UILabel扩展，用户定义的运行时属性

Question

I would like to know more details how to implement text styles to UILabel. I want to type String in IBInspectable field in Storyboard, get this value and look for this it in style file (switch case).

I've tried to do this this way:

1. Set "User defined runtime attributes".

   Key Path as style,

   Type as

   String,

   value as "hello"

   I' ve read that I should declare also this property in UILabel class so:

     extension UILabel{ var style: String? { get(){ return self.style // it always fails } set(newValue){ objc_setAssociatedObject(self, "styleNew", newValue, objc_AssociationPolicy.OBJC_ASSOCIATION_RETAIN) //instead of self.style = newValue } } 

   }

I'm calling it in viewDidAppear method as an Outlet property:

 `print("Style", self.infoLabel.valueForKey("styleNew"))`

and also

 `print("Style", self.infoLabel.styleNew)`

When I try to get value it fails. I'm getting "bad_exc_access" error, I've tried to repair it but I don't understand this behavior and on apple.developer is nothing clear. I found only tutorials, issues with cornerRadius, borderColor and staff like that. I've tried to replace return return self.styleNew with objc_getAssociatedObject(self, "styleNew") , but it doesn't help too.

Answer 1

This is a computed property and you cannot return itself in the getter.

If you are trying to style the label by setting the style string, I suggest you keep a registry of styles and when the style attribute gets set, just apply the style to the UILabel. I tried to implement something similar with success so you can take a look here .