Android -- 使用ViewPager实现画廊效果

1，今天在微信推送文章看到实现画廊效果，感觉挺不错的，就来写写试试，先来看一下效果图：

上面的效果基本上可以用两个功能点来包含：ViewPager的切换动画、ImageView的倒影的实现

嗯，先来将我们主要的功能来实现，就是我们的ViewPager展示图片

主界面的布局：

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:id="@+id/activity_main"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:background="@android:color/white"
    android:clipChildren="false"
    android:layerType="software"
    android:orientation="vertical"
    tools:context="com.qianmo.gallerythreed.MainActivity">

    <android.support.v4.view.ViewPager
        android:id="@+id/viewPager"
        android:layout_width="wrap_content"
        android:layout_height="400dp"
        android:layout_gravity="center"
        android:clipChildren="false"
        >
    </android.support.v4.view.ViewPager>
</LinearLayout>

这里要注意以下 android:clipChildren="false" 这句代码的含义，就是不限制View的布局

自定义适配器，继承于PagerAdapter

package com.qianmo.gallerythreed.adapter;

import android.support.v4.view.PagerAdapter;
import android.view.View;
import android.view.ViewGroup;
import android.widget.ImageView;

import java.util.List;

/**
 * Created by Administrator on 2016/10/20 0020.
 */
public class MyViewPagerAdapter extends PagerAdapter {
    private List<ImageView> listViews;

    public MyViewPagerAdapter(List<ImageView> listViews) {
        this.listViews = listViews;
    }

    @Override
    public int getCount() {
        return listViews == null ? 0 : listViews.size();
    }

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

    @Override
    public Object instantiateItem(ViewGroup container, int position) {
        ImageView imageView = listViews.get(position);
        container.addView(imageView);
        return imageView;
    }

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

这是最基本的框架，再来了解一下我们PageTransformer这个类 ，它是ViewPager的一个公共成员接口。当然，由于是通过属性动画来设置的，所以设置的pagetransformer在Android3.0以下会被忽略。这里普及一个常识，当我们ViewPager的当前Item在左右滑动的时候其实其position是在【-1,1】这个区间变换的，当View向做滑动时在【-1,0】之间滑动，当View向右滑动时在【0，1】之间变化，所以我们可以自定义PageTransformer类来实现我们滑动的切换动画

package com.qianmo.gallerythreed.pageTransformer;

import android.support.v4.view.ViewPager.PageTransformer;
import android.view.View;

/**
 * Created by wangjitao on 2016/10/20 0020.
 * 实现Viewpager的翻页效果
 */
public class GallyPageTransformer implements PageTransformer {
    private static final float min_scale = 0.85f;

    @Override
    public void transformPage(View page, float position) {
        float scaleFactor = Math.max(min_scale, 1 - Math.abs(position));
        float rotate = 20 * Math.abs(position);
        if (position < -1) {

        } else if (position < 0) {
            page.setScaleX(scaleFactor);
            page.setScaleY(scaleFactor);
            page.setRotationY(rotate);
        } else if (position >= 0 && position < 1) {
            page.setScaleX(scaleFactor);
            page.setScaleY(scaleFactor);
            page.setRotationY(-rotate);
        } else if (position >= 1) {
            page.setScaleX(scaleFactor);
            page.setScaleY(scaleFactor);
            page.setRotationY(-rotate);
        }
    }
}

注意 viewpager设置setPageTransformer（）方法一定要在setAdapter（）方法之前，OK，这样的话我们就实现了第一个小的功能，再来实现图片倒影的效果，直接上代码

package com.qianmo.gallerythreed.utils;

/**
 * Created by Administrator on 2016/10/20 0020.
 */

import android.content.Context;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.LinearGradient;
import android.graphics.Matrix;
import android.graphics.Paint;
import android.graphics.PorterDuff;
import android.graphics.PorterDuffXfermode;
import android.graphics.Shader;

/**
 * Created by Administrator on 2016/8/20.
 * 图片倒影工具类
 */

public class ImageUtil {
    public static Bitmap getReverseBitmapById(int resId, Context context){
        Bitmap sourceBitmap= BitmapFactory.decodeResource(context.getResources(),resId);
        //绘制原图的下一半图片
        Matrix matrix=new Matrix();
        //倒影翻转
        matrix.setScale(1,-1);

