删除行时SwiftUI ForEach索引超出范围错误 [英] SwiftUI ForEach index out of range error when removing row

问题描述

我有一个 ForEach 块和一个 Stepper 嵌入在 List 视图中.List 视图第一部分的内容如下:

I have a ForEach block and a Stepper embedded in a List view. The contents of the List view's first section is as follows:

ForEach(record.nodes.indices, id: .self) { index in
    HStack {
        TextField("X", text: self.$record.nodes[index].xString)
        Spacer()
        Divider()
        TextField("Y", text: self.$record.nodes[index].yString)
        Spacer()
    }
}
Stepper("± node", onIncrement: {
    self.record.nodes.append(Node(x: 0, y: 0))
}, onDecrement: {
    self.record.nodes.removeLast()
})

我面临的问题是，在调用 self.record.nodes.removeLast() 时，应用程序因 Index out of range 错误而崩溃.我一直试图解决这个问题几个小时，但无济于事.

The issue I am facing is that upon calling self.record.nodes.removeLast(), the application crashes with an Index out of range error. I've been trying to solve this for hours, but to no avail.

我最初使用了 onDelete，但是这产生了同样的问题.

I originally used onDelete, however that produced the same issue.

该项目可以在 https://github.com/jacobcxdev/Timekeeper 找到，带有这个Record.swift.

The project can be found at https://github.com/jacobcxdev/Timekeeper, with this error happening in RecordDetailView.swift.

推荐答案

问题描述

索引超出范围错误是因为init(_ data: Range, content: @escaping (Int) -> Content) ForEach 的初始化器不允许我们动态修改数组.为此，我们需要使用 init(_ data: Data, content: @escaping (Data.Element) -> Content) 初始值设定项，如 评论.但是，正如@JacobCXDev 在回复中澄清的那样，它在嵌套绑定的这种情况下也不起作用.

Problem Description

The index out of range error occurs because init(_ data: Range<Int>, content: @escaping (Int) -> Content) initializer of ForEach does not allow us to modify the array dynamically. For that, we need to use init(_ data: Data, content: @escaping (Data.Element) -> Content) initializer as @Asperi explained in the comment. However, it does not work either in this situation, where bindings are nested, as @JacobCXDev clarified in the reply.

使用自定义绑定和附加状态.自定义绑定解决了嵌套绑定上的 ForEach 问题.最重要的是，您需要在每次触摸自定义绑定后修改状态以重新渲染屏幕.以下是一个简化的(未经测试的)代码示例.

Use custom bindings and an additional state. The custom bindings solve the issue of ForEach over nested bindings. On top of that, you need to modify a state after every touch on the custom binding to re-render the screen. The following is a simplified (untested) code sample.

@State private var xString: String

---

ForEach(record.nodes) { node in
    let xStringBinding = Binding(
        get: { node.xString },
        set: {
            node.xString = $0
            self.xString = $0
        }
    )
    TextField("X", text: xStringBinding)
}

解决方案(2020 年 7 月 10 日添加)

只需为子项定义一个视图结构，如下所示.

Solution (added on July 10, 2020)

Just define a view struct for the children like the following.

ForEach(record.nodes) { node in
    NodeView(node: node)
}

---

struct NodeView: View {
    @ObservedObject var node: Node

    var body: some View {
        TextField("X", text: self.$node.xString)
    }
}

class Node: ObservableObject, Identifiable {
    @Published var xString: String
    let id: String = UUID().uuidString

    init(xString: String) {
        self.xString = xString
    }
}

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