Swift 4中touchesBegan失效：自定义UIView无法响应触摸事件

Hey there! Let’s work through why your custom SelectionView isn’t triggering those touch methods—this is a super common gotcha in UIKit, so I’ve got a few key things to check:

Common Causes & Fixes #

1. Ensure isUserInteractionEnabled is Enabled #

Even though UIView defaults this property to true, it’s easy to accidentally disable it (either in code or Interface Builder). Double-check:

• In code, add this to your SelectionView’s initializers:

  override init(frame: CGRect) {
      super.init(frame: frame)
      self.isUserInteractionEnabled = true
  }
  
  required init?(coder: NSCoder) {
      super.init(coder: coder)
      self.isUserInteractionEnabled = true
  }
  

• In Storyboard/XIB: Select your SelectionView, go to the Attributes Inspector, and make sure "User Interaction Enabled" is checked.

2. Check for Overlapping Subviews #

If there’s another view sitting on top of your SelectionView (and that top view has isUserInteractionEnabled = true), it’ll steal all the touch events. Either:

• Remove or reorder the overlapping view so it’s behind your SelectionView
• Set the overlapping view’s isUserInteractionEnabled = false if it doesn’t need to respond to touches.

3. Verify View Visibility & Alpha #

UIKit ignores touch events for views that are:

• isHidden = true
• alpha < 0.01
  Make sure your SelectionView is visible and has an alpha value of at least 0.01 (most cases you’ll want alpha = 1.0).

4. Check for Custom Hit-Test Overrides #

If your SelectionView (or any of its parent views) overrides hitTest(_:with:) or point(inside:with:), a bug in that code might be preventing touches from reaching your view. For example, if point(inside:with:) returns false when it should return true, your view won’t get the touch event. Review those methods to ensure they’re correctly implemented.

5. Validate View Frame/Position #

Sometimes your SelectionView might have a zero frame, or be positioned off-screen—so you think you’re touching it, but you’re not. Add a quick debug check in your view controller’s viewDidAppear(_:):

override func viewDidAppear(_ animated: Bool) {
    super.viewDidAppear(animated)
    print("SelectionView frame: \(selectionView.frame)")
}

You can also add a background color to SelectionView to visually confirm its position:

override init(frame: CGRect) {
    super.init(frame: frame)
    self.backgroundColor = UIColor.red.withAlphaComponent(0.5) // Visible debug color
}

Give these fixes a try—chances are one of them will get your touch events firing again!

内容的提问来源于stack exchange，提问作者Parv Bhasker