viewWillAppear的子视图

Question

我有UIScrollView与多个UIVIew子视图。我想更新每个UIView显示在UIScrollView可见部分的数据。

什么是被触发的回调？我试图viewWillAppear，但它似乎并没有被调用。

谢谢。 :)

Answer 1

你必须自己做计算。在滚动视图的委托实施scrollViewDidScroll:和手动计算，其观点是可见的（例如，通过检查，如果CGRectIntersectsRect(scrollView.bounds, subview.frame)返回true

Answer 2

轻微的改进，我想知道这是显示在滚动视图的视图的数量：。

- (void)scrollViewDidScroll:(UIScrollView *)scrollView; 
{ 
    // Figure out how much of the self.userFeedbackView is displayed. 
    CGRect frame = CGRectIntersection(self.scrollView.bounds, self.userFeedbackView.frame); 
    CGFloat proportion = (frame.size.height*frame.size.width)/(self.userFeedbackView.frameWidth*self.userFeedbackView.frameHeight); 
    NSLog(@"%f; %@", proportion, NSStringFromCGRect(frame)); 
} 

Answer 3

以上的答案是正确的，如果你的滚动视图是不是在状态的放大。在情况下，如果你需要考虑变焦太

这里是代码

您的滚动视图可以放大上述计算将无法正常工作

CGRect visibleRect; 
       visibleRect.origin = self.mapScrollView.contentOffset; 
       visibleRect.size = self.mapScrollView.bounds.size; 

       float theScale = 1.0/self.mapScrollView.zoomScale; 
       visibleRect.origin.x *= theScale; 
       visibleRect.origin.y *= theScale; 
       visibleRect.size.width *= theScale; 
       visibleRect.size.height *= theScale; 
       if(CGRectIntersectsRect(visibleRect, btnPin.frame)){ 
         ... 
       } 

Answer 4

斯威夫特3溶液

func scrollViewDidScroll(_ scrollView: UIScrollView) { 
    let viewFrame = greenView.frame 

    let container = CGRect(x: scrollView.contentOffset.x, y: scrollView.contentOffset.y, width: scrollView.frame.size.width, height: scrollView.frame.size.height) 


    // We may have received messages while this tableview is offscreen 
    if (viewFrame.intersects(container)) { 
     // Do work here 
     print("view is visible") 
    } 
    else{ 
     print("nope view is not on the screen") 
    } 
}