        Bitmap inverseBitmap=Bitmap.createBitmap(sourceBitmap,0,sourceBitmap.getHeight()/2,sourceBitmap.getWidth(),sourceBitmap.getHeight()/3,matrix,false);
        //合成图片
        Bitmap groupbBitmap=Bitmap.createBitmap(sourceBitmap.getWidth(),sourceBitmap.getHeight()+sourceBitmap.getHeight()/3+60,sourceBitmap.getConfig());
        //以合成图片为画布
        Canvas gCanvas=new Canvas(groupbBitmap);
        //将原图和倒影图片画在合成图片上
        gCanvas.drawBitmap(sourceBitmap,0,0,null);
        gCanvas.drawBitmap(inverseBitmap,0,sourceBitmap.getHeight()+50,null);
        //添加遮罩
        Paint paint=new Paint();
        Shader.TileMode tileMode= Shader.TileMode.CLAMP;
        LinearGradient shader=new LinearGradient(0,sourceBitmap.getHeight()+50,0,
                groupbBitmap.getHeight(), Color.BLACK,Color.TRANSPARENT,tileMode);
        paint.setShader(shader);
        //这里取矩形渐变区和图片的交集
        paint.setXfermode(new PorterDuffXfermode(PorterDuff.Mode.DST_IN));
        gCanvas.drawRect(0,sourceBitmap.getHeight()+50,sourceBitmap.getWidth(),groupbBitmap.getHeight(),paint);
        return groupbBitmap;
    }
}

这个倒影的效果真心不推荐  ，一下子我图片就OOM了，这样我们就全都实现了  ，最后贴出MainActivity的代码

package com.qianmo.gallerythreed;

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

import com.qianmo.gallerythreed.adapter.MyViewPagerAdapter;
import com.qianmo.gallerythreed.pageTransformer.GallyPageTransformer;
import com.qianmo.gallerythreed.utils.ImageUtil;

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

public class MainActivity extends AppCompatActivity {

    private ViewPager mViewPager;
    private LinearLayout ll_main;
    private List<ImageView> imageViews;
    private int pagerWidth;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        mViewPager = (ViewPager) findViewById(R.id.viewPager);
        ll_main = (LinearLayout) findViewById(R.id.activity_main);
        initData();

        mViewPager.setOffscreenPageLimit(3);
        pagerWidth = (int) (getResources().getDisplayMetrics().widthPixels * 3.0f / 5.0f);
        ViewGroup.LayoutParams lp = mViewPager.getLayoutParams();
        if (lp == null) {
            lp = new ViewGroup.LayoutParams(pagerWidth, ViewGroup.LayoutParams.MATCH_PARENT);
        } else {
            lp.width = pagerWidth;
        }
        mViewPager.setLayoutParams(lp);
        mViewPager.setPageMargin(-50);
        ll_main.setOnTouchListener(new View.OnTouchListener() {
            @Override
            public boolean onTouch(View view, MotionEvent motionEvent) {
                return mViewPager.dispatchTouchEvent(motionEvent);
            }
        });
        mViewPager.setPageTransformer(true, new GallyPageTransformer());
        mViewPager.setAdapter(new MyViewPagerAdapter(imageViews));
    }

    private void initData() {
        imageViews = new ArrayList<>();
        ImageView first = new ImageView(MainActivity.this);
        first.setImageBitmap(ImageUtil.getReverseBitmapById(R.mipmap.first, MainActivity.this));
//        first.setImageResource(R.mipmap.first);
        ImageView second = new ImageView(MainActivity.this);
        second.setImageBitmap(ImageUtil.getReverseBitmapById(R.mipmap.second, MainActivity.this));
//        second.setImageResource(R.mipmap.second);
        ImageView third = new ImageView(MainActivity.this);
        third.setImageBitmap(ImageUtil.getReverseBitmapById(R.mipmap.third, MainActivity.this));
//        third.setImageResource(R.mipmap.third);
        ImageView fourth = new ImageView(MainActivity.this);
//        fourth.setImageBitmap(ImageUtil.getReverseBitmapById(R.mipmap.fourth,MainActivity.this));
        fourth.setImageResource(R.mipmap.fourth);
        ImageView fifth = new ImageView(MainActivity.this);
        fifth.setImageBitmap(ImageUtil.getReverseBitmapById(R.mipmap.fifth, MainActivity.this));
//        fifth.setImageResource(R.mipmap.fifth);
        imageViews.add(first);
        imageViews.add(second);
        imageViews.add(third);
        imageViews.add(fourth);
        imageViews.add(fifth);
    }
}