SwiftUI add subview dynamically but the animation doesn't work

问题

I would like to create a view in SwiftUI that add a subview dynamically and with animation.

struct ContentView : View {
    @State private var isButtonVisible = false

    var body: some View {
        VStack {
            Toggle(isOn: $isButtonVisible.animation()) {
                Text("add view button")
            }

           if isButtonVisible {
                 AnyView(DetailView())
                      .transition(.move(edge: .trailing))
                      .animation(Animation.linear(duration: 2))
             }else{
                    AnyView(Text("test"))
            }
        }
    }
}

The above code works fine with the animation . however when i move the view selection part into a function, the animation is not working anymore (since i want to add different views dynamically, therefore, I put the logic in a function.)


struct ContentView : View {
    @State private var isButtonVisible = false
    var body: some View {
        VStack {
            Toggle(isOn: $isButtonVisible.animation()) {
                Text("add view button")
            }

            subView().transition(.move(edge: .trailing))
                     .animation(Animation.linear(duration: 2))   
    }

     func subView() -> some View {
         if isButtonVisible {
             return AnyView(DetailView())
         }else{
            return AnyView(Text("test"))
        }
    }
}

it looks totally the same to me, however, i don't understand why they have different result. Could somebody explain me why? and any better solutions? thanks alot!

回答1:

Here's your code, modified so that it works:

struct ContentView : View {
    @State private var isButtonVisible = false

    var body: some View {
        VStack {
            Toggle(isOn: $isButtonVisible.animation()) {
                Text("add view button")
            }

            subView()
                .transition(.move(edge: .trailing))
                .animation(Animation.linear(duration: 2))
        }
    }

    func subView() -> some View {
        Group {
            if isButtonVisible {
                DetailView()
            } else {
                Text("test")
            }
        }
    }
}

Note two things:

Your two examples above are different, which is why you get different results. The first applies a transition and animation to a DetailView, then type-erases it with AnyView. The second type-erases a DetailView with AnyView, then applies a transition and animation.
Rather that using AnyView and type-erasure, I prefer to encapsulate the conditional logic inside of a Group view. Then the type you return is Group, which will animate properly.
If you wanted different animations on the two possibilities for your subview, you can now apply them directly to DetailView() or Text("test").

Update

The Group method will only work with if, elseif, and else statements. If you want to use a switch, you will have to wrap each branch in AnyView(). However, this breaks transitions/animations. Using switch and setting custom animations is currently not possible.

来源：https://stackoverflow.com/questions/58160011/swiftui-add-subview-dynamically-but-the-animation-doesnt-work

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ios

swift

iphone

swiftui

swift5