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自从Gallery被谷歌废弃以后，Google推荐使用ViewPager和HorizontalScrollView来实现Gallery的效果。的确HorizontalScrollView可以实现Gallery的效果，但是HorizontalScrollView存在一个很大的问题，如果你仅是用来展示少量的图片，应该是没问题的，但是如果我希望HorizontalScrollView可以想ViewPager一样，既可以绑定数据集（动态改变图片），还能做到，不管多少图片都不会OOM（ViewPager内部一直初始化，回收，至多只保持3个View）。本篇博客首先介绍HorizontalScrollView的简单用法，然后会在此基础上进行扩展，自定义HorizontalScrollView实现我们上面提到的效果，类似一屏可以显示多个View的ViewPager，再多的图片也不怕OOM。

1、HorizontalScrollView的简单用法

HorizontalScrollView其实是FrameLayout的子类，所以内部只能有一个直接的子View。我们用来做Gallery效果，首选当然是LinearLayout，然后方向设置为水平。
1、布局文件：

<LinearLayout 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"  
     >  
    <HorizontalScrollView  
        android:layout_width="wrap_content"  
        android:layout_height="150dp"  
        android:layout_gravity="center_vertical"  
        android:background="#AA444444"  
        android:scrollbars="none" >  
  
        <LinearLayout  
            android:id="@+id/id_gallery"  
            android:layout_width="wrap_content"  
            android:layout_height="wrap_content"  
            android:layout_gravity="center_vertical"  
            android:orientation="horizontal" >  
        </LinearLayout>  
    </HorizontalScrollView>  
  
</LinearLayout>  

很简单，就一个HorizontalScrollView内部有个水平方向的LinearLayout
MainActivity:

package com.example.zhy_horizontalscrollview;  
  
import android.app.Activity;  
import android.os.Bundle;  
import android.view.LayoutInflater;  
import android.view.View;  
import android.view.Window;  
import android.widget.ImageView;  
import android.widget.LinearLayout;  
import android.widget.TextView;  
  
public class MainActivity extends Activity  
{  
  
    private LinearLayout mGallery;  
    private int[] mImgIds;  
    private LayoutInflater mInflater;  
  
    @Override  
    protected void onCreate(Bundle savedInstanceState)  
    {  
        super.onCreate(savedInstanceState);  
        requestWindowFeature(Window.FEATURE_NO_TITLE);  
        setContentView(R.layout.activity_main);  
        mInflater = LayoutInflater.from(this);  
        initData();  
        initView();  
  
    }  
  
    private void initData()  
    {  
        mImgIds = new int[] { R.drawable.a, R.drawable.b, R.drawable.c,  
                R.drawable.d, R.drawable.e, R.drawable.f, R.drawable.g,  
                R.drawable.h, R.drawable.l };  
    }  
  
    private void initView()  
    {  
        mGallery = (LinearLayout) findViewById(R.id.id_gallery);  
  
        for (int i = 0; i < mImgIds.length; i++)  
        {  
              
            View view = mInflater.inflate(R.layout.activity_index_gallery_item,  
                    mGallery, false);  
            ImageView img = (ImageView) view  
                    .findViewById(R.id.id_index_gallery_item_image);  
            img.setImageResource(mImgIds[i]);  
            TextView txt = (TextView) view  
                    .findViewById(R.id.id_index_gallery_item_text);  
            txt.setText("some info ");  
            mGallery.addView(view);  
        }  
    }  
  
}  

很简单，我预先准备了一些图片直接放在了Drawble下，然后循环加入HorizontalScrollView的LinearLayout中即可，Item的布局就省了，后面会贴源码。
效果图：

<LinearLayout 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"  
    android:background="@android:color/white"  
    android:orientation="vertical" >  
  
    <FrameLayout  
        android:layout_width="fill_parent"  
        android:layout_height="0dp"  
        android:layout_weight="1" >  
  
