OnPageChangeListener的简单运用

参考自博客:http://www.cnblogs.com/xinye/archive/2013/06/09/3128209.html

目的:

     进一步简单熟悉OnPageChangeListener, ViewPager浏览图片时候切换页面的时候有个缩放效果。

     这里主要用了setPadding(...) 同理可以增加setAlpha(...)透明度改变的效果。

代码一: activity_main.xml

<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"
    tools:context="${relativePackage}.${activityClass}" >
  <android.support.v4.view.ViewPager
      android:layout_width="match_parent"
      android:layout_height="match_parent"
      android:id="@+id/viewPager"  />
</LinearLayout>

代码二: MainActivity.java

public class MainActivity extends Activity {
   private ViewPager mViewPager;
	@Override
	protected void onCreate(Bundle savedInstanceState) {
		super.onCreate(savedInstanceState);
		setContentView(R.layout.activity_main);
		mViewPager=(ViewPager)findViewById(R.id.viewPager);
		Integer[] drawableArray=new Integer[]{
				R.drawable.dongzhi,R.drawable.hanlu
				,R.drawable.liqiu,R.drawable.xiaohan
		};
		ArrayList<ImageView> list=new ArrayList<ImageView>();
		for(int i=0;i<drawableArray.length;i++){
			ImageView imgView=new ImageView(this);
			imgView.setImageResource(drawableArray[i]);
			list.add(imgView);
		}
		mViewPager.setAdapter(new mViewPagerAdapter(list));
		mPageChangeListener listener=new mPageChangeListener(mViewPager,list);
		mViewPager.setOnPageChangeListener(listener);
	}

        // Part2-->>Adapter适配器
	class mViewPagerAdapter extends PagerAdapter{
		private ArrayList<ImageView> viewList;
		public mViewPagerAdapter(ArrayList<ImageView> viewList){
			this.viewList=viewList;
		}
		@Override
		public int getCount() {
			return viewList.size();
		}

		@Override
		public boolean isViewFromObject(View view, Object obj) {
			return view==obj;
		}
		@Override
		public void destroyItem(ViewGroup container, int position, Object object) {
			container.removeViewInLayout((View) object);
		}
		@Override
		public Object instantiateItem(ViewGroup container, int position) {
			ImageView imgView=viewList.get(position);
			container.addView(imgView);
			return  imgView;
		}
	}

          //Part3 - ->>OnPageChangeListener监听类
	  class mPageChangeListener implements OnPageChangeListener{
		  int currentPageNo=0;
		  int offset=0;
		  int downX=0;
		  private ArrayList<ImageView> viewList;
		  private ViewPager viewPager;
        public mPageChangeListener(ViewPager viewPager,ArrayList<ImageView>list){
        	this.viewPager=viewPager;
        	this.viewList=list;
        	this.viewPager.setOnTouchListener(new OnTouchListener(){
				@Override      
				//本来想根据OnTouchListener对第0页和最后一页做处理的，结果。。。没弄出来，这里没有用到这个监听类
				public boolean onTouch(View v, MotionEvent event) {
				   switch(event.getAction()){
				   case MotionEvent.ACTION_DOWN: downX=(int) event.getX(); break;
				   case MotionEvent.ACTION_MOVE:
					   offset=(int)(event.getX()-downX); break;
				   case MotionEvent.ACTION_UP:
					   offset=0; downX=0; break;
				   }
					return false;//false则go on,true则不会继续响应ViewPager本身的触摸事件机制;
				}
        	});
        }
		@Override
		public void onPageScrollStateChanged(int state) {
			if(state==ViewPager.SCROLL_STATE_IDLE){
				for(int i=0;i<viewList.size()-1;i++){
			 viewList.get(i).setPadding(0, 0, 0, 0);
				}
			}
			Log.v("zz","zz-->>State="+state);
		}
		@Override
		public void onPageScrolled(int position, float positionOffset, int positionOffsetPixels) {
			Log.v("zz","zz-->>position="+position+"--Offset="+positionOffset+"--offsetPixels="+positionOffsetPixels);
            int paddingNum=50;
            int paddingNext=(int)(paddingNum*(1-positionOffset));
            int paddingCurr=(int)(paddingNum*positionOffset);
            if(position!=viewList.size()-1){
            	viewList.get(position).setPadding(paddingCurr, paddingCurr, paddingCurr, paddingCurr);
            	viewList.get(position+1).setPadding(paddingNext, paddingNext, paddingNext, paddingNext);
            	//第N页滑向第N+1页 position=N;第N+1页滑向第N页，position=N;
            }
		}
		@Override
		public void onPageSelected(int position) {
		}
	  }
}

截图: