问编译器无法在合理的时间内在SwiftUI中对此表达式进行类型检查
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Stack Overflow用户

提问于 2019-10-17 13:42:57

回答 1查看 1.4K关注 0票数 3

我正在尝试用SwiftUI构建一个我认为很简单的表单，但在从主体返回的视图(在本例中是Form，但我也尝试过VStack)上收到错误消息“the compiler is unable to type check this expression；try up up the expression to distinct sub sections”。如果我开始删除一些子视图，它似乎解决了，即使我的视图都没有直接返回10个子视图，我认为这是单个视图的限制(除了在ForEach中返回的视图)。

import SwiftUI

struct CreateDispatchView: View {
    @State private var customerId: Int = 0
    @State private var name: String = ""
    @State private var phone: String = ""
    @State private var description: String = ""
    @State private var priorityId: Int = 0
    @State private var callTypeId: Int = 0
    @State private var bay: String = ""
    @State private var poTicket: String = ""
    @State private var outOfChemicals: Bool = false
    @State private var isReturnCall: Bool = false

    var body: some View {
        Form { // <-- Error is shown here
            Section {
                Picker("Customer", selection: $customerId) {
                    ForEach(0 ..< 10) {
                        Text("Customer \($0)")
                    }
                }
                TextField("Name", text: $name)
                TextField("Phone", text: $phone)
                TextField("Description", text: $description)
                TextField("Bay", text: $bay)
                TextField("PO ticket", text: $poTicket)
            }

            Section {

                Picker("Priority", selection: $priorityId) {
                    ForEach(0 ..< 2) {
                        Text("Priority \($0)")
                    }
                }
                Picker("Call type", selection: $callTypeId) {
                    ForEach(0 ..< 3) {
                        Text("Call type \($0)")
                    }
                }
            }

            Section {

                Toggle(isOn: $outOfChemicals) {
                    Text("Out of chemicals")
                }
                Toggle(isOn: $isReturnCall) {
                    Text("Is return call")
                }
            }
        }
    }
}

struct CreateDispatchView_Previews: PreviewProvider {
    static var previews: some View {
        CreateDispatchView()
    }
}

swift

swiftui

回答 1

Stack Overflow用户

回答已采纳

发布于 2019-10-17 14:10:17

大型嵌套ViewBuilder表达式的处理是当前swift编译器中的一个弱点。不过，一般来说，它建议“尝试将表达式拆分成不同的子部分”是一个很好的建议:将这些整体ViewBuilder表达式重构为单独的动态变量是提高性能的好方法(此外，它还有助于隔离实际错误)。

下面是一个如何重构代码以成功编译的示例：

struct CreateDispatchView: View {
    @State private var customerId: Int = 0
    @State private var name: String = ""
    @State private var phone: String = ""
    @State private var description: String = ""
    @State private var priorityId: Int = 0
    @State private var callTypeId: Int = 0
    @State private var bay: String = ""
    @State private var poTicket: String = ""
    @State private var outOfChemicals: Bool = false
    @State private var isReturnCall: Bool = false

    var body: some View {
        Form {
            customerSection
            prioritySection
            infoSection
        }
    }

    private var customerSection: some View {
        Section {
            Picker("Customer", selection: $customerId) {
                ForEach(0 ..< 10) {
                    Text("Customer \($0)")
                }
            }
            TextField("Name", text: $name)
            TextField("Phone", text: $phone)
            TextField("Description", text: $description)
            TextField("Bay", text: $bay)
            TextField("PO ticket", text: $poTicket)
        }
    }

    private var prioritySection: some View {
        Section {
            Picker("Priority", selection: $priorityId) {
                ForEach(0 ..< 2) {
                    Text("Priority \($0)")
                }
            }
            Picker("Call type", selection: $callTypeId) {
                ForEach(0 ..< 3) {
                    Text("Call type \($0)")
                }
            }
        }
    }

    private var infoSection: some View {
        Section {
            Toggle(isOn: $outOfChemicals) {
                Text("Out of chemicals")
            }
            Toggle(isOn: $isReturnCall) {
                Text("Is return call")
            }
        }
    }
}