        <ImageView  
            android:id="@+id/id_content"  
            android:layout_width="fill_parent"  
            android:layout_height="fill_parent"  
            android:layout_gravity="center"  
            android:layout_margin="10dp"  
            android:scaleType="centerCrop"  
            android:src="@drawable/ic_launcher" />  
    </FrameLayout>  
  
    <com.example.zhy_horizontalscrollview.MyHorizontalScrollView  
        android:id="@+id/id_horizontalScrollView"  
        android:layout_width="wrap_content"  
        android:layout_height="150dp"  
        android:layout_gravity="bottom"  
        android:background="@android:color/white"  
        android:scrollbars="none" >  
  
        <LinearLayout  
            android:id="@+id/id_gallery"  
            android:layout_width="wrap_content"  
            android:layout_height="wrap_content"  
            android:layout_gravity="center_vertical"  
            android:orientation="horizontal" >  
        </LinearLayout>  
    </com.example.zhy_horizontalscrollview.MyHorizontalScrollView>  
  
</LinearLayout>  

没任何变化，除了把类名改成了我们自定义的类~

2、为了和国际接轨，我们也搞个Adapter，类似BaseAdapter

package com.example.zhy_horizontalscrollview;  
  
import java.util.List;  
  
import android.content.Context;  
import android.view.LayoutInflater;  
import android.view.View;  
import android.view.ViewGroup;  
import android.widget.BaseAdapter;  
import android.widget.ImageView;  
import android.widget.TextView;  
  
public class HorizontalScrollViewAdapter  
{  
  
    private Context mContext;  
    private LayoutInflater mInflater;  
    private List<Integer> mDatas;  
  
    public HorizontalScrollViewAdapter(Context context, List<Integer> mDatas)  
    {  
        this.mContext = context;  
        mInflater = LayoutInflater.from(context);  
        this.mDatas = mDatas;  
    }  
  
    public int getCount()  
    {  
        return mDatas.size();  
    }  
  
    public Object getItem(int position)  
    {  
        return mDatas.get(position);  
    }  
  
    public long getItemId(int position)  
    {  
        return position;  
    }  
  
    public View getView(int position, View convertView, ViewGroup parent)  
    {  
        ViewHolder viewHolder = null;  
        if (convertView == null)  
        {  
            viewHolder = new ViewHolder();  
            convertView = mInflater.inflate(  
                    R.layout.activity_index_gallery_item, parent, false);  
            viewHolder.mImg = (ImageView) convertView  
                    .findViewById(R.id.id_index_gallery_item_image);  
            viewHolder.mText = (TextView) convertView  
                    .findViewById(R.id.id_index_gallery_item_text);  
  
            convertView.setTag(viewHolder);  
        } else  
        {  
            viewHolder = (ViewHolder) convertView.getTag();  
        }  
        viewHolder.mImg.setImageResource(mDatas.get(position));  
        viewHolder.mText.setText("some info ");  
  
        return convertView;  
    }  
  
    private class ViewHolder  
    {  
        ImageView mImg;  
        TextView mText;  
    }  
  
}  

3、下面先看用法：

package com.example.zhy_horizontalscrollview;  
  
import java.util.ArrayList;  
import java.util.Arrays;  
import java.util.List;  
  
import android.app.Activity;  
import android.graphics.Color;  
import android.os.Bundle;  
import android.view.View;  
import android.view.Window;  
import android.widget.ImageView;  
  
import com.example.zhy_horizontalscrollview.MyHorizontalScrollView.CurrentImageChangeListener;  
import com.example.zhy_horizontalscrollview.MyHorizontalScrollView.OnItemClickListener;  
  
public class MainActivity extends Activity  
{  
  
    private MyHorizontalScrollView mHorizontalScrollView;  
    private HorizontalScrollViewAdapter mAdapter;  
    private ImageView mImg;  
    private List<Integer> mDatas = new ArrayList<Integer>(Arrays.asList(  
            R.drawable.a, R.drawable.b, R.drawable.c, R.drawable.d,  
            R.drawable.e, R.drawable.f, R.drawable.g, R.drawable.h,  
            R.drawable.l));  
  
