PageTransformer实现个性的ViewPager切换动画

泡在网上的日子 / 文 发表于2014-10-30 15:12 次阅读 ViewPager

转自: 鸿洋的博客


ViewPager自带了一个setPageTransformer用于设置切换动画~

本篇博文,将:

1、介绍如何使用setPageTransformer设置切换动画;

2、自定义PageTransformer实现个性的切换动画;

3、该方法在SDK11以下的版本不起作用,我们会对其做一定修改,让其向下兼容。

官方示例地址:http://developer.android.com/training/animation/screen-slide.html 有兴趣的可以去看看~~


好了,下面开始编写代码~~

2、setPageTransformer的使用

首先我们迅速的实现一个传统的ViewPager效果~

1、布局文件

<RelativeLayout 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.support.v4.view.ViewPager
        android:id="@+id/id_viewpager"
        android:layout_width="fill_parent"
        android:layout_height="fill_parent" />
</RelativeLayout>

2、MainActivity

package com.zhy.demo_zhy_08_viewpageranim;
import java.util.ArrayList;
import java.util.List;
import android.app.Activity;
import android.os.Bundle;
import android.support.v4.view.PagerAdapter;
import android.support.v4.view.ViewPager;
import android.view.View;
import android.view.ViewGroup;
import android.view.Window;
import android.widget.ImageView;
import android.widget.ImageView.ScaleType;
public class MainActivity extends Activity
{
    private ViewPager mViewPager;
    private int[] mImgIds = new int[] { R.drawable.guide_image1,
            R.drawable.guide_image2, R.drawable.guide_image3 };
    private List<ImageView> mImageViews = new ArrayList<ImageView>();
    @Override
    protected void onCreate(Bundle savedInstanceState)
    {
        super.onCreate(savedInstanceState);
        requestWindowFeature(Window.FEATURE_NO_TITLE);
        setContentView(R.layout.activity_main);
        initData();
        mViewPager = (ViewPager) findViewById(R.id.id_viewpager);
        mViewPager.setAdapter(new PagerAdapter()
        {
            @Override
            public Object instantiateItem(ViewGroup container, int position)
            {
                container.addView(mImageViews.get(position));
                return mImageViews.get(position);
            }
            @Override
            public void destroyItem(ViewGroup container, int position,
                    Object object)
            {
                container.removeView(mImageViews.get(position));
            }
            @Override
            public boolean isViewFromObject(View view, Object object)
            {
                return view == object;
            }
            @Override
            public int getCount()
            {
                return mImgIds.length;
            }
        });
    }
    private void initData()
    {
        for (int imgId : mImgIds)
        {
            ImageView imageView = new ImageView(getApplicationContext());
            imageView.setScaleType(ScaleType.CENTER_CROP);
            imageView.setImageResource(imgId);
            mImageViews.add(imageView);
        }
    }
}

好了,这样一个传统ViewPager就实现了~~大家对上面代码应该不会有任何陌生的感觉~运行效果也不用贴图了,大家肯定知道~~

3、PageTransformer

ViewPager有个方法叫做:

setPageTransformer(boolean reverseDrawingOrder, PageTransformer transformer) 用于设置ViewPager切换时的动画效果,并且google官方还给出了两个示例。

只需要在上述代码中调用setPageTransformer即可添加切换动画效果~~下面演示google的两个PageTransformer的代码,以及运行效果。

1、DepthPageTransformer

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);
        }
    }
}

调用代码:

mViewPager.setPageTransformer(true, new DepthPageTransformer());

效果:


2、ZoomOutPageTransformer

package com.zhy.view;
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);
        }
    }
}

调用代码:

mViewPager.setPageTransformer(true, new ZoomOutPageTransformer());

效果:



效果图都是google官网上的,我们的测试图会在兼容3.0以下贴出来,不然就重复了~~

为ViewPager添加切换就一行代码是不是很happy,可惜是不兼容3.0以下的版本的,该方法的注释上写到:

setting a PageTransformer prior to Android 3.0 (API 11) will have no effect 在3.0之前的版本设置此方法是没有效果的,那么下面我们就看如何让其兼容3.0以下版本。

3、版本的向下兼容

1、不兼容的原因

首先看下为什么不兼容,3.0以下呢?

