Android Custom View Elastic Scroller Detailed Explanation

 //① Example of a Scroller, it has three constructs as follows  //public Scroller (Context context)
  //public Scroller (Context context, Interpolator interpolator)//Pass in a time interpolator  //public Scroller (Context context, Interpolator interpolator, boolean flywheel)
  Scroller mScroller=new Scroller(context);

  //②Use Scroller  //startScroll() passes in some parameters: start position, end position, start time slide to end position.  (int startX,int startY,int endx,int endY,int duration);
  invalidate();//In ViewGroup, the invalidate() method will cause the execution of the computeScroll() method
  //③ In the computeScroll() method, determine whether mScroller is ending. If it does not end, call scrollTo() to put the view in the correct position.  @Override
  public void computeScroll() {
   //computeScrollOffset() determines whether it is still scrolling. If it is still scrolling, it will get the position where the view should be at a certain moment, refresh the values ​​of mCurrX and mCurrY in the Scroller, and return true;   if (()) {
    scrollTo((), ());
    //Update the interface    postInvalidate();
   }
   ();
  }

package ;

/**
  * Scroller practice, a simple ViewPager
  * @author : liujian
  * @since : 2017/12/17
  */

public class ScrollLayout extends ViewGroup {
 private Scroller mScroller;
 //The minimum distance of the current device sliding private int mTouchSlop;

 private int leftBorder;//The left boundary of the layout content private int rightBorder;//The right boundary of the layout content
 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 = (getContext()).getScaledTouchSlop();
  mScroller = new Scroller(getContext());
 }

 @Override
 protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
  (widthMeasureSpec, heightMeasureSpec);
  // Give a recommended measurement size and measurement mode for a subView in ScrollLayout  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);
   (i * (), 0, (i + 1) * (), ());
  }
  leftBorder = getChildAt(0).getLeft();
  rightBorder = getChildAt(getChildCount() - 1).getRight();
 }

 @Override
 public boolean onInterceptTouchEvent(MotionEvent ev) {
  switch (()) {
   case MotionEvent.ACTION_DOWN:
    mRawXDown = ();
    mRawXLastMove = mRawXDown;
    break;
   case MotionEvent.ACTION_MOVE:
    mRawXMove = ();
    mRawXLastMove = mRawXMove;
    float distance = (mRawXMove - mRawXDown);
    //When sliding left and right, intercepting the touch event of the subview    if (distance > mTouchSlop) {
     return true;
    }
    break;
   case MotionEvent.ACTION_UP:
    break;
  }
  return (ev);
 }

 @SuppressLint("ClickableViewAccessibility")
 @Override
 public boolean onTouchEvent(MotionEvent event) {
  switch (()) {
   case MotionEvent.ACTION_MOVE:
    mRawXMove = ();
    int distanceX = (int) (mRawXLastMove - mRawXMove);
    //Treatment of boundary exceptions    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:
    //The current page    int targetIndex = (getScrollX() + getWidth() / 2) / getWidth();
    int dx = targetIndex * getWidth() - getScrollX();
    ("TAG", "dx: " + dx);
    ("TAG", "getScrollX: " + getScrollX());
    ("TAG", "getWidth: " + getWidth());

    // The second step is to call the startScroll() method to initialize the rolling data and refresh the interface    (getScrollX(), 0, dx, 0);
    invalidate();
    break;
  }
  return (event);
 }

 @Override
 public void computeScroll() {
  if (()) {
   scrollTo((), ());
   invalidate();
  }
 }
}