How to create custom Modifier to manipulate custom View in SwiftUI?

Question

Context

Hi, I am currently working a lot with SwiftUI and encountered a problem while working with Modifiers. I have this basic setup:

Code

// This TitleView Protocol should be adapted by all SwiftUI Views containing a Title.
protocol TitleView: View {
    var title: String { get set }
}

// This is one of many Views containing a Title, therefore it conforms to the TitleView Protocol.
struct SomeTitleView: TitleView {
    var title: String = "Hello World";

    var body: some View {
        Text(title)
    }
}

// This Extension adds the setTitle Modifier to all Views conforming to TitleView.
extension View where View: TitleView {
    func setTitle(_ title: String) -> some View {
        self.modifier(CRStyleModifier(title: title))
    }
}

// This ViewModifier is supposed to manipulate the Title Property inside Views conforming to TitleView. 
// However, I am not sure how to accomplish it.
struct TextModifier: ViewModifier {
    let title: String
    
    @ViewBuilder func body<Content: TitleView>(content: Content) -> some View {
        content 
        // How can I update the Title Property of the Content?
        // Once I make the body Method generic, I get this error message -> Type 'CRStyleModifier' does not conform to protocol 'ViewModifier'
    }
}

Question

How can I achieve my goal of having a custom Modifier that can modify not just basic things like foregroundColor and font but also more specific ones like title on all Views conforming to a specific protocol? Thanks a lot for your help!

Why do you need a ViewModifier for that? Why don't you just do the view modification inside your setTitle extension on TitleView? — David Pasztor
– David Pasztor, Commented Mar 18, 2022 at 9:44
@DávidPásztor That is also an idea. However, how would you accomplish it there? — christophriepe
– christophriepe, Commented Mar 18, 2022 at 9:54

Asperi · Accepted Answer · 2022-03-18 09:53:48Z

5

A custom modifier is possible but is not needed in this case as would introduced unneeded complexity, instead your extension can look like

extension View where Self: TitleView {
    func setTitle(_ title: String) -> some View {
        var newView = self
        newView.title = title
        return newView
    }
}

Tested with Xcode 13.3

answered Mar 18, 2022 at 9:53

Asperi

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3 Comments

christophriepe Over a year ago

Is it also possible to add a default implementation of the title property to all Views conforming to TitleView?

Asperi Over a year ago

Yes, as for any protocol extension TitleView { var title: String get { "" } set { } } }

domi852 Over a year ago

It is better to return TitleView instead of some View because this would allow for more functions like this, e.g. func setSubtitle(_ sub: String)->Title View etc.

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