看上面的两个示例代码,代码中View的动画使用的是属性动画,而属性动画是3.0才推出的,那么这么写肯定是不兼容3.0以下了~

那么我们首先引入nineoldandroids,让动画先能在3.0以下跑再说:

修改DepthPageTransformer

package com.zhy.view;
import com.nineoldandroids.view.ViewHelper;
import android.annotation.SuppressLint;
import android.support.v4.view.ViewPager;
import android.view.View;
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);
            ViewHelper.setAlpha(view, 0);
        } else if (position <= 0)// a页滑动至b页 ; a页从 0.0 -1 ;b页从1 ~ 0.0
        { // [-1,0]
            // Use the default slide transition when moving to the left page
            // view.setAlpha(1);
            ViewHelper.setAlpha(view, 1);
            // view.setTranslationX(0);
            ViewHelper.setTranslationX(view, 0);
            // view.setScaleX(1);
            ViewHelper.setScaleX(view, 1);
            // view.setScaleY(1);
            ViewHelper.setScaleY(view, 1);
        } else if (position <= 1)
        { // (0,1]
            // Fade the page out.
            // view.setAlpha(1 - position);
            ViewHelper.setAlpha(view, 1 - position);
            // Counteract the default slide transition
            // view.setTranslationX(pageWidth * -position);
            ViewHelper.setTranslationX(view, pageWidth * -position);
            // Scale the page down (between MIN_SCALE and 1)
            float scaleFactor = MIN_SCALE + (1 - MIN_SCALE) * (1 - position);
            // view.setScaleX(scaleFactor);
            ViewHelper.setScaleX(view, scaleFactor);
            // view.setScaleY(1);
            ViewHelper.setScaleY(view, scaleFactor);
        } else
        { // (1,+Infinity]
            // This page is way off-screen to the right.
            // view.setAlpha(0);
            ViewHelper.setAlpha(view, 1);
        }
    }
}


很简单,把所有属性动画换成ViewHelper去设置就好了。现在我们去3.0以下的机子上去运行,发现还是没有效果~~~

为什么呢?

我们再去看看setPageTransformer的源码:

public void setPageTransformer(boolean reverseDrawingOrder, PageTransformer transformer) {
       if (Build.VERSION.SDK_INT >= 11) {
           final boolean hasTransformer = transformer != null;
           final boolean needsPopulate = hasTransformer != (mPageTransformer != null);
           mPageTransformer = transformer;
           setChildrenDrawingOrderEnabledCompat(hasTransformer);
           if (hasTransformer) {
               mDrawingOrder = reverseDrawingOrder ? DRAW_ORDER_REVERSE : DRAW_ORDER_FORWARD;
           } else {
               mDrawingOrder = DRAW_ORDER_DEFAULT;
           }
           if (needsPopulate) populate();
       }
   }

终于发现原因了,原来在此方法内部判断了如果是11以上的版本才让动画生效~~

那么,没办法了,如果想兼容,必须修改ViewPager的源码了~~

2、完美向下兼容

我们将ViewPager的源码拷贝一份至我们的项目中,修改名称为ViewPagerCompat;然后注释掉SDK版本判断那一句

public class ViewPagerCompat extends ViewGroup {
public void setPageTransformer(boolean reverseDrawingOrder, ViewPager.PageTransformer transformer) {
//        if (Build.VERSION.SDK_INT >= 11)
        {
            final boolean hasTransformer = transformer != null;
            final boolean needsPopulate = hasTransformer != (mPageTransformer != null);
            mPageTransformer = transformer;
            setChildrenDrawingOrderEnabledCompat(hasTransformer);
            if (hasTransformer) {
                mDrawingOrder = reverseDrawingOrder ? DRAW_ORDER_REVERSE : DRAW_ORDER_FORWARD;
            } else {
                mDrawingOrder = DRAW_ORDER_DEFAULT;
            }
            if (needsPopulate) populate();
        }
    }

...
}

注意,所有的PageTransformer使用ViewPager.PageTransformer

然后我们把项目中的ViewPager改为ViewPagerCompat;记得修改布局文件,以及MainActivity中的ViewPager为ViewPagerCompat

我们在2.3.3的模拟器上测试下效果:



