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();
}
}
}