自定义继承UIScrollView的MyScrollView使用contentMode属性是否有副作用？

Hey there! Let's break down whether setting contentMode on your MyScrollView (a subclass of UIScrollView) will cause unexpected side effects.

First, let's clarify what contentMode actually does: it's a UIView property that controls how a view's own drawn content (like what you render in drawRect(_:), or the contents of its layer) scales and aligns when the view's bounds change. This is important because UIScrollView's core functionality revolves around its scrollable content (the subviews inside it, governed by contentSize, contentOffset, etc.)—and that's a separate system from the view's own layer content.

Here's how it plays out for your custom scroll view:

• If you don't do custom drawing in MyScrollView: Setting contentMode will have no meaningful side effects. By default, a UIScrollView doesn't draw any custom content (beyond its background color), so adjusting contentMode won't impact scrolling behavior, subview layout, contentSize, or any other scroll-related features. It's essentially a no-op here.

• If you do custom drawing in MyScrollView: contentMode will affect how your custom-drawn content behaves when the scroll view's bounds change (e.g., device rotation). For example, if you set .scaleAspectFit, your drawn content will scale to fit the scroll view's bounds while maintaining its aspect ratio. This is an expected behavior, not a side effect—just make sure this aligns with what you want for your custom content.

A common mistake to avoid: Don't confuse contentMode with UIScrollView-specific properties like contentInset, contentOffset, or the autoresizing rules/AutoLayout constraints of your scrollable subviews. These control the positioning and scrolling of the content inside the scroll view, and contentMode has zero impact on them.

Bottom Line #

As long as you understand that contentMode only affects the scroll view's own drawn content (not its scrollable subviews), you won't run into unexpected issues. If your MyScrollView doesn't do custom drawing, you can set contentMode freely without worrying about breaking scrolling functionality. If it does include custom drawing, just use contentMode to control that content's behavior intentionally.

内容的提问来源于stack exchange，提问作者tucan9389