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 < -1) { // [-Infinity,-1)
                // This page is way off-screen to the left.
                view.setAlpha(0);

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

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

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

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

            } else { // (1,+Infinity]
                // This page is way off-screen to the right.
                view.setAlpha(0);
            }
        }
    }

    @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 5;
    }
}

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(-1 * 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>