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();  } }}