    @Override  
    protected void onCreate(Bundle savedInstanceState)  
    {  
        super.onCreate(savedInstanceState);  
        requestWindowFeature(Window.FEATURE_NO_TITLE);  
        setContentView(R.layout.activity_main);  
  
        mImg = (ImageView) findViewById(R.id.id_content);  
  
        mHorizontalScrollView = (MyHorizontalScrollView) findViewById(R.id.id_horizontalScrollView);  
        mAdapter = new HorizontalScrollViewAdapter(this, mDatas);  
        //添加滚动回调  
        mHorizontalScrollView  
                .setCurrentImageChangeListener(new CurrentImageChangeListener()  
                {  
                    @Override  
                    public void onCurrentImgChanged(int position,  
                            View viewIndicator)  
                    {  
                        mImg.setImageResource(mDatas.get(position));  
                        viewIndicator.setBackgroundColor(Color  
                                .parseColor("#AA024DA4"));  
                    }  
                });  
        //添加点击回调  
        mHorizontalScrollView.setOnItemClickListener(new OnItemClickListener()  
        {  
  
            @Override  
            public void onClick(View view, int position)  
            {  
                mImg.setImageResource(mDatas.get(position));  
                view.setBackgroundColor(Color.parseColor("#AA024DA4"));  
            }  
        });  
        //设置适配器  
        mHorizontalScrollView.initDatas(mAdapter);  
    }  
  
}  

用起来是不是有点像ListView，初始化数据适配器，然后设置数据适配器，然后就是设置各种回调~~
如果仅仅是一堆图片展示，类似商品切换，更见简单，就不需要设置滚动监听和点击监听了~
4、最后看自定义的MyHorizontalScrollView类

package com.example.zhy_horizontalscrollview;  
  
import java.util.HashMap;  
import java.util.Map;  
  
import android.content.Context;  
import android.graphics.Color;  
import android.util.AttributeSet;  
import android.util.DisplayMetrics;  
import android.util.Log;  
import android.view.MotionEvent;  
import android.view.View;  
import android.view.View.OnClickListener;  
import android.view.WindowManager;  
import android.widget.HorizontalScrollView;  
import android.widget.LinearLayout;  
  
public class MyHorizontalScrollView extends HorizontalScrollView implements  
        OnClickListener  
{  
  
    /** 
     * 图片滚动时的回调接口 
     *  
     * @author zhy 
     *  
     */  
    public interface CurrentImageChangeListener  
    {  
        void onCurrentImgChanged(int position, View viewIndicator);  
    }  
  
    /** 
     * 条目点击时的回调 
     *  
     * @author zhy 
     *  
     */  
    public interface OnItemClickListener  
    {  
        void onClick(View view, int pos);  
    }  
  
    private CurrentImageChangeListener mListener;  
  
    private OnItemClickListener mOnClickListener;  
  
    private static final String TAG = "MyHorizontalScrollView";  
  
    /** 
     * HorizontalListView中的LinearLayout 
     */  
    private LinearLayout mContainer;  
  
    /** 
     * 子元素的宽度 
     */  
    private int mChildWidth;  
    /** 
     * 子元素的高度 
     */  
    private int mChildHeight;  
    /** 
     * 当前最后一张图片的index 
     */  
    private int mCurrentIndex;  
    /** 
     * 当前第一张图片的下标 
     */  
    private int mFristIndex;  
    /** 
     * 当前第一个View 
     */  
    private View mFirstView;  
    /** 
     * 数据适配器 
     */  
    private HorizontalScrollViewAdapter mAdapter;  
    /** 
     * 每屏幕最多显示的个数 
     */  
    private int mCountOneScreen;  
    /** 
     * 屏幕的宽度 
     */  
    private int mScreenWitdh;  
  
