问题

我有一个简单的按钮，在模拟器上按预期工作，形状会随点击而变;

```swift
结构体 ButtonTest: View {
    @State var isLiked = true
    var body: some View {

        VStack {
            LikeButtonSimple( action: toggleLiked, isLiked: $isLiked)
        }
    }
    func toggleLiked() {
    
        isLiked.toggle()
        print("Liked Button: \(isLiked)")
    }
}

结构体 LikeButtonSimple: View {
    
    let dimen = 50.0
    let dimenHalf = CGFloat(28)
    
    var action: () -> Void?
    
    @Binding var isLiked : Bool

    var body: some View {
        ZStack {
            Circle()
                .frame(width: dimen, height: dimen)
                .foregroundColor(.white )
                .shadow(color: .black, radius: 2, y: 2)
            Button( action: {
               action()
            }
            ) {
                Image(systemName: isLiked ? "heart.fill" : "heart")
                    .resizable()
                    .foregroundColor(isLiked ? .red : .gray)
                    .frame(width: dimenHalf, height: dimenHalf)
            }
        }
    }
}

我想在 Preview 上看到相同的行为，为此编写了以下内容;

结构体 LikeButtonSimple_Previews: PreviewProvider {

    @State static var isLiked = true

    static func toggleLiked() {

        isLiked.toggle()
    }

    static var previews: some View {
        LikeButtonSimple( action: toggleLiked, isLiked: $isLiked)

    }
}

按钮不再切换。我们能在 Preview 中使用这个 PreviewProvider 来解决吗？

<details>
<summary>英文:</summary>

I&#39;ve a simple button that work on simulator as expected, the shape changes with click;

```swift
struct ButtonTest: View {
    @State var isLiked = true
    var body: some View {

        VStack {
            LikeButtonSimple( action: toggleLiked, isLiked: $isLiked)
        }
    }
    func toggleLiked() {
    
        isLiked.toggle()
        print(&quot;Liked Button: \(isLiked)&quot;)
    }
}

struct LikeButtonSimple: View {
    
    let dimen = 50.0
    let dimenHalf = CGFloat(28)
    
    var action: () -&gt; Void?
    
    @Binding var isLiked : Bool

    var body: some View {
        ZStack {
            Circle()
                .frame(width: dimen, height: dimen)
                .foregroundColor(.white )
                .shadow(color: .black, radius: 2, y: 2)
            Button( action: {
               action()
            }
            ) {
                Image(systemName: isLiked ? &quot;heart.fill&quot; : &quot;heart&quot;)
                    .resizable()
                    .foregroundColor(isLiked ? .red : .gray)
                    .frame(width: dimenHalf, height: dimenHalf)
            }
        }
    }
}

I want to see the same behavior on the Preview as well and wrote the below for it;

struct LikeButtonSimple_Previews: PreviewProvider {

    @State static var isLiked = true

    static func toggleLiked() {

        isLiked.toggle()
    }

    static var previews: some View {
        LikeButtonSimple( action: toggleLiked, isLiked: $isLiked)

    }
}

The button doesn't toggle anymore. Can we work this on Preview with this PreviewProvider?

答案1

得分: 2

由于Xcode的“预览”是静态的，无法保存变量的更改值。

要在“预览”中更改值，您将需要使用其中包含状态值的容器视图。

struct LikeButtonSimple_Previews: PreviewProvider {
    
    //包装实际视图并保存状态变量的视图。
    struct ContainerView: View {
        @State private var isLiked = true
        
        var body: some View {
            LikeButtonSimple(action: toggleLiked, isLiked: $isLiked)
        }
        
        func toggleLiked() {
            isLiked.toggle()
        }
    }

    static var previews: some View {
        ContainerView()
    }
}

struct LikeButtonSimple_Previews: PreviewProvider {
    
    //A view which will wraps the actual view and holds state variable. 
    struct ContainerView: View {
        @State private var isLiked = true
        
        var body: some View {
            LikeButtonSimple(action: toggleLiked, isLiked: $isLiked)
        }
        
        func toggleLiked() {
            isLiked.toggle()
        }
    }

    static var previews: some View {
        ContainerView()
    }
} 

答案2

得分: 1

我认为在这里根本不需要操作。

绑定是与某些数据的双向连接。

通过使用绑定，您传递给它的视图可以对其进行更新。

因此，您不需要绑定和操作。按钮操作应该只是…

isLiked.toggle()

这就足以更新视图并在“父”视图中更新该值。

isLiked.toggle()