℃江让您从精通到入门：Android Studio 简单实现ViewPager，可做APP操作提示

• 前期准备，如下图：
• 第一步、先书写布局文件：activity_main.xml文件如下：

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent">

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

    android.support.v4.view.ViewPager>

RelativeLayout>

• 第二步、在MainAvtivity中声明控件并使用自带的适配器操作List的方式，操作页面切换。MainActivity代码如下：

package com.example.dujiang0311.viewpager;

import android.support.v4.view.PagerAdapter;
import android.support.v4.view.ViewPager;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;
import android.view.ViewGroup;
import android.widget.ImageView;

import java.util.ArrayList;
import java.util.List;

public class MainActivity extends AppCompatActivity {

    private ViewPager mViewPager;
    private int[] mImgId = new int[]{R.drawable.p1, R.drawable.p2, R.drawable.p3};

    private List mList = new ArrayList<>();

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        mViewPager = (ViewPager) findViewById(R.id.viewpager);
        //为ViewPager添加动画效果
        mViewPager.setPageTransformer(true,new ZoomOutPageTransformer());
        mViewPager.setAdapter(new PagerAdapter() {

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

            @Override
            public Object instantiateItem(ViewGroup container, int position) {
                ImageView imageView = new ImageView(MainActivity.this);
                imageView.setImageResource(mImgId[position]);
                imageView.setScaleType(ImageView.ScaleType.CENTER_CROP);
                container.addView(imageView);
                mList.add(imageView);
                return imageView;
            }

            @Override
            public int getCount() {
                return mImgId.length;
            }

            @Override
            public boolean isViewFromObject(View view, Object object) {
                return view == object;
            }
        });
    }
}

• 动画切换类的书写（官方文档的例子）：ZoomOutPageTransformer代码书写如下：

package com.example.dujiang0311.viewpager;

/**
 * 项目名：  ViewPager
 * 包名：    com.example.dujiang0311.viewpager
 * 创建者：  Dujiang0311
 * 创建时间：2017/4/23 19:38
 * 描述：    TODO
 */

import android.annotation.SuppressLint;
import android.support.v4.view.ViewPager;
import android.util.Log;
import android.view.View;

public class ZoomOutPageTransformer implements ViewPager.PageTransformer
{
    private static final float MIN_SCALE = 0.85f;
    private static final float MIN_ALPHA = 0.5f;

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

        Log.e("TAG", view + " , " + position + "");

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

        } else if (position <= 1) //a页滑动至b页 ； a页从 0.0 -1 ；b页从1 ~ 0.0
        { // [-1,1]
            // Modify the default slide transition to shrink the page as well
            float scaleFactor = Math.max(MIN_SCALE, 1 - Math.abs(position));
            float vertMargin = pageHeight * (1 - scaleFactor) / 2;
            float horzMargin = pageWidth * (1 - scaleFactor) / 2;
            if (position < 0)
            {
                view.setTranslationX(horzMargin - vertMargin / 2);
            } else
            {
                view.setTranslationX(-horzMargin + vertMargin / 2);
            }

            // 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)
                    / (1 - MIN_SCALE) * (1 - MIN_ALPHA));

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

• 注意：如果想做闪屏的操作提示模块，可以在FlashActivity中加判断，判断用户是否是第一次打开APP，然后就可以了。