如何在 SwiftUI 中更新单个子视图？

Question

我正在尝试在子视图和父视图之间建立 SwiftUI 连接。通过点击任何子视图，我只想重绘被点击的视图，而不是整个父视图。

下面的当前实现不允许您在单击视图时重绘视图，因为它具有派生值。

我通过将 BindableObject 协议添加到 CustomColor 尝试了不同的方案，但没有成功。

class CustomColor: Identifiable {

    let id = UUID()
    var color: Color

    init(color: Color) {
        self.color = color
    }

    func change(to color: Color) {
        self.color = color
    }

}

class ColorStore: BindableObject {

    var colors: [CustomColor] = [] {
        didSet {
            didChange.send(self)
        }
    }

    var didChange = PassthroughSubject<ColorStore, Never>()

    init() {
        self.colors = Array.init(repeating: CustomColor(color: .red), count: 10)
    }

}


struct ContentView: View {

    @EnvironmentObject var colorStore: ColorStore

    var body: some View {
        NavigationView {
            List {
                ForEach(colorStore.colors) { color in
                    ColorShape(color: color)
                }
            }.navigationBarTitle(Text("Colors"))
        }
    }

}

struct ColorShape: View {

    var color: CustomColor

    var body: some View {
        Button(action:
            { self.color.change(to: .blue) }
            , label: {
            ShapeView(shape: Circle(), style: color.color)
        })
    }

}

Answer 1

目前无法更新特定的子视图，我认为也不能期望。正如在 Data flow Through Swift UI 会话中所说，一旦您更改了 @State 属性或 Bindable 对象 - 所有更改都会向下流过视图层次结构，SwiftUI 框架正在比较所有视图并仅再次呈现已更改的内容。

Answer 2

我想我找到了解决办法。第一个问题是我通过重复相同的元素而不是添加独立的元素来初始化颜色数组。

更重要的是 CustomColor 本身应该具有 BindableObject 一致性，而不是模型（我们不更改颜色数组，我们更改每种颜色）。最后，我们不需要将对象包装在 ForEach 元素中（这样我们就失去了可重用性），而是将它们放在 List 元素中。

使用此实现，只会重绘已更改的视图，而不是整个集合。

代码如下：

class CustomColor: BindableObject, Identifiable {

    var didChange = PassthroughSubject<CustomColor, Never>()

    let id = UUID()
    var color: Color {
        didSet {
            self.didChange.send(self)
        }
    }

    init(color: Color) {
        self.color = color
    }

    func change(toColor color: Color) {
        self.color = color
    }

}

class ColorStore {

    var colors: [CustomColor] = []

    init() {
        (0...10).forEach { _ in colors.append(CustomColor(color: .red)) }
    }

}


struct ContentView: View {

    let colorStore: ColorStore

    var body: some View {
        NavigationView {
            List(colorStore.colors) { color in
                ColorShape(color: color)
            }.navigationBarTitle(Text("Colors"))
        }
    }

}

struct ColorShape: View {

    @ObjectBinding var color: CustomColor

    var body: some View {
        Button(action: { self.color.change(toColor: .blue) }, label: {
            ShapeView(shape: Circle(), style: color.color)
        })
    }

}

Answer 3

我可以提供三个有细微差别的版本。所有这些都切换单个按钮并保持整个模型 - ColorStore var 同步。允许添加和删除颜色数组中的元素。还要注意，我们可以不用 Identifiable 数组元素的一致性来列出它们。

版本1.最接近问题：所有型号都是classes.

class CustomColor: ObservableObject, Identifiable {

    var didChange = PassthroughSubject<CustomColor, Never>()

    let id = UUID()
    var color: Color {
        didSet {
            objectWillChange.send()
        }
    }

    init(color: Color) {
        self.color = color
    }

    func change(to color: Color) {
        self.color = color
    }

}

class ColorStore: ObservableObject {

    var didChange = PassthroughSubject<ColorStore, Never>()

    var colors: [CustomColor] = [] {
        didSet {
            objectWillChange.send()
        }
    }

    init() {
        (0...10).forEach { _ in colors.append(CustomColor(color: .red)) }
    }

