@State屬性值在sheet(item:)方法中呼叫時不會保留

在下面的代碼中，我有一個可選的@State變數呼叫isReseting，我true通過點擊一個按鈕來設定它。該按鈕也觸發時，它的拍了拍片，這是作業的罰款，但什么行不通的是，如果我讀的價值isResting里面的變數.sheet它輸出作為nil和我期待這是true因為它被設定為true當按鈕被點擊。

任何想法，為什么值isReseting變數變成nil里面的.sheet？

struct Item: Identifiable{
    var id = UUID()
    var name:String
    var active:Bool
}

struct ContentView: View {
    
    var items:[Item] = [Item(name: "Oranges", active: true),
                    Item(name: "Apples", active: false),
                    Item(name: "Cookies", active: false) ]
    
    @State private var selectedItem: Item?
    @State private var isReseting: Bool?
        
    var body: some View {
        List{
            ForEach(items){ item in
                HStack{
                    Text(item.name)
                    
                    Button(item.active ? "Reset": "Initiate"){
                        selectedItem = item
                        isReseting = true
                        let _ = print("Value after button tap: \(isReseting)")// output: Value after button tap: Optional(true)
                    }
                    .padding()
                    .background(item.active ? Color.blue: Color.gray)
                    .foregroundColor(.white)
                    .cornerRadius(30)
                    .frame(width: 100, height: 65)
                }
            }
        }
        .sheet(item: $selectedItem){ item in
            // I'm expecting isReseting to be true here, but it's nil
            let _ = print("Value in sheet: \(isReseting)")// outputs: Value in sheet: nil
            
            if isReseting == true {
                Text("It's reseting!!!")
            }else{
                Text("It's NOT reseting")
            }
        }
    }
}

uj5u.com熱心網友回復：

我認為您會被這樣一個事實所吸引，即sheet(item:) 僅基于item- 而不是封裝視圖的@State變數重新渲染。只要您明確isReseting通過item，它就會起作用：

struct Item: Identifiable, Equatable {
    var id = UUID()
    var name:String
    var active:Bool
}

struct ContentView: View {
    
    var items:[Item] = [Item(name: "Oranges", active: true),
                    Item(name: "Apples", active: false),
                    Item(name: "Cookies", active: false) ]
    
    struct SheetItem : Identifiable {
        var item: Item
        var isReseting: Bool
        
        var id: UUID {
            self.item.id
        }
    }
    
    @State private var selectedItem: SheetItem?
    @State private var isReseting: Bool?
        
    var body: some View {
        List{
            ForEach(items){ item in
                HStack{
                    Text(item.name)
                    
                    Button(item.active ? "Reset": "Initiate"){
                        isReseting = true
                        selectedItem = SheetItem(item: item, isReseting: isReseting ?? false)
                    }
                    .padding()
                    .background(item.active ? Color.blue: Color.gray)
                    .foregroundColor(.white)
                    .cornerRadius(30)
                    .frame(width: 100, height: 65)
                }
            }
        }
        .sheet(item: $selectedItem) { item in
            let _ = print("Value in sheet: \(item.isReseting)")
            
            if item.isReseting == true {
                Text("It's reseting!!!")
            } else {
                Text("It's NOT reseting")
            }
        }
    }
}

實作此目的的第二種方法是顯式傳遞 a Binding（即使您不需要在作業表中對其進行變異），因為它將保持與@State變數的鏈接：

struct Item: Identifiable{
    var id = UUID()
    var name:String
    var active:Bool
}

struct ContentView: View {
    
    var items:[Item] = [Item(name: "Oranges", active: true),
                    Item(name: "Apples", active: false),
                    Item(name: "Cookies", active: false) ]
    
    @State private var selectedItem: Item?
    @State private var isReseting: Bool?
        
    var body: some View {
        List{
            ForEach(items){ item in
                HStack{
                    Text(item.name)
                    
                    Button(item.active ? "Reset": "Initiate"){
                        selectedItem = item
                        isReseting = true
                        let _ = print("Value after button tap: \(isReseting)")// output: Value after button tap: Optional(true)
                    }
                    .padding()
                    .background(item.active ? Color.blue: Color.gray)
                    .foregroundColor(.white)
                    .cornerRadius(30)
                    .frame(width: 100, height: 65)
                }
            }
        }
        .sheet(item: $selectedItem){ item in
            // I'm expecting isReseting to be true here, but it's nil
            SheetView(isReseting: $isReseting)
        }
    }
}

struct SheetView : View {
    @Binding var isReseting : Bool?
    
    var body: some View {
        let _ = print("Value in sheet: \(isReseting)")// outputs: Value in sheet: nil
        
        if isReseting == true {
            Text("It's reseting!!!")
        }else{
            Text("It's NOT reseting")
        }
    }
}

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