如何为多个类Swift进行扩展

Question

I have an extension:

extension UILabel {
    func animateHidden(flag: Bool) {
        self.hidden = flag
    }
}

I need to make the same one for UIImageView but I don't want to copy that whole code. Is it possible to make an extension for multiple classes?

Thanks.

Answer 1

You could make a protocol and extend it.

Something like:

protocol Animations {
    func animateHidden(flag: Bool)
}

extension Animations {
    func animateHidden(flag: Bool) {
        // some code
    }
}

extension UILabel: Animations {}

extension UIImageView: Animations {}

Your method will be available for the extended classes:

let l = UILabel()
l.animateHidden(false)

let i = UIImageView()
i.animateHidden(false)

In a comment, you've asked: "in this case how to call self for UILabel and UIImageView in animateHidden function?". You do that by constraining the extension.

Example with a where clause:

extension Animations where Self: UIView {
    func animateHidden(flag: Bool) {
        self.hidden = flag
    }
}

Thanks to @Knight0fDragon for his excellent comment about the where clause.

Answer 2

Best Method to Extend UILabel & UIImageView Together

Swift 4.1 / Xcode 9.4

A much better way to do this in your case would be to just extend UIView . This works because both UILabel and UIImageView both inherit from UIView .

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Extension

extension UIView {
    func animateHidden(flag: Bool) {
        self.hidden = flag
    }
}

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Usage of animateHidden(flag: Bool) Extension

Declaration of label and imageView :

label = UILabel()
imageView = UIImageView()

Actual usage of extension

label.animateHidden(flag: true)
imageView.animateHidden(flag: false)

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Bonus - Other Classes that many UI Components Conform to

If you would like to have your extension be able to conform with many different types of UI components, there are 4 types that a very large amount of UI components conform to:

1. CVarArg
2. Equatable
3. Hashable
4. NSCoding

Some of the many UI components include:

• UILabel: CVarArg , Equatable , Hashable , NSCoding

• UITextField: CVarArg , Equatable , Hashable , NSCoding

• UITableViewCell: CVarArg , Equatable , Hashable , NSCoding

• UITextView: CVarArg , Equatable , Hashable , NSCoding

• UITableView: CVarArg , Equatable , Hashable , NSCoding

• UIImage: CVarArg , Equatable , Hashable , NSCoding

• UIPickerView: CVarArg , Equatable , Hashable , NSCoding

• UIView: CVarArg , Equatable , Hashable , NSCoding

• UIImageView: CVarArg , Equatable , Hashable , NSCoding

• UINavigationBar: CVarArg , Equatable , Hashable , NSCoding

• UIButton: CVarArg , Equatable , Hashable , NSCoding

• UIBarButtonItem: CVarArg , Equatable , Hashable , NSCoding

• UIStackView: CVarArg , Equatable , Hashable , NSCoding

• UIToolbar: CVarArg , Equatable , Hashable , NSCoding

• UITabBar: CVarArg , Equatable , Hashable , NSCoding

• UITabBarItem: CVarArg , Equatable , Hashable , NSCoding

• UIScrollView: CVarArg , Equatable , Hashable , NSCoding

• UISplitViewController: CVarArg , Equatable , Hashable , NSCoding

• UIViewController: CVarArg , Equatable , Hashable , NSCoding

• UIScreen: CVarArg

• UISwitch: CVarArg , Equatable , Hashable , NSCoding

• UISlider: CVarArg , Equatable , Hashable , NSCoding

• UIAlertAction: CVarArg

• UIAlertController: CVarArg , Equatable , Hashable , NSCoding

• UIImageAsset: CVarArg , Equatable , Hashable , NSCoding

• UIDatePicker: CVarArg , Equatable , Hashable , NSCoding

• UINib: CVarArg

• UIResponder: CVarArg

• UIWindow: CVarArg , Equatable , Hashable , NSCoding

• UIRegion: CVarArg , Equatable , Hashable , NSCoding

• UIControl: CVarArg , Equatable , Hashable , NSCoding

• UIBezierPath: CVarArg , Equatable , Hashable , NSCoding

• UIVisualEffect: CVarArg , Equatable , Hashable , NSCoding

• UISearchBar: CVarArg , Equatable , Hashable , NSCoding

• UIMenuItem: CVarArg

• UIMenuController: CVarArg

• UIStoryboard: CVarArg

• And many more...

This means that by extending either CVarArg , Equatable , Hashable , or NSCoding , you can extend most (if every not every) UI component.

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Well anyways, I hope this all helps you resolve your issue and if you have absolutely any questions, suggestions, etc., feel free to ask!

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