Android自定义View弹性滑动Scroller详解

 //①实例一个Scroller,它有三个构造方法如下
  //public Scroller (Context context)
  //public Scroller (Context context, Interpolator interpolator)//传入一个时间插值器
  //public Scroller (Context context, Interpolator interpolator, boolean flywheel)
  Scroller mScroller=new Scroller(context);

  //②使用Scroller
  //startScroll()传入一些参数：开始位置，结束位置，开始时间滑动到结束位置的完成时间。
  mScrooler.startScroll(int startX,int startY,int endx,int endY,int duration);
  invalidate();//在ViewGroup中,invalidate()方法会导致computeScroll()方法的执行

  //③在computeScroll()的方法中判断：mScroller是否结束，如果没有结束就调用scrollTo()让view处于正确的位置
  @Override
  public void computeScroll() {
   //computeScrollOffset()判断是否还在滚动，如果还在滚动,会获取到某一时刻view应该所在的位置，刷新Scroller中mCurrX，mCurrY的值，并且return true;
   if (mScroller.computeScrollOffset()) {
    scrollTo(mScroller.getCurrX(), mScroller.getCurrY());
    //更新界面
    postInvalidate();
   }
   super.computeScroll();
  }

package com.liujian.chart;

/**
 * Scroller练习，一个简单的ViewPager
 * @author : liujian
 * @since : 2017/12/17
 */

public class ScrollLayout extends ViewGroup {
 private Scroller mScroller;
 //当前设备滑动的最小距离
 private int mTouchSlop;

 private int leftBorder;//布局内容的左边界
 private int rightBorder;//布局内容的右边界

 private float mRawXDown;
 private float mRawXMove;
 private float mRawXLastMove;

 public ScrollLayout(Context context) {
  super(context);
  initView(context);
 }

 public ScrollLayout(Context context, @Nullable AttributeSet attrs) {
  super(context, attrs);
  initView(context);
 }

 public ScrollLayout(Context context, @Nullable AttributeSet attrs, int defStyleAttr) {
  super(context, attrs, defStyleAttr);
  initView(context);
 }

 private void initView(Context context) {
  mTouchSlop = ViewConfiguration.get(getContext()).getScaledTouchSlop();
  mScroller = new Scroller(getContext());
 }

 @Override
 protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
  super.onMeasure(widthMeasureSpec, heightMeasureSpec);
  //为ScrollLayout中的某一个子View给出一个建议的测量大小和测量模式
  measureChildren(widthMeasureSpec, heightMeasureSpec);
 }

 @Override
 protected void onLayout(boolean changed, int l, int t, int r, int b) {
  int childCount = getChildCount();
  for (int i = 0; i < childCount; i++) {
   View view = getChildAt(i);
   view.layout(i * view.getMeasuredWidth(), 0, (i + 1) * view.getMeasuredWidth(), view.getMeasuredHeight());
  }
  leftBorder = getChildAt(0).getLeft();
  rightBorder = getChildAt(getChildCount() - 1).getRight();
 }

 @Override
 public boolean onInterceptTouchEvent(MotionEvent ev) {
  switch (ev.getAction()) {
   case MotionEvent.ACTION_DOWN:
    mRawXDown = ev.getRawX();
    mRawXLastMove = mRawXDown;
    break;
   case MotionEvent.ACTION_MOVE:
    mRawXMove = ev.getRawX();
    mRawXLastMove = mRawXMove;
    float distance = Math.abs(mRawXMove - mRawXDown);
    //左右滑动时，拦截子view的触摸事件
    if (distance > mTouchSlop) {
     return true;
    }
    break;
   case MotionEvent.ACTION_UP:
    break;
  }
  return super.onInterceptTouchEvent(ev);
 }

 @SuppressLint("ClickableViewAccessibility")
 @Override
 public boolean onTouchEvent(MotionEvent event) {
  switch (event.getAction()) {
   case MotionEvent.ACTION_MOVE:
    mRawXMove = event.getRawX();
    int distanceX = (int) (mRawXLastMove - mRawXMove);
    //对边界异常情况的处理
    if (getScrollX() + distanceX < leftBorder) {
     scrollBy(leftBorder, 0);
    }
    if (getScrollX() + getWidth() + distanceX > rightBorder) {
     scrollBy(rightBorder - getWidth(), 0);
    }
    scrollBy(distanceX, 0);
    mRawXLastMove = mRawXMove;
    break;
   case MotionEvent.ACTION_UP:
    //当前所在的page页面
    int targetIndex = (getScrollX() + getWidth() / 2) / getWidth();
    int dx = targetIndex * getWidth() - getScrollX();
    Log.i("TAG", "dx: " + dx);
    Log.i("TAG", "getScrollX: " + getScrollX());
    Log.i("TAG", "getWidth: " + getWidth());

    // 第二步，调用startScroll()方法来初始化滚动数据并刷新界面
    mScroller.startScroll(getScrollX(), 0, dx, 0);
    invalidate();
    break;
  }
  return super.onTouchEvent(event);
 }

 @Override
 public void computeScroll() {
  if (mScroller.computeScrollOffset()) {
   scrollTo(mScroller.getCurrX(), mScroller.getCurrY());
   invalidate();
  }
 }
}