visandres's questions

我正在尝试使用 SwiftUI 来更好地理解它，但我无法理解这种行为上的差异。在此示例代码中，为什么结构视图能够旋转而 @ViewBuilder 函数却不能旋转？

struct ContentView: View {
    @State var isSpinning = false
    
    var body: some View {
        StructView()
        funcView()
    }
    
    @ViewBuilder
    func funcView() -> some View {
        @State var isSpinning = false
        VStack {
            Button {
                isSpinning.toggle()
            }label: {
                Text("Spin me")
            }
            Image(systemName: "arrow.clockwise")
                .font(.system(size: 80))
                .foregroundColor(.blue)
                .rotationEffect(.degrees(isSpinning ? 360 : 0))
                .animation(.easeInOut(duration: 1), value: isSpinning)
        }
        .padding()
    }
    
    struct StructView: View {
        @State var isSpinning = false
        
        var body: some View {
            VStack {
                Button {
                    isSpinning.toggle()
                }label: {
                    Text("Spin me")
                }
                Image(systemName: "arrow.clockwise")
                    .font(.system(size: 80))
                    .foregroundColor(.blue)
                    .rotationEffect(.degrees(isSpinning ? 360 : 0))
                    .animation(.easeInOut(duration: 1), value: isSpinning)
            }
            .padding()
        }
    }

}

为什么字典类型不能[String: Encodable]()转换为 Encodable？

let dictionary = [String: Encodable]()
let test = dictionary is Encodable //Returns false

但是字典[String: String]()确实有效

let dictionaryTwo = [String: String]()
let test = dictionaryTwo is Encodable //Returns true