ImageView通过相对路径引用Res/drawable下图片

package com.example.fragmenttest01;

import android.os.Bundle;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;
import android.widget.ImageView;
import android.app.Activity;
import android.content.pm.ApplicationInfo;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;

public class GetResImageActivity extends Activity {
    Button button;//获取图片资源btn
    ImageView imageview;
    
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_get_res_image);
        button = (Button) findViewById(R.id.button);
        imageview = (ImageView) findViewById(R.id.imageview);
            
        button.setOnClickListener(new OnClickListener(){
            @Override
            public void onClick(View arg0) {
                imageview.setImageBitmap(getRes("ic_launcher"));
            }
        });
    }
    
    //获取Res下的drawable文件夹下图片资源
    private Bitmap getRes(String imageName) {
        ApplicationInfo  appInfo = this.getApplicationInfo();
        int resID = getResources().getIdentifier(imageName, "drawable", appInfo.packageName);
        return BitmapFactory.decodeResource(getResources(), resID);
    }

}

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".GetResImageActivity" >

    <ImageView
        android:id="@+id/imageview"
        android:background="#99CC99"
        android:layout_width="150dp"
        android:layout_height="150dp"/>

    <Button
        android:id="@+id/button"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_alignParentRight="true"
        android:layout_alignParentTop="true"
        android:text="获取Res下图片" />
    
</RelativeLayout>