Android继承ViewGroup实现Scroll滑动效果的方法示例

public class MyScrollLayout extends ViewGroup{
 private int curScreen;
 private int defaultScreen = 0;
 private Scroller mScroller;
 private float mLastMotionX = 0;
 private VelocityTracker mVelocityTracker;

 public MyScrollLayout(Context context, AttributeSet attrs, int defStyleAttr) {
  super(context, attrs, defStyleAttr);
  init(context);
 }
 public MyScrollLayout(Context context, AttributeSet attrs) {
  super(context, attrs);
  init(context);
 }
 public MyScrollLayout(Context context) {
  super(context);
  init(context);
 }
 private void init(Context context){
  curScreen = defaultScreen;
  mScroller = new Scroller(context);
 }
 @Override
 public void computeScroll() {
  if(mScroller.computeScrollOffset()){
   scrollTo(mScroller.getCurrX(), mScroller.getCurrY());
   postInvalidate();
  }
 }
 @Override
 public boolean onTouchEvent(MotionEvent event) {
  // TODO Auto-generated method stub
  int action = event.getAction();
  float x = event.getX();
  switch (action) {
  case MotionEvent.ACTION_DOWN:
   if(mVelocityTracker==null){
    mVelocityTracker = VelocityTracker.obtain();
    mVelocityTracker.addMovement(event);
   }
   if(!mScroller.isFinished()){
    mScroller.abortAnimation();
   }
   mLastMotionX = event.getX();
   break;
  case MotionEvent.ACTION_MOVE:
   float delt = mLastMotionX-x;
   if(isCanMove((int)delt)){
   if(mVelocityTracker!=null){
    mVelocityTracker.addMovement(event);
   }
   mLastMotionX = x;
   scrollBy((int)delt, 0);
   }
   break;
  case MotionEvent.ACTION_UP:
   if(mVelocityTracker!=null){
    mVelocityTracker.addMovement(event);
    mVelocityTracker.computeCurrentVelocity(1000);
    float pxsec = mVelocityTracker.getXVelocity();
    if(pxsec>600 && curScreen >0){
     snapToScreen(curScreen-1);
    }else if(pxsec<-600 && curScreen<getChildCount()-1){
     snapToScreen(curScreen+1);
    }else{
     //主要是用来获取该滑动到哪个界面，最终调用的是invalid调用draw方法然后draw调用computeScroll方法，然后使用scroller对象
     snapToDestination();
    }
    mVelocityTracker.recycle();
    mVelocityTracker = null;
   }
   break;
  default:
   break;
  }
  return true;
 }
 private void snapToScreen(int screen){
  int whichscreen = Math.max(0, Math.min(screen, getChildCount()-1));
  if(getScrollX()!=(whichscreen*getWidth())){
   final int delat = whichscreen*getWidth() - getScrollX();
   mScroller.startScroll(getScrollX(), 0, delat, 0, Math.abs(delat)*2);
   curScreen = whichscreen;
   invalidate();
  }
 }
 private void snapToDestination(){
  int screen = (getScrollX()+getWidth()/2)/getWidth();
  snapToScreen(screen);
 }
 private boolean isCanMove(int delat){
  /*if(getScrollX()<0 && delat<0){
   return false;
  }*/
  if(getScrollX()>=(getChildCount()-1)*getWidth() && delat>0){
   return false;
  }
  return true;
 }
 @Override
 protected void onLayout(boolean changed, int l, int t, int r, int b) {
  if(changed){
  int totalHeight = 0;
  int totalwidth = 0;
  int childCount = getChildCount();
  for(int i=0; i<childCount; i++){
   View childView = getChildAt(i);
   int childwidth = childView.getMeasuredWidth();
   int childheight = childView.getMeasuredHeight();
   childView.layout(totalwidth, t, totalwidth+childwidth, b);
   totalHeight += childheight;
   totalwidth += childwidth;
  }
  }
 }
 @Override
 protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
  // TODO Auto-generated method stub
  measureChildren(widthMeasureSpec, heightMeasureSpec);
  super.onMeasure(widthMeasureSpec, heightMeasureSpec);
 }
}

Scroller.startScroll(getScrollX(), 0, delat, 0, Math.abs(delat)*2);