How to put a function that returns void in SwiftUI Preview's parameters

user_12039062 0
Viewed 1293

I'm trying to use this function:

var handler: (String, (Bool) -> Void) -> Void

And the error displayed in the preview provider is that there's a missing argument for the parameter in call, but I don't know how to do that properly.

Insert ', handler: <#(String, (Bool) -> Void) -> Void#>'

If you have some documentation or explanation about handling these types of data in the preview provider I'd be really grateful.

swiftui
3 Answers

This is a little tricky because of the closure-within-a-closure. Xcode doesn't seem to want to inline the second closure, but assuming it's defined outside of it, it seems to work fine:

struct MyView : View {
    var handler: (String, (Bool) -> Void) -> Void
    
    var body: some View {
        Text("Hello, world")
    }
}

struct TestView_Preview : PreviewProvider {
    static var boolHander : (Bool) -> Void = { _ in }
    
    static var previews: some View {
        MyView(handler:{ myString, boolHander in })
    }
}

I'm making some assumptions here, since you didn't actually include any code showing where/how it was defined, but hopefully this gets you moving in the right direction.

user_5609420

It seems that the problem was that there was no initial value for "handler", which is taken somehow as a Binding, so the preview provider and the parent view asked for the value.

Putting = { _ , _ in } as the initial value for "handler" solved the problem.

user_120390620 
struct MyView: View {
    var handler: () -> ()

    var body: some View {
    Text("Hello, world")
   }
}

struct MyView_Preview: PreviewProvider {    
  static var previews: some View {
     MyView(handler: {})
   }
}

and this for two closures: 

struct MyView: View {
var handler: (() -> ()) -> ()

var body: some View {
    Text("Hello, World!")
 }
}

struct MyView_Previews: PreviewProvider {
static var previews: some View {
    MyView(handler: { _ in } )
  }
}
user_178252200
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