  
    /** 
     * 保存View与位置的键值对 
     */  
    private Map<View, Integer> mViewPos = new HashMap<View, Integer>();  
  
    public MyHorizontalScrollView(Context context, AttributeSet attrs)  
    {  
        super(context, attrs);  
        // 获得屏幕宽度  
        WindowManager wm = (WindowManager) context  
                .getSystemService(Context.WINDOW_SERVICE);  
        DisplayMetrics outMetrics = new DisplayMetrics();  
        wm.getDefaultDisplay().getMetrics(outMetrics);  
        mScreenWitdh = outMetrics.widthPixels;  
    }  
  
    @Override  
    protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec)  
    {  
        super.onMeasure(widthMeasureSpec, heightMeasureSpec);  
        mContainer = (LinearLayout) getChildAt(0);  
    }  
  
    /** 
     * 加载下一张图片 
     */  
    protected void loadNextImg()  
    {  
        // 数组边界值计算  
        if (mCurrentIndex == mAdapter.getCount() - 1)  
        {  
            return;  
        }  
        //移除第一张图片，且将水平滚动位置置0  
        scrollTo(0, 0);  
        mViewPos.remove(mContainer.getChildAt(0));  
        mContainer.removeViewAt(0);  
          
        //获取下一张图片，并且设置onclick事件，且加入容器中  
        View view = mAdapter.getView(++mCurrentIndex, null, mContainer);  
        view.setOnClickListener(this);  
        mContainer.addView(view);  
        mViewPos.put(view, mCurrentIndex);  
          
        //当前第一张图片小标  
        mFristIndex++;  
        //如果设置了滚动监听则触发  
        if (mListener != null)  
        {  
            notifyCurrentImgChanged();  
        }  
  
    }  
    /** 
     * 加载前一张图片 
     */  
    protected void loadPreImg()  
    {  
        //如果当前已经是第一张，则返回  
        if (mFristIndex == 0)  
            return;  
        //获得当前应该显示为第一张图片的下标  
        int index = mCurrentIndex - mCountOneScreen;  
        if (index >= 0)  
        {  
//          mContainer = (LinearLayout) getChildAt(0);  
            //移除最后一张  
            int oldViewPos = mContainer.getChildCount() - 1;  
            mViewPos.remove(mContainer.getChildAt(oldViewPos));  
            mContainer.removeViewAt(oldViewPos);  
              
            //将此View放入第一个位置  
            View view = mAdapter.getView(index, null, mContainer);  
            mViewPos.put(view, index);  
            mContainer.addView(view, 0);  
            view.setOnClickListener(this);  
            //水平滚动位置向左移动view的宽度个像素  
            scrollTo(mChildWidth, 0);  
            //当前位置--，当前第一个显示的下标--  
            mCurrentIndex--;  
            mFristIndex--;  
            //回调  
            if (mListener != null)  
            {  
                notifyCurrentImgChanged();  
  
            }  
        }  
    }  
  
    /** 
     * 滑动时的回调 
     */  
    public void notifyCurrentImgChanged()  
    {  
        //先清除所有的背景色，点击时会设置为蓝色  
        for (int i = 0; i < mContainer.getChildCount(); i++)  
        {  
            mContainer.getChildAt(i).setBackgroundColor(Color.WHITE);  
        }  
          
        mListener.onCurrentImgChanged(mFristIndex, mContainer.getChildAt(0));  
  
    }  
  
    /** 
     * 初始化数据，设置数据适配器 
     *  
     * @param mAdapter 
     */  
    public void initDatas(HorizontalScrollViewAdapter mAdapter)  
    {  
        this.mAdapter = mAdapter;  
        mContainer = (LinearLayout) getChildAt(0);  
        // 获得适配器中第一个View  
        final View view = mAdapter.getView(0, null, mContainer);  
        mContainer.addView(view);  
  