可以看到,我们的切换动画完美的运行在2.3.3的机器上~~so happy ~~没有ViewPager源码的童鞋不要紧,我会在文末的源码下载中加入ViewPager源码,让你可以尽情去测试~~

当然了,仅仅是兼容当然不能满足我们的好奇心,难道我们做到了兼容,还只能使用Google给的示例动画么~~我们强大的创新呢~~下面带领大家分析setPageTransformer方法,然后设计一个个性的动画切换效果

4、自定义PageTransformer实现个性切换动画

public interface PageTransformer {
       /**
        * Apply a property transformation to the given page.
        *
        * @param page Apply the transformation to this page
        * @param position Position of page relative to the current front-and-center
        *                 position of the pager. 0 is front and center. 1 is one full
        *                 page position to the right, and -1 is one page position to the left.
        */
       public void transformPage(View page, float position);
   }

可以看到该接口只有一个方法,第一个是我们的view,第二个是position~~

当我们滑动时:会打印出当然ViewPager中存活的每个View以及它们的position的变化~~注意是每一个,所以建议别只log position,不然你会觉得莫名其妙的输出~~

position的可能性的值有,其实从官方示例的注释就能看出:

[-Infinity,-1)  已经看不到了

(1,+Infinity] 已经看不到了

[-1,1]

重点看[-1,1]这个区间 , 其他两个的View都已经看不到了~~


假设现在ViewPager在A页现在滑出B页,则:

A页的position变化就是( 0, -1]

B页的position变化就是[ 1 , 0 ]

知道了我们滑动时position的变化~~那么就开始设计我们的个性的切换效果;

官方给的例子,有变化透明度、偏移量、缩放的,我们准备来个不一样的,我们变化角度,即rotation;

大概的效果是这样的:


下面我们分析代码:

我们设置View的旋转中心为:

ViewHelper.setPivotX(view, view.getMeasuredWidth() * 0.5f);
ViewHelper.setPivotY(view, view.getMeasuredHeight());

依然是ViewPager在A页现在滑出B页

那么A页应当在滑动过程中0度到-20度的偏移,B页应当在滑动过程中+20度到0度的偏移

结合

A页的position变化就是( 0, -1]

B页的position变化就是[ 1 , 0 ]

那么旋转的角度即:mRot = (20 * position); A页 mRot :0 ,~ -20 ; B页 mRot :20 ~ 0  ;

瞬间觉得好简单:

完整代码:

package com.zhy.view;
import com.nineoldandroids.view.ViewHelper;
import android.annotation.SuppressLint;
import android.support.v4.view.ViewPager;
import android.util.Log;
import android.view.View;
public class RotateDownPageTransformer implements ViewPager.PageTransformer
{
                                                               
    private static final float ROT_MAX = 20.0f;
    private float mRot;
                                                               
                                                               
    public void transformPage(View view, float position)
    {
        Log.e("TAG", view + " , " + position + "");
        if (position < -1)
        { // [-Infinity,-1)
            // This page is way off-screen to the left.
            ViewHelper.setRotation(view, 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
            if (position < 0)
            {
                mRot = (ROT_MAX * position);
                ViewHelper.setPivotX(view, view.getMeasuredWidth() * 0.5f);
                ViewHelper.setPivotY(view, view.getMeasuredHeight());
                ViewHelper.setRotation(view, mRot);
            } else
            {
                mRot = (ROT_MAX * position);
                ViewHelper.setPivotX(view, view.getMeasuredWidth() * 0.5f);
                ViewHelper.setPivotY(view, view.getMeasuredHeight());
                ViewHelper.setRotation(view, mRot);
            }
            // Scale the page down (between MIN_SCALE and 1)
            // Fade the page relative to its size.
        } else
        { // (1,+Infinity]
            // This page is way off-screen to the right.
            ViewHelper.setRotation(view, 0);
        }
    }
}

你没看错,if else 里面代码是一样的,为了好理解特意没有合并到一起~~~


到此,我们从setPageTransformer使用,到修改ViewPager做到向下兼容,直至自己定义出个性的切换效果 都已经介绍完毕~~

大家可以发挥自己的创造力,做出各种神奇的动画效果,ok,就到这里!

源码点击下载

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