Question 250535 in IOS Swift Question posted in
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Ios swift – Injecting SwiftUI ViewModifiers giving error: Type 'any ViewModifier' cannot conform to 'ViewModifier'

I would like to inject my ViewModifier from a ViewModel which depends on user configuration.

Below code is a View which has a ViewModel. ViewModel can be created with ViewConfiguration and user should be able to either use a default style or custom style based on preferences.

When I try to do this it gives me error on View which says

Type ‘any ViewModifier’ cannot conform to ‘ViewModifier’


struct FeatureUnavailableView: View {
    
    var viewModel = ViewModel(config: ViewConfiguration(titleStyle: DefaultTitleModifier()))
    
    var body: some View {
        Text("Hello World")
            .modifier(viewModel.config.titleStyle)
    }
}

class ViewModel {
    
    let config: ViewConfiguration
    
    init(config: ViewConfiguration) {
        self.config = config
    }
}

struct ViewConfiguration {
    
    var titleStyle: any ViewModifier
}

public struct DefaultTitleModifier: ViewModifier {
    
    public func body(content: Content) -> some View {
        content
            .lineLimit(1)
            .foregroundColor(.red)
            .bold()
    }
}
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2

Answers


  1. 0

    Rather than using any ViewModifier you need to use generics to set the type as a concrete ViewModifier type when the ViewConfiguration struct and ViewModel class are initialised.

    struct ViewConfiguration<T: ViewModifier> {
    
    var titleStyle: T
}

class ViewModel<T: ViewModifier> {
    
    let config: ViewConfiguration<T>
    
    init(config: ViewConfiguration<T>) {
        self.config = config
    }
}
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  2. 0

    Views don’t belong in Models, but you can use Models to make a View dynamic.

    Instead of expecting any ViewModifier you can expect ViewModiferModel.

    struct ViewConfiguration {
    
    var titleStyle: ViewModifierModel
    
}

    Then store and transmit any values with that model.

    struct ViewModifierModel: Equatable {
    var color: UIColor
    var isBold: Bool
    var lineLimit: Int
    
    static let `default` = ViewModifierModel(color: .red, isBold: true, lineLimit: 1)
    static let two = ViewModifierModel(color: .orange, isBold: false, lineLimit: 2)
}

    The modifier itself would switch from hardcoded values to the values in the model.

    public struct DefaultTitleModifier: ViewModifier {
    let model: ViewModifierModel
    public func body(content: Content) -> some View {
        content
            .lineLimit(model.lineLimit)
            .foregroundColor(Color(model.color))
            .bold(model.isBold)
    }
}
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