Gallery画廊使用 androidgalleryTypedArrayImageView

刚开始学习，懵懂的，遇到就网上找答案。
就说Gallery：
1。建立项目，把用到的图片存放到res/drawable目录。
2。res/layout/Activity_main.xml文件的内容如下：

<?xml version="1.0" encoding="utf-8"?>
<FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:id="@+id/FrameLayout01"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent" >

    <ImageView
        android:id="@+id/ImageView01"
        android:layout_width="fill_parent"
        android:layout_height="fill_parent"
        android:src="@drawable/aa" >
    </ImageView>

    <Gallery
        xmlns:android="http://schemas.android.com/apk/res/android"
        android:id="@+id/Gallery01"
        android:layout_width="fill_parent"
        android:layout_height="wrap_content"
        android:spacing="5dp" >
    </Gallery>

</FrameLayout>
3.在res/values/目录中新建一个attrs.xml内容如下：
<?xml version="1.0" encoding="UTF-8"?>
<resources>

    <declare-styleable name="HelloGallery">
        <attr name="android:galleryItemBackground"></attr>
    </declare-styleable>

</resources>
4.主类如下：
package com.example.gallery;

import android.app.Activity;
import android.content.Context;
import android.content.res.TypedArray;
import android.os.Bundle;
import android.view.Menu;
import android.view.View;
import android.view.ViewGroup;
import android.widget.AdapterView;
import android.widget.AdapterView.OnItemClickListener;
import android.widget.BaseAdapter;
import android.widget.Gallery;
import android.widget.ImageView;
import android.widget.Toast;

public class MainActivity extends Activity {

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
       
        final ImageView iv= (ImageView)findViewById(R.id.ImageView01);
        Gallery g = (Gallery) findViewById(R.id.Gallery01);

        //设置图片匹配器
        g.setAdapter(new ImageAdapter(this));

        //设置AdapterView点击监听器，Gallery是AdapterView的子类
        g.setOnItemClickListener(new OnItemClickListener() {

                @Override
                public void onItemClick(AdapterView<?> parent, View view,
                                int position, long id) {
                        //显示点击的是第几张图片
                        Toast.makeText(getApplicationContext(), "" + position,
                                        Toast.LENGTH_LONG).show();
                        //设置背景部分的ImageView显示当前Item的图片
                        iv.setImageResource(((ImageView)view).getId());
                }
        });
}

//定义继承BaseAdapter的匹配器
public class ImageAdapter extends BaseAdapter {

        //Item的修饰背景
        int mGalleryItemBackground;

        //上下文对象
        private Context mContext;

        //图片数组
        private Integer[] mImageIds = { R.drawable.b,
                        R.drawable.c, R.drawable.d,
                        R.drawable.e, R.drawable.g,
                        R.drawable.h, R.drawable.m,
                        R.drawable.l, R.drawable.k,
                        R.drawable.i };

        //构造方法
       
        public ImageAdapter(Context c){
                mContext = c;
                //读取styleable资源
//              TypedArray自定义标签的使用；获得自定义属性，存放在a中。 
        TypedArray a = mContext.obtainStyledAttributes(R.styleable.HelloGallery);
//        获取自定义属性id，后面使用自定义属性，通过id指定
        mGalleryItemBackground = a.getResourceId(
                R.styleable.HelloGallery_android_galleryItemBackground, 0);
        a.recycle();

        }

        //返回项目数量
        @Override
        public int getCount() {
                return mImageIds.length;
        }

        //返回项目
        @Override
        public Object getItem(int position) {
                return position;
        }

        //返回项目Id
        @Override
        public long getItemId(int position) {
                return position;
        }

        //返回视图
        @Override
        public View getView(int position, View convertView, ViewGroup parent) {

                ImageView iv = new ImageView(mContext);
//                为画廊中每个画框添加图片
                iv.setImageResource(mImageIds[position]);
                //给生成的ImageView设置Id，不设置的话Id都是-1
                iv.setId(mImageIds[position]);
                iv.setLayoutParams(new Gallery.LayoutParams(120, 160));
//                控制为了使图片适合 ImageView 的大小，FIT_XY为拉伸
                iv.setScaleType(ImageView.ScaleType.FIT_XY);
//                为画廊添加主题风格。通过id指定
                iv.setBackgroundResource(mGalleryItemBackground);
                return iv;
        }


    }

    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        getMenuInflater().inflate(R.menu.activity_main, menu);
        return true;
    }
}