使用反射机制修改viewPager切换滑动速度

ViewPager的惯性效果（滑到一定距离自动平滑到另一个pager，或者调用setCurrentItem）是通过scroller来实现的， 其中有个变量为mScroller，为了修改这个滑动的速度，需要改变mScroller的一些值，但是mScroller是私有变量，所以在不直接修改ViewPager源码的情况下，只能用反射修改mScroller。

自定义一个Scroller

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public class FixedSpeedScroller extends Scroller {     private int mDuration = 1500;                                                                                                                  public FixedSpeedScroller(Context context) {         super(context);     }                                                                                                                  public FixedSpeedScroller(Context context, Interpolator interpolator) {         super(context, interpolator);     }                                                                                                                  @Override     public void startScroll(int startX, int startY, int dx, int dy, int duration) {         // Ignore received duration, use fixed one instead         super.startScroll(startX, startY, dx, dy, mDuration);     }                                                                                                                  @Override     public void startScroll(int startX, int startY, int dx, int dy) {         // Ignore received duration, use fixed one instead         super.startScroll(startX, startY, dx, dy, mDuration);     }                                                                                                                  public void setmDuration(int time) {         mDuration = time;     }                                                                                                                  public int getmDuration() {         return mDuration;     } }

使用方法：

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try {                 Field field = ViewPager.class.getDeclaredField("mScroller");                 field.setAccessible(true);                 FixedSpeedScroller scroller = new FixedSpeedScroller(mViewPager.getContext(),                         new AccelerateInterpolator());                 field.set(mViewPager, scroller);                 scroller.setmDuration(2000);             } catch (Exception e) {                 LogUtils.e(TAG, "", e);             }

注意点：
PagerAdapter 的destroyItem 每次会删除上一个页面，导致，如果做自动切换页面时会看不到动画.

解决办法:
destoryItem中不做删除view，instantiateItem中对view是否有parent做为判断条件，这种情况适用于，少量的固定的子View，比如一个Banner，banner中做自动循环播放