如何使用 Combine 来跟踪 UIViewRepresentable 类中的 UITextField 更改？

Question

我创建了一个自定义文本字段，我想利用结合。为了在文本字段中的文本更改时收到通知，我目前使用自定义修饰符。它运行良好，但我希望此代码可以在我的 CustomTextField 结构中。

我的 CustomTextField 结构符合 UIViewRepresentable。在这个结构体中，有一个名为 Coordinator 的 NSObject 类，它符合 UITextFieldDelegate。

我已经在使用其他 UITextField 委托方法，但找不到完全符合我使用自定义修饰符所做的工作的方法。有些方法很接近，但并不完全按照我希望的方式行事。无论如何，我觉得最好将这个新的自定义 textFieldDidChange 方法放在 Coordinator 类中。

这是我的自定义修饰符

private let textFieldDidChange = NotificationCenter.default
    .publisher(for: UITextField.textDidChangeNotification)
    .map { $0.object as! UITextField}


struct CustomModifer: ViewModifier {

     func body(content: Content) -> some View {
         content
             .tag(1)
             .onReceive(textFieldDidChange) { data in

                //do something

             }
    }
}

我的 CustomTextField 用于 SwiftUI 视图，并附加了我的自定义修饰符。当文本字段发生变化时，我可以做一些事情。修改器也使用Combine。它工作得很好，但我不希望此功能采用修饰符的形式。我想在我的 Coordinator 类中使用它，以及我的 UITextFieldDelegate 方法。

这是我的 CustomTextField

struct CustomTextField: UIViewRepresentable {

    var isFirstResponder: Bool = false
    @EnvironmentObject var authenticationViewModel: AuthenticationViewModel

    func makeCoordinator() -> Coordinator {
        return Coordinator(authenticationViewModel: self._authenticationViewModel)
    }

    class Coordinator: NSObject, UITextFieldDelegate {

        var didBecomeFirstResponder = false
        @EnvironmentObject var authenticationViewModel: AuthenticationViewModel

        init(authenticationViewModel: EnvironmentObject<AuthenticationViewModel>)
        {
            self._authenticationViewModel = authenticationViewModel
        }

        // Limit the amount of characters that can be typed in the field
        func textField(_ textField: UITextField, shouldChangeCharactersIn range: NSRange, replacementString string: String) -> Bool {

            let currentText = textField.text ?? ""
            guard let stringRange = Range(range, in: currentText) else { return false }
            let updatedText = currentText.replacingCharacters(in: stringRange, with: string)
            return updatedText.count <= 14
        }

        /* I want to put my textFieldDidChange method right here */

        /* * * * * * * * * * * * * * * * * * * * * * * * * * * * */


        func textFieldDidEndEditing(_ textField: UITextField) {

            textField.resignFirstResponder()
            textField.endEditing(true)
        }

    }

    func makeUIView(context: Context) -> UITextField {

        let textField = UITextField()
        textField.delegate = context.coordinator
        textField.placeholder = context.coordinator.authenticationViewModel.placeholder
        textField.font = .systemFont(ofSize: 33, weight: .bold)
        textField.keyboardType = .numberPad

        return textField
    }

    func updateUIView(_ uiView: UITextField, context: Context) {

        let textField = uiView
        textField.text = self.authenticationViewModel.text
    }
}

struct CustomTextField_Previews: PreviewProvider {

    static var previews: some View {
        CustomTextField()
            .previewLayout(.fixed(width: 270, height: 55))
            .previewDisplayName("Custom Textfield")
            .previewDevice(.none)
    }
}

我一直在观看有关 Combine 的视频，我想开始在我正在构建的新应用程序中使用它。我真的认为在这种情况下使用它是正确的，但仍然不太确定如何实现它。我真的很感激一个例子。

总结一下：

我想向我的 Coordinator 类添加一个名为 textFieldDidChange 的函数，并且每次我的文本字段发生更改时都应该触发它。它必须使用Combine。

提前致谢

Answer 1

更新答案

看了你更新的问题后，我意识到我原来的答案可能需要一些清理。我已将模型和协调器合并为一个类，虽然它对我的示例有效，但并不总是可行或可取的。如果模型和协调器不能相同，则不能依赖模型属性的 didSet 方法来更新 textField。因此，相反，我正在使用我们通过@Published模型中的变量免费获得的 Combine 发布者。

