Summary of scrollsToTop problem in IOS

scrollsToTop summary:

UIScrollView is a class used to display scrolling. He has subclasses such as UITableView and UITextView.

scrollsToTop is a property of UIScrollView, which is mainly used to scroll back to the top when the control with scrollsToTop == YES is clicked on the status bar of the device.

For each default instance of UIScrollView, its scrollsToTop property defaults to YES, so to implement a UIScrollView instance to click the device status bar to return to the top, you need to close the scrollsToTop property of other UIScrollView instances to NO. It's easy to understand: if multiple scrollViews respond to the event of returning to the top, the system will not know which scrollView to return to the top, so it will not do anything. . .

Take a chestnut:

Only when a UIViewController controller has a scrollview and set this property to yes,

Other scrollview.scrollsToTop = NO will respond to this event. The principle is very simple. If there are 3 scrollviews, the system will not know which one you need to scroll to the top.

        For example, there are three UIView views in a UIViewController, namely   _pushList,   _photoList,   _starList, and each view has a UITableView, the settings are as follows:

    

        _pushList.table.scrollsToTop = YES;

        _photoList.table.scrollsToTop = NO;

        _starList.table.scrollsToTop = NO;

Understand? It should be noted that UIWebView contains subview UIWebViewScrollView, which is also a subclass of UIScrollView. I didn’t realize this at the beginning, which made it impossible to click the status bar to return to the top. Set the scrollsToTop of UIWebViewScrollView to NO, which is normal.