        // 强制计算当前View的宽和高  
        if (mChildWidth == 0 && mChildHeight == 0)  
        {  
            int w = View.MeasureSpec.makeMeasureSpec(0,  
                    View.MeasureSpec.UNSPECIFIED);  
            int h = View.MeasureSpec.makeMeasureSpec(0,  
                    View.MeasureSpec.UNSPECIFIED);  
            view.measure(w, h);  
            mChildHeight = view.getMeasuredHeight();  
            mChildWidth = view.getMeasuredWidth();  
            Log.e(TAG, view.getMeasuredWidth() + "," + view.getMeasuredHeight());  
            mChildHeight = view.getMeasuredHeight();  
            // 计算每次加载多少个View  
            mCountOneScreen = mScreenWitdh / mChildWidth+2;  
  
            Log.e(TAG, "mCountOneScreen = " + mCountOneScreen  
                    + " ,mChildWidth = " + mChildWidth);  
              
  
        }  
        //初始化第一屏幕的元素  
        initFirstScreenChildren(mCountOneScreen);  
    }  
  
    /** 
     * 加载第一屏的View 
     *  
     * @param mCountOneScreen 
     */  
    public void initFirstScreenChildren(int mCountOneScreen)  
    {  
        mContainer = (LinearLayout) getChildAt(0);  
        mContainer.removeAllViews();  
        mViewPos.clear();  
  
        for (int i = 0; i < mCountOneScreen; i++)  
        {  
            View view = mAdapter.getView(i, null, mContainer);  
            view.setOnClickListener(this);  
            mContainer.addView(view);  
            mViewPos.put(view, i);  
            mCurrentIndex = i;  
        }  
  
        if (mListener != null)  
        {  
            notifyCurrentImgChanged();  
        }  
  
    }  
  
    @Override  
    public boolean onTouchEvent(MotionEvent ev)  
    {  
        switch (ev.getAction())  
        {  
        case MotionEvent.ACTION_MOVE:  
//          Log.e(TAG, getScrollX() + "");  
  
            int scrollX = getScrollX();  
            // 如果当前scrollX为view的宽度，加载下一张，移除第一张  
            if (scrollX >= mChildWidth)  
            {  
                loadNextImg();  
            }  
            // 如果当前scrollX = 0， 往前设置一张，移除最后一张  
            if (scrollX == 0)  
            {  
                loadPreImg();  
            }  
            break;  
        }  
        return super.onTouchEvent(ev);  
    }  
  
    @Override  
    public void onClick(View v)  
    {  
        if (mOnClickListener != null)  
        {  
            for (int i = 0; i < mContainer.getChildCount(); i++)  
            {  
                mContainer.getChildAt(i).setBackgroundColor(Color.WHITE);  
            }  
            mOnClickListener.onClick(v, mViewPos.get(v));  
        }  
    }  
  
    public void setOnItemClickListener(OnItemClickListener mOnClickListener)  
    {  
        this.mOnClickListener = mOnClickListener;  
    }  
  
    public void setCurrentImageChangeListener(  
            CurrentImageChangeListener mListener)  
    {  
        this.mListener = mListener;  
    }  
  
}  

首先，加载第一个Item，根据item的宽计算当前屏幕可以加载多少张图片，然后初始化第一屏的图片，接下来就是从写onTouchEvent，在其中监听用户的ACTION_MOVE，然后根据移动的距离加载前一张或者后一张，同时动态移除不可见的View，回收内存~~~~
代码中有个Map专门存储View和posion的，主要是为了给点击回调提供当前的View的位置，有点类似：Android 自定义 ViewPager 打造千变万化的图片切换效果里面的Map的巧妙用法~~
是不是完全实现了ViewPager和HorizontalScrollView的合体~~_{**HorizontalScrollView的效果，ViewPager的特性}~~~**
最后贴一下旋转屏幕后的效果图：

如果你的项目中需要用到Gallery类似的效果，果断使用上例尝试吧~~

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