ViewPager(2)FragmentStatePagerAdapter示例

　　

　　FragmentStatePagerAdapter适用于数量比较大的viewPager,只会存在 前1个fragment 当前fragment 和下1个fragment，其他销毁，适合加载多数据。本例中有100个pager .

1.代码

1.1 StateViewPagerMain.java

 import android.os.Bundle;
 import android.support.v4.app.Fragment;
 import android.support.v4.view.ViewPager;
 import android.view.LayoutInflater;
 import android.view.View;
 import android.view.ViewGroup;

 import com.txw.e.viewpager.R;

 /**
  * A simple {@link Fragment} subclass.
  */
 public class StateViewPagerMain extends Fragment {

     //1，在layout.xml中添加 ViewPagerFragment,它可以是顶级布局，如下：
     /*
     <?xml version="1.0" encoding="utf-8"?>
     <android.support.v4.view.ViewPagerFragment
         android:id="@+id/state_view_pager"
         xmlns:android="http://schemas.android.com/apk/res/android"
         android:layout_width="match_parent"
         android:layout_height="match_parent"/>
     */

     //2，准备变量,ViewPager和PagerAdapter（本例中是FragmentStatePagerAdapter）
     ViewPager statePager;
     StateViewPagerAdapter pagerAdapter;

     //3，初始化view pager及 adapter
     void initViewPager(View v){
         //初始化pager
         statePager = (ViewPager) v.findViewById(R.id.state_view_pager);

         //构造PageAdapter
         pagerAdapter = new StateViewPagerAdapter(getFragmentManager());
         statePager.setAdapter(pagerAdapter);

         //设置page 切换的监听器
         statePager.addOnPageChangeListener(pageChangeListener);

         //设置pager切换时的动画
         statePager.setPageTransformer(true, new ZoomOutPageTransformer());
     }

     //4，处理page的切换事件
     ViewPager.OnPageChangeListener pageChangeListener = new ViewPager.OnPageChangeListener() {
         @Override
         public void onPageScrolled(int position, float positionOffset, int positionOffsetPixels) {
             System.out.println("onPageScrolled " + position);
             System.out.println("positionOffset " + positionOffset);
             System.out.println("positionOffsetPixels " + positionOffsetPixels);
         }

         @Override
         public void onPageSelected(int position) {
             System.out.println("onPageSelected " + position);
         }

         @Override
         public void onPageScrollStateChanged(int state) {
             System.out.println("onPageScrollStateChanged " + state);
         }
     };

     //5，pager之间动画切换类
     public class ZoomOutPageTransformer implements ViewPager.PageTransformer {
         private static final float MIN_SCALE = 0.85f;
         private static final float MIN_ALPHA = 0.5f;

         public void transformPage(View view, float position) {
             int pageWidth = view.getWidth();
             int pageHeight = view.getHeight();

             if (position < -) { // [-Infinity,-1)
                 // This page is way off-screen to the left.
                 view.setAlpha();

             } else if (position <= ) { // [-1,1]
                 // Modify the default slide transition to shrink the page as well
                 float scaleFactor = Math.max(MIN_SCALE,  - Math.abs(position));
                 float vertMargin = pageHeight * ( - scaleFactor) / ;
                 float horzMargin = pageWidth * ( - scaleFactor) / ;
                 if (position < ) {
                     view.setTranslationX(horzMargin - vertMargin / );
                 } else {
                     view.setTranslationX(-horzMargin + vertMargin / );
                 }

                 // Scale the page down (between MIN_SCALE and 1)
                 view.setScaleX(scaleFactor);
                 view.setScaleY(scaleFactor);

                 // Fade the page relative to its size.
                 view.setAlpha(MIN_ALPHA +
                         (scaleFactor - MIN_SCALE) /
                                 ( - MIN_SCALE) * ( - MIN_ALPHA));

