public class PageDragView extends ViewGroup{
private static final String TAG = PageDragView.class.getSimpleName();
/**
* 用来追踪触摸事件(flinging事件和其他手势事件)的速率
* 用obtain()函数来获得类的实例,
* 用addMovement(MotionEvent)函数将motion event加入到VelocityTracker类实例中,
* 当你使用到速率时,使用computeCurrentVelocity(int)初始化速率的单位,
* 并获得当前的事件的速率,
* 然后使用getXVelocity() 或getXVelocity()获得横向和竖向的速率
*/
private VelocityTracker mVelocityTracker;
private static final int SNAP_VELOCITY = 600;
//滚动事件
private Scroller mScroller;
private int mCurScreen;
private int mDefaultScreen = 0;
//临时存储Motion的X坐标
private float mLastMotionX;
private OnViewChangeListener mOnViewChangeListener;//监听事件
public PageDragView(Context context) {
super(context);
init(context);
}
public PageDragView(Context context, AttributeSet attrs) {
super(context, attrs);
init(context);
}
public PageDragView(Context context, AttributeSet attrs, int defStyle) {
super(context, attrs, defStyle);
init(context);
}
private void init(Context context){
mCurScreen = mDefaultScreen;
mScroller = new Scroller(context);
}
/**onMeasure->onLayout*/
@Override
protected void onLayout(boolean changed, int l, int t, int r, int b) {
// TODO Auto-generated method stub
Log.i(TAG, "changed= " + changed);
if (changed) {
int childLeft = 0;
final int childCount = getChildCount();
for (int i=0; i<childCount; i++) {
final View childView = getChildAt(i);
if (childView.getVisibility() != View.GONE) {
Log.i(TAG, "childLeft= " + childLeft);
final int childWidth = childView.getMeasuredWidth();
childView.layout(childLeft, 0,
childLeft+childWidth, childView.getMeasuredHeight());
childLeft += childWidth;
}
}
}
}
@Override
protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
// TODO Auto-generated method stub
super.onMeasure(widthMeasureSpec, heightMeasureSpec);
final int width = MeasureSpec.getSize(widthMeasureSpec);
final int widthMode = MeasureSpec.getMode(widthMeasureSpec);
Log.i(TAG, "widthMeasureSpec= " + widthMeasureSpec);
Log.i(TAG, "heightMeasureSpec= " + heightMeasureSpec);
final int count = getChildCount();
for (int i = 0; i < count; i++) {
getChildAt(i).measure(widthMeasureSpec, heightMeasureSpec);
}
scrollTo(mCurScreen * width, 0);
}
//滚动操作
public void snapToScreen(int whichScreen) {
whichScreen = Math.max(0, Math.min(whichScreen, getChildCount()-1));
if (getScrollX() != (whichScreen*getWidth())) {
final int delta = whichScreen*getWidth()-getScrollX();
mScroller.startScroll(getScrollX(), 0,delta, 0, Math.abs(delta)*2);
mCurScreen = whichScreen;
invalidate(); // Redraw the layout
if (mOnViewChangeListener != null)
{
mOnViewChangeListener.OnViewChange(mCurScreen);
}
}
}
public void snapToDestination() {
final int screenWidth = getWidth();
final int destScreen = (getScrollX()+ screenWidth/2)/screenWidth;
snapToScreen(destScreen);
}
@Override
public void computeScroll() {
// TODO Auto-generated method stub
if (mScroller.computeScrollOffset()) {
scrollTo(mScroller.getCurrX(), mScroller.getCurrY());
postInvalidate();
}
}
//View的触屏事件
@Override
public boolean onTouchEvent(MotionEvent event) {
// TODO Auto-generated method stub
final int action = event.getAction();
final float x = event.getX();
final float y = event.getY();
switch (action) {
case MotionEvent.ACTION_DOWN:
if (mVelocityTracker == null) {
mVelocityTracker = VelocityTracker.obtain();
mVelocityTracker.addMovement(event);
}
if(!mScroller.isFinished()){
mScroller.abortAnimation();
}
mLastMotionX = x;
Log.i(TAG, "mLastMotionX= " + mLastMotionX);
break;
case MotionEvent.ACTION_MOVE:
//滑动的距离
int deltaX = (int)(mLastMotionX - x);
if (IsCanMove(deltaX)){
if (mVelocityTracker != null){
mVelocityTracker.addMovement(event);
}
mLastMotionX = x;
//在当前位置,继续偏移(x,y)个单位
scrollBy(deltaX, 0);
}
break;
case MotionEvent.ACTION_UP:
int velocityX = 0;
if (mVelocityTracker != null){
mVelocityTracker.addMovement(event);
mVelocityTracker.computeCurrentVelocity(1000);
//X方向滑动的速率
velocityX = (int) mVelocityTracker.getXVelocity();
}
Log.i(TAG, "velocityX= " + velocityX);
/**mCurScreen 当前屏幕的下标值*/
if (velocityX > SNAP_VELOCITY && mCurScreen > 0) {
snapToScreen(mCurScreen - 1);
} else if (velocityX < -SNAP_VELOCITY
&& mCurScreen < getChildCount() - 1) {
snapToScreen(mCurScreen + 1);
} else {
snapToDestination();
}
if (mVelocityTracker != null) {
mVelocityTracker.recycle();
mVelocityTracker = null;
}
break;
}
return true;
}
private boolean IsCanMove(int deltaX){
//getScrollX() 视图起始坐标偏移值
if(getScrollX() <= 0 && deltaX < 0 ){
return false;
}
if(getScrollX() >= (getChildCount() - 1) * getWidth() && deltaX > 0){
return false;
}
return true;
}
public void SetOnViewChangeListener(OnViewChangeListener listener){
mOnViewChangeListener = listener;
}
public interface OnViewChangeListener {
/**监听事件
* @params view 当前的View
* @return
*/
public void OnViewChange(int view);
}
}