【iOS开发系列】scrollView中的directionalLockEnabled

scrollView中的directionalLockEnabled的功能本来就是用来让用户每次只在一个方向上滚动，竖直或者水平，但是如果初始移动方向处于45°左右的时候，这个锁就失效了。

苹果官方发现了这个问题，在官方文档里有如下描述，但是没有解决：

"If this property is NO, scrolling is permitted in both horizontal and vertical directions. If this property is YES and the user begins dragging in one general direction (horizontally or vertically), the scroll view disables scrolling in the other direction. If the drag direction is diagonal, then scrolling will not be locked and the user can drag in any direction until the drag completes. The default value is NO"

这是stackoverflow上的讨论：http://stackoverflow.com/questions/728014/uiscrollview-paging-horizontally-scrolling-vertically 

@property (nonatomic) CGPoint scrollViewStartPosPoint;@property (nonatomic) int     scrollDirection;@synthesize scrollViewStartPosPoint = _scrollViewStartPosPoint;@synthesize scrollDirection = _scrollDirection;- (id)initWithFrame:(CGRect)frame{     _scrollDirection = 0;}- (void)scrollViewDidScroll:(UIScrollView *)scrollView {     if (self.scrollDirection == 0){//we need to determine direction        //use the difference between positions to determine the direction.        if (abs(self.scrollViewStartPosPoint.x-scrollView.contentOffset.x)<            abs(self.scrollViewStartPosPoint.y-scrollView.contentOffset.y)){            //Vertical Scrolling            self.scrollDirection = 1;        } else {            //Horitonzal Scrolling            self.scrollDirection = 2;        }    }    //Update scroll position of the scrollview according to detected direction.    if (self.scrollDirection == 1) {        scrollView.contentOffset = CGPointMake(self.scrollViewStartPosPoint.x,scrollView.contentOffset.y);    } else if (self.scrollDirection == 2){        scrollView.contentOffset = CGPointMake(scrollView.contentOffset.x,self.scrollViewStartPosPoint.y);    }}- (void)scrollViewWillBeginDragging:(UIScrollView *)scrollView {    self.scrollViewStartPosPoint = scrollView.contentOffset;    self.scrollDirection = 0;}- (void)scrollViewDidEndDragging:(UIScrollView *)scrollView willDecelerate:(BOOL)decelerate {    if (decelerate) {        self.scrollDirection =0;    }}- (void)scrollViewDidEndDecelerating:(UIScrollView *)scrollView {    self.scrollDirection =0;}- (void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event {    [super touchesBegan:touches withEvent:event]; // always forward touchesBegan -- there's no way to forward it later//    if (_isHorizontalScroll)//        return; // UIScrollView is in charge now//    if ([touches count] == [[event touchesForView:self] count]) { // initial touch//        _originalPoint = [[touches anyObject] locationInView:self];//        _currentChild = [self honestHitTest:_originalPoint withEvent:event];//        _isMultitouch = NO;//    }//    _isMultitouch |= ([[event touchesForView:self] count] > 1);//    [_currentChild touchesBegan:touches withEvent:event];}- (void)touchesMoved:(NSSet *)touches withEvent:(UIEvent *)event {     [super touchesMoved:touches withEvent:event];//    if (!_isHorizontalScroll && !_isMultitouch) {//        CGPoint point = [[touches anyObject] locationInView:self];//        if (fabsf(_originalPoint.x - point.x) > kThresholdX && fabsf(_originalPoint.y - point.y) < kThresholdY) {//            _isHorizontalScroll = YES;//            [_currentChild touchesCancelled:[event touchesForView:self] withEvent:event]//        }//    }//    if (_isHorizontalScroll)//        [super touchesMoved:touches withEvent:event]; // UIScrollView only kicks in on horizontal scroll//    else//        [_currentChild touchesMoved:touches withEvent:event];}