'不能在不可变值上使用可变 getter:'self' 在迭代时是不可变的? [英] 'Cannot use mutating getter on immutable value: 'self' is immutable' when iterating?

问题描述

有谁知道为什么 ForEach 中的 self.indexCount 会给出错误 Cannot use mutating getter on immutable value: 'self' is immutable错误?我可以提供 aView 和 indexCount，但不是很方便.我没有改变 indexCount.这是 SwiftUI 错误还是故意的?

Does anyone know why the self.indexCount in the ForEach is giving the error Cannot use mutating getter on immutable value: 'self' is immutable error? I can provide aView with indexCount, but it's not very convenient. I'm not changing indexCount. Is this a SwiftUI bug or intentional?

struct aView: View {
    let array: [[String]]
    lazy var indexCount: Int = array[0].count

    var body: some View {
        VStack {
            ForEach(0..<self.indexCount, id: \.self) { index in
                Text("Hello World")
           }
        }
    }
}

推荐答案

这是故意的.在 SwiftUI 中，只有 @State 变量可以更改.你不能像那样使用 lazy var.用计算属性替换它:

It's intentional. In SwiftUI, only @State variables can change. You can't use a lazy var like that. Replace it with a computed property:

var indexCount : Int { array[0].count }

无论如何这更好，因为它总是正确的:indexCount 将始终是 array[0] 的 current 大小)，而您的方式，无论count是第一次获取时，该值都会冻结.

That's better anyway, because it will always be correct: indexCount will always be the current size of array[0]), whereas your way, the value will freeze at whatever the count is the first time it is fetched.

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