viewpager切换的动画效果

实现ViewPager的切换的动画效果

①http://blog.csdn.net/lmj623565791/article/details/40411921/

②http://blog.csdn.net/lmj623565791/article/details/38026503 

目录 

1. 用官方给的两个切换动画效果，看看效果
2. 分析为为什么android 3.0的版本不能使用
3. 详细的分析ViewPager的实现动画，然后自己定义

1.ViewPager的动画的效果，应用Google提供的两个例子实现

   ①在XML中添加ViewPager的控件

   

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

  ②在java代码中调用设置动画的方法

        //第一个参数true child倒叙 false child顺序
        //第二个参数就是实现ViewPager.PageTransformer的接口的类
        mViewPager.setPageTransformer(arg0, arg1);

  两种实现pagertransformer接口的类

 <1>DepthPageTransformer

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

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);
        }
    }
}

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

<2>ZoomOutPageTransformer

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

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

    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);
        }
    }
}

2.但是只能在android3.0或者以前才有效，具体的ViewPager的源码，中的方法

/**
     * Set a {@link PageTransformer} that will be called for each attached page whenever
     * the scroll position is changed. This allows the application to apply custom property
     * transformations to each page, overriding the default sliding look and feel.
     *
     * <p><em>Note:</em> Prior to Android 3.0 the property animation APIs did not exist.
     * As a result, setting a PageTransformer prior to Android 3.0 (API 11) will have no effect.</p>
     *
     * @param reverseDrawingOrder true if the supplied PageTransformer requires page views
     *                            to be drawn from last to first instead of first to last.
     * @param transformer PageTransformer that will modify each page's animation properties
     */
    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();
        }
    }

主要是由于android3.0上采用的属性动画，所以这里进行了判断，通过上面的代码可以看见在实现ViewPager.setPagerTransformer()方法的时候，先进行判断，当前的Api的版本。如果<11执行这个方法就没有效，

 3.实现自己的ViewPager的切换动画

  

/**
 * 实现自定义切换动画
 * @author kc
 *
 */
public class MyPageTransformer implements ViewPager.PageTransformer {

    public void transformPage(View view, float position) {
        // 通过打印log的方式
        // 当A页切换到B页的时候
        // A页的position是从0 ~ -1的变化
        // B页的position是从1 ~ 0.0的变化
        if (position < -1) { // [-Infinity,-1) 这时的view是看不见的
            // TODO
        } else if (position <= 0) { // [-1,0] A页
            // TODO
        } else if (position <= 1) { // (0,1]  B页
            // TODO
        } else { // (1,+Infinity] 这时的view是看不见的
            // TODO
        }
    }

}