ViewPager切换动画PageTransformer的使用

来源：互联网发布：上海unity3d培训机构编辑：程序博客网时间：2024/06/11 09:37

Android从3.0开始添加了属性动画后，诸多难以实现的动画都可以轻松解决了，v4包下的ViewPager控件当然也不例外，相对于非常平庸的默认切换动画，Google官方给我们展示了两个动画例子：DepthPageTransformer和ZoomOutPageTransformer，比较炫。

实际上我们也可以通过实现ViewPager.PageTransformer接口来做出完全不同的切换动画效果。实现PageTransformer接口就只要实现一个方法：transformPage(View view,float position);该方法的两个参数尤为重要，理解它是我们自定义ViewPager动画的重点。

transformPage(View view,float position);

第一个参数view顾名思义就是我们需要滑动的那个View。
第二个参数position，这个float类型的参数并不是我们平常所理解的位置，而是表示滑动的View的一种状态，比如：当滑动到正全屏时，position是0，而向左滑动，使得右边刚好有一部被进入屏幕时，position是1，如果前一页和下一页基本各在屏幕占一半时，前一页的position是-0.5，后一页的posiotn是0.5，所以根据position的值我们就可以自行设置需要的alpha，ScaleX/Y,translationX/Y等参数值。

下面，我们就来看看Google官方提供的两种动画效果的源码及对应的动画，理解了原理自定义动画可以仿照源码了：

DepthPageTransformer:

import android.annotation.SuppressLint;import android.support.v4.view.ViewPager.PageTransformer;import android.view.View;public class DepthPageTransformer implements PageTransformer {    private static float MIN_SCALE = 0.75f;    @SuppressLint("NewApi")    @Override    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);        }    }}

效果为：

ZoomOutPageTransformer：

import android.support.v4.view.ViewPager.PageTransformer;import android.view.View;public class ZoomOutPageTransformer implements PageTransformer {    private static float MIN_SCALE = 0.85f;    private static float MIN_ALPHA = 0.5f;    @Override    public void transformPage(View view, float position) {        int pageWidth = view.getWidth();        int pageHeight = view.getHeight();        if (position < -1) { // [-Infinity,-1)            // This page is way off-screen to the left.            view.setAlpha(0);        } else if (position <= 1) { // [-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);        }    }}

效果为：

下面我们来看看怎么使用ViewPager，让它加入动画。

其实就是通过mViewPager.setPageTransformer(true, new DepthPageTransformer());来设置。

布局：

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

代码：

public class MainActivity extends ActionBarActivity {    private int[] imageId = new int[]{R.mipmap.bg,R.mipmap.one, R.mipmap.two, R.mipmap.three};    @Override    protected void onCreate(Bundle savedInstanceState) {        super.onCreate(savedInstanceState);        setContentView(R.layout.activity_main);        ViewPager mViewPager = (ViewPager) findViewById(R.id.viewpager);        mViewPager.setAdapter(new ViewPagerAdapter(this,imageId));//      mViewPager.setPageTransformer(true, new ZoomOutPageTransformer());        mViewPager.setPageTransformer(true,new DepthPageTransformer());    }    class ViewPagerAdapter extends PagerAdapter {        private ArrayList<ImageView> mImages ;        private int[] imagesId;        private Context context;        public ViewPagerAdapter(Context context,int[] resourceId){            this.context = context;            this.imagesId = resourceId;            mImages = new ArrayList<>();        }        @Override        public Object instantiateItem(ViewGroup container, int position) {            ImageView imageView = new ImageView(context);            imageView.setImageResource(imagesId[position]);            imageView.setScaleType(ImageView.ScaleType.CENTER_CROP);            container.addView(imageView);            mImages.add(imageView);            return imageView;        }        @Override        public void destroyItem(ViewGroup container, int position, Object object) {//            super.destroyItem(container, position, object);//这行要去除，否则会报错            container.removeView(mImages.get(position));        }        @Override        public int getCount() {            return imagesId.length;        }        @Override        public boolean isViewFromObject(View view, Object object) {            return view==object;        }    }}

另外说明一点：

关于ViewPager的适配器，有两种实现：

直接继承PagerAdapter，即：

class ViewPagerAdapter extends PagerAdapter {        private ArrayList<ImageView> mImages ;        private int[] imagesId;        private Context context;        public ViewPagerAdapter(Context context,int[] resourceId){            this.context = context;            this.imagesId = resourceId;            mImages = new ArrayList<>();        }        @Override        public Object instantiateItem(ViewGroup container, int position) {            ImageView imageView = new ImageView(context);            imageView.setImageResource(imagesId[position]);            imageView.setScaleType(ImageView.ScaleType.CENTER_CROP);            container.addView(imageView);            mImages.add(imageView);            return imageView;        }        @Override        public void destroyItem(ViewGroup container, int position, Object object) {//            super.destroyItem(container, position, object);//这行要去除，否则会报错            container.removeView(mImages.get(position));        }        @Override        public int getCount() {            return imagesId.length;        }        @Override        public boolean isViewFromObject(View view, Object object) {            return view==object;        }

继承至FragmentPagerAdapter：即

class FragmentViewPagerAdapter extends FragmentPagerAdapter{        private final List<Fragment> mFragments = new ArrayList<>();//添加的Fragment的集合        public FragmentViewPagerAdapter(FragmentManager fm) {            super(fm);        }        public void addFragment(Fragment fragment) {            mFragments.add(fragment);        }        @Override        public Fragment getItem(int position) {            //得到对应position的Fragment            return mFragments.get(position);        }        @Override        public int getCount() {            //返回Fragment的数量            return mFragments.size();        }    }

好了，就说到这了。。。

源码地址：http://download.csdn.net/detail/u010687392/8913511

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