SwiftUI 函数显示 "Modifying state during view update, this will cause undefined behavior."

Question

该代码的工作原理在于它会像我想要的那样调出 5 个随机辅音和 2 个元音，但它显示一条警告消息“在视图更新期间修改状态，这将导致未定义的行为。”

我是 Swift 的新手，当我搜索 swiftui 和“在视图更新期间修改状态，这将导致未定义的行为”时，我不明白我在网上阅读的答案。至少我不太了解修复我自己的代码。我离弄清楚如何修改我的代码以消除警告还差得很远。请帮忙

仅供参考 - 我想将我的元音和辅音保存在（排序的）数组中，当按下按钮以滚动新的随机元音和辅音时更新这些数组。

import SwiftUI

struct ContentView: View {
  @State private var vowels = ["X","X"]
  @State private var consonants = ["X","X","X","X","X"]
  
  var body: some View {
    VStack {
      Spacer()
      Text(rollConsonants())
      Text(rollVowels())
      Spacer()
      Button("Reroll") {
        _ = rollVowels()
        _ = rollConsonants()
      }
    }
    .font(.largeTitle)
  }
  
  
  func rollVowels() -> String {
    vowels = ["A","E","I","O","U"].shuffled().prefix(2).sorted()   // message here
    let string = vowels.joined(separator:"   ")
    return string
  }
  
  func rollConsonants() -> String {
    let commonConsonants = ["C","D","L","N","R","S","T"].shuffled().prefix(2)
    var otherConsonants = ["B","F","G","H","K","M","P","V","W","Y","*"].shuffled().prefix(3)
    let rareConsonants = ["J","Q","X","Z"].shuffled()
    if let i = otherConsonants.firstIndex(of: "*") {
      otherConsonants[i] = rareConsonants[0]
    }
    consonants = (commonConsonants + otherConsonants).sorted()   // message here
    let string = consonants.joined(separator:"   ")
    return string
  }

  
}

Answer 1

是因为：

Text(rollConsonants())
Text(rollVowels())

您正在修改状态，而 SwiftUI 正在尝试呈现文本。

此更改通过将更新状态的行为与读取状态的行为分开来修复警告：

import SwiftUI

struct ContentView: View {
    @State private var vowels = ["X", "X"]
    @State private var consonants = ["X", "X", "X", "X", "X"]

    var formattedVowels: String {
        vowels.joined(separator: "   ")
    }

    var formattedConsonants: String {
        consonants.joined(separator: "   ")
    }

    var body: some View {
        VStack {
            Spacer()
            Text(formattedConsonants)
            Text(formattedVowels)
            Spacer()
            Button("Reroll") {
                rollVowels()
                rollConsonants()
            }
        }
        .font(.largeTitle)
    }

    func rollVowels() {
        vowels = ["A", "E", "I", "O", "U"].shuffled().prefix(2).sorted() // message here
    }

    func rollConsonants() {
        let commonConsonants = ["C", "D", "L", "N", "R", "S", "T"].shuffled().prefix(2)
        var otherConsonants = ["B", "F", "G", "H", "K", "M", "P", "V", "W", "Y", "*"].shuffled().prefix(3)
        let rareConsonants = ["J", "Q", "X", "Z"].shuffled()
        if let i = otherConsonants.firstIndex(of: "*") {
            otherConsonants[i] = rareConsonants[0]
        }
        consonants = (commonConsonants + otherConsonants).sorted() // message here
    }
}

SwiftUI 函数显示 "Modifying state during view update, this will cause undefined behavior."

SwiftUI function shows "Modifying state during view update, this will cause undefined behavior."

swift

swiftui

warnings

swift5

swiftui-view