Android通过ViewPager实现左右滑动切换图片

想开发像人人网相册打开单张图片时候能左右滑动切换图片的效果，开始通过FlipperView实现，不能跟手拖动，效果不好，而且需要自己写很多代码来控制FlipperView中的View。后来发现Android 3.0之后的SDK中提供了android-support-v4包用以实现版本兼容，让老版本系统下的应用通过加入jar包实现扩展，得到新版的各种技术优势，例如Fragment等。



ViewPager是android-support-v4.jar包中的一个系统控件，继承自ViewGroup，专门用以实现左右滑动切换View的效果，使用时需要首先在Project->properties->Java Build Path->Libraries->Add External Jars中加入sdk目录下的extras/android/support/v4/android-support-v4.jar（如果找不到，则需要用sdk manager下载android support package）。加入这个jar包之后就可以使用ViewPager类了。



ViewPager的使用类似于ListView，需要有对应的Adapter进行数据绑定，实现图片切换仅需要继承PaperAdapter就可以了。继承后需要重写如下四个方法。





instantiateItem(ViewGroup, int)
destroyItem(ViewGroup, int, Object)
getCount()
isViewFromObject(View, Object)
类似于BaseAdapter，其中instantiateItem方法用来得到每个View，destroyItem用以控制当某个View不需要的时候的回收处理。isViewFromObject用来实现判断View和Object是否为同一个View。


Java代码 
import java.io.FileNotFoundException;  
import java.util.List;  
 
import android.content.Context;  
import android.graphics.Bitmap;  
import android.net.Uri;  
import android.support.v4.view.PagerAdapter;  
import android.support.v4.view.ViewPager;  
import android.view.View;  
import android.view.ViewGroup;  
import android.widget.ImageView;  
 
public class TestAdapter extends PagerAdapter {  
 
    private List<String> mPaths;  
      
    private Context mContext;  
      
    public TestAdapter(Context cx) {  
        mContext = cx.getApplicationContext();  
    }  
      
    public void change(List<String> paths) {  
        mPaths = paths;  
    }  
      
    @Override 
    public int getCount() {  
        // TODO Auto-generated method stub  
        return mPaths.size();  
    }  
 
    @Override 
    public boolean isViewFromObject(View view, Object obj) {  
        // TODO Auto-generated method stub  
        return view == (View) obj;  
    }  
 
    @Override 
    public Object instantiateItem (ViewGroup container, int position) {  
        ImageView iv = new ImageView(mContext);  
        try {  
            Bitmap bm = BitmapFactory.decodeFile(mPaths.get(position));//载入bitmap  
            iv.setImageBitmap(bm);  
        } catch (FileNotFoundException e) {  
            // TODO Auto-generated catch block  
            e.printStackTrace();  
        } catch (OutOfMemoryError e) {  
            // TODO Auto-generated catch block  
            e.printStackTrace();  
        }  
        ((ViewPager)container).addView(iv, 0);  
        return iv;  
    }  
      
    @Override 
    public void destroyItem (ViewGroup container, int position, Object object) {  
        container.removeView((View)object);  
    }  
} 

import java.io.FileNotFoundException;
import java.util.List;

import android.content.Context;
import android.graphics.Bitmap;
import android.net.Uri;
import android.support.v4.view.PagerAdapter;
import android.support.v4.view.ViewPager;
import android.view.View;
import android.view.ViewGroup;
import android.widget.ImageView;

public class TestAdapter extends PagerAdapter {

private List<String> mPaths;

private Context mContext;

public TestAdapter(Context cx) {
mContext = cx.getApplicationContext();
}

public void change(List<String> paths) {
mPaths = paths;
}

@Override
public int getCount() {
// TODO Auto-generated method stub
return mPaths.size();
}

@Override
public boolean isViewFromObject(View view, Object obj) {
// TODO Auto-generated method stub
return view == (View) obj;
}

@Override
public Object instantiateItem (ViewGroup container, int position) {
ImageView iv = new ImageView(mContext);
try {
Bitmap bm = BitmapFactory.decodeFile(mPaths.get(position));//载入bitmap
iv.setImageBitmap(bm);
} catch (FileNotFoundException e) {
// TODO Auto-generated catch block
e.printStackTrace();
} catch (OutOfMemoryError e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
((ViewPager)container).addView(iv, 0);
return iv;
}

@Override
public void destroyItem (ViewGroup container, int position, Object object) {
container.removeView((View)object);
}
}

Xml代码 
<android.support.v4.view.ViewPager 
    android:id="@+id/pager" 
    android:layout_width="fill_parent" 
    android:layout_height="fill_parent" /> 

    <android.support.v4.view.ViewPager
        android:id="@+id/pager"
        android:layout_width="fill_parent"
        android:layout_height="fill_parent" />

Activity:
Java代码 
@Override 
public void onCreate(Bundle savedInstanceState) {  
    super.onCreate(savedInstanceState);  
    setContentView(R.layout.main);  
    mViewPager = (ViewPager)findViewById(R.id.pager);  
    mAdapter = new TestAdapter(this);  
    mViewPager.setAdapter(mAdapter);  
    mAdapter.change(getList());  
}  
 
private List<String> getList() {  
    List<String> list = new ArrayList<String>();  
    list.add("file:///sdcard/Sunset.jpg");  
    list.add("file:///sdcard/Winter.jpg");  
    list.add("file:///sdcard/Water lilies.jpg");  
    list.add("file:///sdcard/Blue hills.jpg");  
    return list;  
}