How to make extension for multiple classes Swift

问题

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.

回答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.

回答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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来源：https://stackoverflow.com/questions/38464134/how-to-make-extension-for-multiple-classes-swift