             } else { // (1,+Infinity]
                 // This page is way off-screen to the right.
                 view.setAlpha();
             }
         }
     }
     @Override
     public View onCreateView(LayoutInflater inflater, ViewGroup container,
                              Bundle savedInstanceState) {
         // Inflate the layout for this fragment
         View v = inflater.inflate(R.layout.fragment_state_pager_main, container, false);

         initViewPager(v);

         return v;
     }
 }

1.2 StateViewPagerAdapter.java

 import android.os.Bundle;
 import android.support.v4.app.Fragment;
 import android.support.v4.app.FragmentManager;
 import android.support.v4.app.FragmentStatePagerAdapter;

 public class StateViewPagerAdapter extends FragmentStatePagerAdapter {

     /*
     FragmentStatePagerAdapter适用于数量比较大的viewPager,
     只会存在 前1个fragment 当前fragment 和下1个fragment，其他销毁，适合加载多数据。
     */
     public StateViewPagerAdapter(FragmentManager fm) {
         super(fm);
     }

     @Override
     public Fragment getItem(int position) {
         System.out.println("Fragment " + position + " created");
         StateViewPagerFragment fragment = new StateViewPagerFragment();
         Bundle args = new Bundle();
         args.putInt("ID",position);

         fragment.setArguments(args);
         return fragment;
     }

     @Override
     public int getCount() {
         return ;
     }
 }

1.3 StateViewPagerFragment.java

 import android.graphics.Color;
 import android.os.Bundle;
 import android.support.v4.app.Fragment;
 import android.view.LayoutInflater;
 import android.view.View;
 import android.view.ViewGroup;
 import android.widget.TextView;

 import com.txw.e.viewpager.R;

 public class StateViewPagerFragment extends Fragment {

     @Override
     public View onCreateView(LayoutInflater inflater, ViewGroup container,
                              Bundle savedInstanceState) {
         // Inflate the layout for this fragment
         View v = inflater.inflate(R.layout.fragment_state_pager, container, false);
         v.setBackgroundColor(Color.parseColor("#FFFFFF"));
         Bundle args = getArguments();
         TextView tv = (TextView) v.findViewById(R.id.state_view_pager_content);
         tv.setText("Fragment : " + args.getInt("ID"));
         return v;
     }

     @Override
     public void onCreate(Bundle savedInstanceState) {
         super.onCreate(savedInstanceState);
         System.out.println("StateViewPagerFragment" + getArguments().getInt("ID") + "::onCreate()");
     }
     @Override
     public void onDestroy() {
         super.onDestroy();
         System.out.println("StateViewPagerFragment" + getArguments().getInt("ID") + "::onDestroy()");
     }
 }

2.xml

2.1 fragment_state_pager_main.xml

 <?xml version="1.0" encoding="utf-8"?>
 <android.support.v4.view.ViewPager
     android:id="@+id/state_view_pager"
     xmlns:android="http://schemas.android.com/apk/res/android"
     android:background="#FFFFFF"
     android:layout_width="match_parent"
     android:layout_height="match_parent"/>

2.2 fragment_state_pager.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"
               android:orientation="vertical"
               tools:context=".StateViewPager.StateViewPagerFragment">

     <TextView
         android:id="@+id/state_view_pager_txt"
         android:layout_width="match_parent"
         android:layout_height="wrap_content"
         android:text="  FragmentStatePagerAdapter适用于数量比较大的viewPager,\n  只会存在 前1个fragment 当前fragment 和下1个fragment，其他销毁，适合加载多数据。本例中有100个pager。\n可以在LogCat中查看page对应的Fragment\n的onCreate,onDestory"/>

     <TextView
         android:id="@+id/state_view_pager_content"
         android:layout_width="match_parent"
         android:layout_height="match_parent"
         android:gravity="center_horizontal|center_vertical"
         android:layout_gravity="center_horizontal|center_vertical"
         android:text="@string/hello_blank_fragment"/>

 </LinearLayout>