Xcode9.2中，IB设置命名颜色后无法通过代码修改UIView背景颜色？

Yep, you’re far from the only developer who’s run into this frustrating quirk in Xcode 9.2! Let’s break down what’s happening and how to fix it.

What’s Going On? #

When you set a view’s background color to a named color from the asset catalog via Interface Builder, Xcode 9.2 has a known timing issue: the system re-applies the IB-set color after viewDidLoad runs. That means your line of code:

view.backgroundColor = .red // 无效，IB中设置的资源颜色仍保留

gets overwritten by the named color from your asset catalog later in the view controller lifecycle (usually in viewWillLayoutSubviews or similar).

Is this normal behavior? Short answer: No, this is a bug specific to Xcode 9.x. Later versions of Xcode (10 and above) fixed this lifecycle timing mismatch, so the issue doesn’t occur there.

Fixes to Try #

Here are a few reliable workarounds:

• Move your code to a later lifecycle method: Place the background color assignment in viewWillAppear(_:) or viewDidLayoutSubviews. Just note that viewDidLayoutSubviews can be called multiple times (e.g., when the view resizes), so you might want to add a check to avoid redundant changes:

  override func viewDidLayoutSubviews() {
      super.viewDidLayoutSubviews()
      if view.backgroundColor != .red {
          view.backgroundColor = .red
      }
  }
  

• Reset the color first in viewDidLoad: Explicitly set the background color to nil before assigning your desired color. This breaks the IB color’s persistence:

  override func viewDidLoad() {
      super.viewDidLoad()
      view.backgroundColor = nil
      view.backgroundColor = .red
  }
  

• Upgrade Xcode: If possible, moving to Xcode 10 or newer eliminates the issue entirely, as Apple fixed this timing bug in those releases.

内容的提问来源于stack exchange，提问作者Joris Weimar