}


struct ContentView: View {

    @ObservedObject var colorStore: ColorStore = ColorStore()

    var body: some View {
        NavigationView {
            List(colorStore.colors) { c in
                    ColorShape(color: c)
            }
// will work without `Identifiable`
//            List(colorStore.colors.indices, id: \.self) { c in
//                    ColorShape(color: self.colorStore.colors[c])
//            }
            .navigationBarTitle(Text("Colors"))
            .navigationBarItems(leading:
                Button(action: { self.colorStore.colors.append(CustomColor(color: .green)) }) {
                    Text("Add")
                }, trailing:
                Button(action: {
                    self.colorStore.colors.removeLast()
                    print(self.colorStore.colors)
                }, label: { Text("Remove") }))
        }
    }

}

struct ColorShape: View {

    @ObservedObject var color: CustomColor

    var body: some View {
        Button(action:
            { self.color.change(to: .blue)
                print(self.color)
        }
            , label: {
                Circle().fill(color.color)
        })
    }

}

版本 2。CustomColor 被重写为结构。

// No need for manual `ObservableObject, Identifiable` conformance
struct CustomColor /*: Identifiable */ {

    // let id = UUID()
    var color: Color

    init(color: Color) {
        self.color = color
    }

    mutating func change(to color: Color) {
        self.color = color
    }

}

class ColorStore: ObservableObject {

    var didChange = PassthroughSubject<ColorStore, Never>()
    // If `CustomColor` is a `struct` i.e. value type, we can populate array with independent values, not with the same reference by using `repeating:` init.
    var colors: [CustomColor] = Array(repeating: CustomColor(color: .red), count: 10) {
        didSet {
            objectWillChange.send()
        }
    }

    /* init() {
        (0...10).forEach { _ in colors.append(CustomColor(color: .red)) }
    } */

}


struct ContentView: View {

    @ObservedObject var colorStore: ColorStore = ColorStore()

    var body: some View {
        NavigationView {
            List {
                // Strange, bu if we omit ForEach, we will get an error on element removal from array.
                ForEach(colorStore.colors.indices, id: \.self)
                { c in
                    ColorShape(color: self.$colorStore.colors[c])
                }

            }
            .navigationBarTitle(Text("Colors"))
            .navigationBarItems(leading:
                Button(action: { self.colorStore.colors.append(CustomColor(color: .green)) }) {
                    Text("Add")
                }, trailing:
                Button(action: {
                    self.colorStore.colors.removeLast()
                    print(self.colorStore.colors)
                }, label: { Text("Remove") }))
        }
    }

}

struct ColorShape: View {

    @Binding var color: CustomColor

    var body: some View {
        Button(action:
            { self.color.change(to: .blue)
                print(self.color)
        }
            , label: {
                Circle().fill(color.color)
        })
    }

}

版本 3。主模型 ColorStore 及其子类型 CustomColor 被重写为结构。无需手动符合ObservableObject.

struct CustomColor /* : Identifiable */ {

    // let id = UUID()
    var color: Color

    init(color: Color) {
        self.color = color
    }

    mutating func change(to color: Color) {
        self.color = color
    }

}

struct ColorStore {
    // If `CustomColor` is a `struct` i.e. value type, we can populate array with independent values, not with the same reference by using `repeating:` init.
    var colors: [CustomColor] = Array(repeating: CustomColor(color: .red), count: 10)

}


struct ContentView: View {

    @State var colorStore: ColorStore = ColorStore()

    var body: some View {
        NavigationView {
            List{
                ForEach(colorStore.colors.indices, id: \.self) { i in
                    return ColorShape(color: self.$colorStore.colors[i])
                }
            }
            .navigationBarTitle(Text("Colors"))
            .navigationBarItems(leading:
                Button(action: { self.colorStore.colors.append(CustomColor(color: .green)) }) {
                    Text("Add")
            }, trailing:
                // Removing causes index out of bound error (bug?)
                Button(action: {
                    self.colorStore.colors.removeLast()
                    print(self.colorStore.colors)}) {
                    Text("Remove") })
        }
    }
}

struct ColorShape: View {

    @Binding var color: CustomColor

    var body: some View {
        Button(action: {
            self.color.change(to: .blue)
            print(self.color)
        }) {
            Circle().fill(color.color)
        }
    }
}

如何在 SwiftUI 中更新单个子视图？

How to update a single child view in SwiftUI?

swiftui