如何判断UIView是否在屏幕上可见?

我还没试过。但是 CGRectIntersectsRect() , -[UIView convertRect:to(from)View] 和 -[UIScrollView contentOffset]

for(UIView* view in scrollView.subviews) {
    if([view isKindOfClass:[SomeView class]]) {

        // the parent of view of scrollView (which basically matches the application frame)
        CGRect f = self.view.frame; 
        // adjust our frame to match the scroll view's content offset
        f.origin.y = _scrollView.contentOffset.y;

        CGRect r = [self.view convertRect:view.frame toView:self.view];

        if(CGRectIntersectsRect(f, r)) {
            // view is visible
        }
    }
}

如果您主要担心释放不在视图层次结构中的对象,可以测试它是否具有superview,如中所示:

if (myView.superview){
 //do something with myView because you can assume it is on the screen
}
else {
 //myView is not in the view hierarchy
}

CGRect viewFrame = self.view.frame;
CGRect appFrame = [[UIScreen mainScreen] applicationFrame];

// We may have received messages while this tableview is offscreen
if (CGRectIntersectsRect(viewFrame, appFrame)) {
    // Do work here
}