SwiftUI - 在视图模型数组中更新模型的刷新视图答案

【问题标题】：SwiftUI - Refresh view on model updated in view model arraySwiftUI - 在视图模型数组中更新模型的刷新视图
【发布时间】：2021-06-01 21:02:54
【问题描述】：

要问的问题很简单，但我可能忘记了代码中的某些内容。
让我们用一张图片更好地解释一下：

在选择/取消选择项目时，我基本上需要更新“COUNT”和“PRICE”。

我有这样的代码结构：

型号：

class ServiceSelectorModel: Identifiable, ObservableObject {
    var id = UUID()

    var serviceName: String
    var price: Double
    
    init(serviceName: String, price: Double) {
        self.serviceName = serviceName
        self.price = price
    }

    @Published var selected: Bool = false
}

视图模型：

class ServiceSelectorViewModel: ObservableObject {
    @Published var services = [ServiceSelectorModel]()

    init() {
        self.services = [
            ServiceSelectorModel(serviceName: "SERVICE 1", price: 1.80),
            ServiceSelectorModel(serviceName: "SERVICE 2", price: 10.22),
            ServiceSelectorModel(serviceName: "SERVICE 3", price: 2.55)
        ]
    }
}

切换视图

struct ServiceToggleView: View {
    @ObservedObject var model: ServiceSelectorModel
    
    var body: some View {
        VStack(alignment: .center) {
            HStack {
                Text(model.serviceName)
                
                Toggle(isOn: $model.selected) {
                    Text(String(format: "€ +%.2f", model.price))
                        .frame(maxWidth: .infinity, alignment: .trailing)
                }
            }
            .background(model.selected ? Color.yellow : Color.clear)
        }
    }
}

ServiceSelectorView

struct ServiceSelectorView: View {

    @ObservedObject var serviceSelectorVM = ServiceSelectorViewModel()

    var body: some View {
        VStack {
            VStack(alignment: .leading) {
                ForEach (serviceSelectorVM.services, id: \.id) { service in
                    ServiceToggleView(model: service)
                }
            }

            let price = serviceSelectorVM.services.filter{ $0.selected }.map{ $0.price }.reduce(0, +)

            Text("SELECTED: \(serviceSelectorVM.services.filter{ $0.selected }.count)")
            Text(String(format: "TOTAL PRICE: €%.2f", price))    
        }
    }
}

在这段代码中，我可以更新模型的selected 状态，但包含所有模型的视图模型应该刷新PRICE 不更新。
好像数组中的模型没有变化。

我忘记了什么？

【问题讨论】：

标签： ios swift mvvm swiftui observable

【解决方案1】：

可能最简单的方法是将模型设为值类型，然后更改其属性，持有它的视图模型将被更新。并更新视图以使用绑定到这些值

struct ServiceSelectorModel: Identifiable {
    var id = UUID()

    var serviceName: String
    var price: Double
    
    init(serviceName: String, price: Double) {
        self.serviceName = serviceName
        self.price = price
    }

    var selected: Bool = false
}

struct ServiceToggleView: View {
    @Binding var model: ServiceSelectorModel
...
}

...

ForEach (serviceSelectorVM.services.indices, id: \.self) { i in
    ServiceToggleView(model: $serviceSelectorVM.services[i])
}

注意：内联编写，未经测试，可能需要修复一些错字

【讨论】：

别担心错字，我只需要关于如何修复的建议，而不是复制/粘贴:)

【解决方案2】：

如果您仔细观察，您已经创建了两个不同的单一事实来源。这就是父母没有更新的原因，因为它没有链接到孩子。

一种方法是将ServiceSelectorModel 创建为结构，并在子视图中将services 数组作为@Binding 传递。下面是工作示例。

ViewModel-:

struct ServiceSelectorModel {
    
    var id = UUID().uuidString
    var serviceName: String
    var price: Double
    var isSelected:Bool = false
    
    init(serviceName: String, price: Double) {
        self.serviceName = serviceName
        self.price = price
    }
    
}

class ServiceSelectorViewModel: ObservableObject,Identifiable {
    
    @Published var services = [ServiceSelectorModel]()
    
    var id = UUID().uuidString
    init() {
        self.services = [
            ServiceSelectorModel(serviceName: "SERVICE 1", price: 1.80),
            ServiceSelectorModel(serviceName: "SERVICE 2", price: 10.22),
            ServiceSelectorModel(serviceName: "SERVICE 3", price: 2.55)
        ]
    }
}

观看次数-：

struct ServiceToggleView: View {
    @Binding var model: [ServiceSelectorModel]
    
    var body: some View {
        VStack(alignment: .center) {
            ForEach(0..<model.count) { index in
                HStack{
                    Text(model[index].serviceName)
                    Toggle(isOn: $model[index].isSelected) {
                        Text(String(format: "€ +%.2f", model[index].price))
                            .frame(maxWidth: .infinity, alignment: .trailing)
                    }
                }.background(model[index].isSelected ? Color.yellow : Color.clear)
            }
            
        }
    }
}

struct ServiceSelectorView: View {
    
    @ObservedObject var serviceSelectorVM = ServiceSelectorViewModel()
    
    var body: some View {
        VStack {
            VStack(alignment: .leading) {
                ServiceToggleView(model: $serviceSelectorVM.services)
            }
            
            let price = serviceSelectorVM.services.filter{ $0.isSelected }.map{ $0.price }.reduce(0, +)
            
            Text("SELECTED: \(serviceSelectorVM.services.filter{ $0.isSelected }.count)")
            Text(String(format: "TOTAL PRICE: €%.2f", price))
        }
    }
}

【讨论】：