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); } }