您应该使用自定义Formatter或onCommit处理程序。令人讨厌的是，这些内容不会在您键入时应用，而仅在您提交编辑时才应用

Formatter示例：

final class CapitalizedFormatter: Formatter {
  override func string(for obj: Any?) -> String? {
    guard let string = obj as? String else {
      return ""
    }
    return string.uppercased()
  }

  override func getObjectValue(_ obj: AutoreleasingUnsafeMutablePointer<AnyObject?>?,for string: String,errorDescription error: AutoreleasingUnsafeMutablePointer<NSString?>?) -> Bool {
    obj?.pointee = string as NSString
    return true
  }
}

struct ContentView: View {
  @State var capitalizedText: String = ""
  var body: some View {
    TextField(
      "placeholder",value: $capitalizedText,formatter: CapitalizedFormatter()
    )
  }
}

onCommit示例：

struct ContentView: View {
  @State var capitalizedText: String = ""
  var body: some View {
    TextField(
      "Placeholder",text: $capitalizedText,onCommit: { self.capitalizedText = self.capitalizedText.uppercased() }
    )
  }
}

如果您想要连续的文本值，则使用绑定在设置程序中拦截新值，然后格式化它们，然后在getter中发出该值：

final class Model: ObservableObject {
  @Published var capitalizedText = ""
  func set(text: String) {
    capitalizedText = text.uppercased()
  }
}

struct ContentView: View {
  @ObservedObject var model: Model
  var textBinding: Binding<String>
  init() {
    let model = Model()
    self.textBinding = .init(
      get: { model.capitalizedText },set: { model.set(text: $0) }
    )
    self.model = model
  }

  var body: some View {
    TextField(
      "Placeholder",text: textBinding
    )
  }
}