SwiftUI，如果在里面查看 [英] SwiftUI if let inside View

问题描述

我想要在View内使用if let语句.

I want a if let statement inside a View.

@ObservedObject var person: Person?
 var body: some View {
      if person != nil {
        // this works
      }
      if let p = person {
        // Compiler error
      }
    }

包含封闭流的控制流语句不能与函数构建器"ViewBuilder"一起使用

推荐答案

或者您可以创建自己的IfLet视图构建器:

Or you can create your own IfLet view builder:

import SwiftUI

struct IfLet<Value, Content, NilContent>: View where Content: View, NilContent: View {

    let value: Value?
    let contentBuilder: (Value) -> Content
    let nilContentBuilder: () -> NilContent

    init(_ optionalValue: Value?, @ViewBuilder whenPresent contentBuilder: @escaping (Value) -> Content, @ViewBuilder whenNil nilContentBuilder: @escaping () -> NilContent) {
        self.value = optionalValue
        self.contentBuilder = contentBuilder
        self.nilContentBuilder = nilContentBuilder
    }

    var body: some View {
        Group {
            if value != nil {
                contentBuilder(value!)
            } else {
                nilContentBuilder()
            }
        }
    }
}

extension IfLet where NilContent == EmptyView {

    init(_ optionalValue: Value?, @ViewBuilder whenPresent contentBuilder: @escaping (Value) -> Content) {
        self.init(optionalValue, whenPresent: contentBuilder, whenNil: { EmptyView() })
    }
}

现在，您可以执行以下操作:

Using this, you can now do the following:

var body: some View {
    IfLet(pieceOfData) { realData in
        // realData is no longer optional
    }
}

是否要回答，如果您的可选选项是nil?

Want to respond if your optional is nil?

var body: some View {
    IfLet(pieceOfData, whenPresent: { realData in
        // realData is no longer optional
        DataView(realData)
    }, whenNil: {
        EmptyDataView()
    })
}

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