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);