="透明度" />

</LinearLayout>