UISiew里面的UIScrollView问题

Question

如果我有一个UIView作为UIScrollView的子视图，并且这个滚动视图是一个水平滚动视图，我怎么知道UIView（子视图）何时不在UIScrollView中，以便我可以删除它作为子视图并将其存储在其他地方以供重用？有这样的代表吗？

Answer 1

是的，这是一个委托，你需要使用UIScrollViewDelegate。

http://developer.apple.com/library/IOS/#documentation/UIKit/Reference/UIScrollViewDelegate_Protocol/Reference/UIScrollViewDelegate.html

的方法scrollViewDidScroll告诉你，当滚动追加，所以在这个功能，你可以测试contentOffset财产（scrollview.contentOffset.x），然后将它与您的视图的位置和大小比较（myView.frame.origin.x + myView.frame.size.width）。

所以basicaly你应该做的

if(scrollview.contentOffset.x > (myView.frame.origin.x + myView.frame.size.width)) 
//Remove my view to reuse it 

如果你只有2次显示，只是想重新使用每个视图中，你可以找到当前显示的是这样的观点：

//Assuming your views had the same width and it is store in the pageWidth variable 
    float currPosition = photoGalleryScrollView.contentOffset.x; 
    //We look for the selected page by comparing his width with the current scroll view position 
    int selectedPage = roundf(currPosition/pageWidth); 
    float truePosition = selectedPage * pageWidth; 
    int zone = selectedPage % 2; 
    BOOL view1Active = zone == 0; 
    UIView *nextView = view1Active ? view2 : view1; 
    UIView *currentView = view1Active ? view1 : view2; 

    //We search after the next page 
    int nextpage = truePosition > currPos + 1 ? selectedPage-1 : selectedPage+1; 

    //then we compare our next page with the selectd page 
    if(nextpage > selectedPage){ 
     //show next view 
    } 
    else{ 
     //show previous view 
    } 

之后，您需要向nextView添加一些内容，将其添加到滚动视图并在隐藏时删除currentView。

Answer 2

您可以使用UIScrollViewDelegate方法scrollViewDidEndDecelerating:和一些自定义代码来实现此目的。

- (void)viewDidLoad { 
    [super viewDidLoad]; 
    //set theScrollView's delegate 
    theScrollView.delegate = self; 
} 

//custom method for determining visible rect of scrollView 
- (CGRect)visibleRectForScrollView:(UIScrollView *)scrollView; { 
    CGFloat scale = (CGFloat) 1.0/scrollView.zoomScale; 
    CGRect visibleRect; 
    visibleRect.origin = scrollView.contentOffset; 
    visibleRect.size = scrollView.bounds.size; 
    float theScale = 1.0/scale; 
    visibleRect.origin.x *= theScale; 
    visibleRect.origin.y *= theScale; 
    visibleRect.size.width *= theScale; 
    visibleRect.size.height *= theScale; 
    return visibleRect; 
} 

//UIScrollView Delegate method 
- (void)scrollViewDidEndDecelerating:(UIScrollView *)scrollView { 
    BOOL viewVisisble = CGRectContainsRect([self visisbleRectForScrollView:theScrollView], theView.frame); 
    if(!viewVisisble) { 
     //do something 
    } 
}