ViewPager(1)FragmentPagerAdapter

FragmentPagerAdapter 适合只有少量的pager，所有pager同时全部存在，不会有被销毁的，page过多很容易内存溢出.

1，代码

1.1 ViewPagerMain.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;

 public class ViewPagerMain 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/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 ,OnPageChangeListener
     ViewPager pager;
     ViewPagerAdapter pagerAdapter;
     ViewPager.SimpleOnPageChangeListener simpleOnPageChangeListener;

     //3，初始化pager
     void initPager(View v){
         //从layout.xml中初始化pager
         pager = (ViewPager) v.findViewById(R.id.view_pager);

         //初始化page adapter
         pagerAdapter = new ViewPagerAdapter(getFragmentManager());

         //设置adapter
         pager.setAdapter(pagerAdapter);

         //设置page切换监听者
         simpleOnPageChangeListener = new ViewPager.SimpleOnPageChangeListener();
         pager.addOnPageChangeListener(simpleOnPageChangeListener);

         //设置pager切换动画
         pager.setPageTransformer(true, new DepthPageTransformer());

     }

     //4，处理 pager 切换事件
     //这里用的ViewPager.SimpleOnPageChangeListener,它什么也不做。

     //5，重写切换动画类，可以把这个类放到外面去。
     public class DepthPageTransformer implements ViewPager.PageTransformer {
         private static final float MIN_SCALE = 0.75f;

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

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

             } else if (position <= ) { // [-1,0]
                 // Use the default slide transition when moving to the left page
                 view.setAlpha();
                 view.setTranslationX();
                 view.setScaleX();
                 view.setScaleY();

             } else if (position <= ) { // (0,1]
                 // Fade the page out.
                 view.setAlpha( - position);

                 // Counteract the default slide transition
                 view.setTranslationX(pageWidth * -position);

                 // Scale the page down (between MIN_SCALE and 1)
                 float scaleFactor = MIN_SCALE
                         + ( - MIN_SCALE) * ( - Math.abs(position));
                 view.setScaleX(scaleFactor);
                 view.setScaleY(scaleFactor);

             } 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_pager_main, container, false);

         initPager(v);

         return v;
     }
 }

1.2 ViewPagerAdapter.java

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

 public class ViewPagerAdapter extends FragmentPagerAdapter{

     /*
     适合只有少量的pager，所有pager同时全部存在，不会有被销毁的，page过多很容易内存溢出.
     */
     public ViewPagerAdapter(FragmentManager fm) {
         super(fm);
     }

     @Override
     public Fragment getItem(int position) {
         System.out.println("getItem:create fragment");
         ViewPagerFragment fragment = new ViewPagerFragment();
         Bundle args = new Bundle();
         args.putInt("ID",position);
         fragment.setArguments(args);
         return fragment;
     }

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

1.3 ViewPagerFragment.java

 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 ViewPagerFragment extends Fragment {

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

     @Override
     public View onCreateView(LayoutInflater inflater, ViewGroup container,
                              Bundle savedInstanceState) {
         // Inflate the layout for this fragment
         View v = inflater.inflate(R.layout.fragment_pager, container, false);
         TextView tv = (TextView) v.findViewById(R.id.view_pager_content);
         Bundle args = getArguments();
         int position = args.getInt("ID");
         tv.setText("ViewPagerFragment " + position);
         v.setTranslationX(- * v.getWidth() * position);
         return v;
     }

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

 }

2，xml

2.1 fragment_pager_main.xml

 <?xml version="1.0" encoding="utf-8"?>
 <android.support.v4.view.ViewPager
     android:id="@+id/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_pager.xml

 <FrameLayout 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="#FFFFFF"
              tools:context=".ViewPager.ViewPagerFragment">

     <TextView
         android:id="@+id/view_pager_txt"
         android:layout_width="match_parent"
         android:layout_height="wrap_content"
         android:text="适合只有少量的pager，所有pager同时全部存在，不会有被销毁的，page过多很容易内存溢出.\n可以在LogCat中查看page对应的Fragment\n的onCreate,onDestory"/>

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

 </FrameLayout>