UISiew裏面的UIScrollView問題

Question

如果我有一個UIView作爲UIScrollView的子視圖，並且這個滾動視圖是一個水平滾動視圖，我怎麼知道UIView（子視圖）何時不在UIScrollView中，以便我可以刪除它作爲子視圖並將其存儲在其他地方以供重用？有這樣的代表嗎？

Answer 1

是的，這是一個委託，你需要使用UIScrollViewDelegate。

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

的方法scrollViewDidScroll告訴你，當滾動追加，所以在這個功能，你可以測試contentOffset財產（scrollview.contentOffset.x），然後將它與您的視圖的位置和大小比較（myView.frame.origin.x + myView.frame.size.width）。

所以basicaly你應該做的

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

如果你只有2次顯示，只是想重新使用每個視圖中，你可以找到當前顯示的是這樣的觀點：

//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 
    } 

之後，您需要向nextView添加一些內容，將其添加到滾動視圖並在隱藏時刪除currentView。

Answer 2

您可以使用UIScrollViewDelegate方法scrollViewDidEndDecelerating:和一些自定義代碼來實現此目的。

- (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 
    } 
}