我们需要做的关键是：

1. 通过保持model.text和textField.text同步来建立单一的事实来源

   1. 使用@Published属性包装器提供的发布者textField.text在model.text更改时进行更新

   2. 使用.addTarget(:action:for)on 方法在变化时textField更新model.texttextfield.text

2. textDidChange当我们的模型改变时执行一个调用的闭包。

（我更喜欢使用.addTargetfor #1.2 而不是通过NotificationCenter，因为它的代码更少，可以立即工作，并且 UIKit 的用户都知道它）。

这是一个显示此工作的更新示例：

演示

import SwiftUI
import Combine

// Example view showing that `model.text` and `textField.text`
//     stay in sync with one another
struct CustomTextFieldDemo: View {
    @ObservedObject var model = Model()

    var body: some View {
        VStack {
            // The model's text can be used as a property
            Text("The text is \"\(model.text)\"")
            // or as a binding,
            TextField(model.placeholder, text: $model.text)
                .disableAutocorrection(true)
                .padding()
                .border(Color.black)
            // or the model itself can be passed to a CustomTextField
            CustomTextField().environmentObject(model)
                .padding()
                .border(Color.black)
        }
        .frame(height: 100)
        .padding()
    }
}

模型

class Model: ObservableObject {
    @Published var text = ""
    var placeholder = "Placeholder"
}

看法

struct CustomTextField: UIViewRepresentable {
    @EnvironmentObject var model: Model

    func makeCoordinator() -> CustomTextField.Coordinator {
        Coordinator(model: model)
    }

    func makeUIView(context: UIViewRepresentableContext<CustomTextField>) -> UITextField {
        let textField = UITextField()

        // Set the coordinator as the textField's delegate
        textField.delegate = context.coordinator

        // Set up textField's properties
        textField.text = context.coordinator.model.text
        textField.placeholder = context.coordinator.model.placeholder
        textField.autocorrectionType = .no

        // Update model.text when textField.text is changed
        textField.addTarget(context.coordinator,
                            action: #selector(context.coordinator.textFieldDidChange),
                            for: .editingChanged)

        // Update textField.text when model.text is changed
        // The map step is there because .assign(to:on:) complains
        //     if you try to assign a String to textField.text, which is a String?
        // Note that assigning textField.text with .assign(to:on:)
        //     does NOT trigger a UITextField.Event.editingChanged
        let sub = context.coordinator.model.$text.receive(on: RunLoop.main)
                         .map { Optional($0) }
                         .assign(to: \UITextField.text, on: textField)
        context.coordinator.subscribers.append(sub)

        // Become first responder
        textField.becomeFirstResponder()

        return textField
    }

    func updateUIView(_ textField: UITextField, context: UIViewRepresentableContext<CustomTextField>) {
        // If something needs to happen when the view updates
    }
}

视图协调器

extension CustomTextField {
    class Coordinator: NSObject, UITextFieldDelegate, ObservableObject {
        @ObservedObject var model: Model
        var subscribers: [AnyCancellable] = []

        // Make subscriber which runs textDidChange closure whenever model.text changes
        init(model: Model) {
            self.model = model
            let sub = model.$text.receive(on: RunLoop.main).sink(receiveValue: textDidChange)
            subscribers.append(sub)
        }

        // Cancel subscribers when Coordinator is deinitialized
        deinit {
            for sub in subscribers {
                sub.cancel()
            }
        }

        // Any code that needs to be run when model.text changes
        var textDidChange: (String) -> Void = { text in
            print("Text changed to \"\(text)\"")
            // * * * * * * * * * * //
            // Put your code here  //
            // * * * * * * * * * * //
        }

        // Update model.text when textField.text is changed
        @objc func textFieldDidChange(_ textField: UITextField) {
            model.text = textField.text ?? ""
        }

        // Example UITextFieldDelegate method
        func textFieldShouldReturn(_ textField: UITextField) -> Bool {
            textField.resignFirstResponder()
            return true
        }
    }
}

原答案

听起来你有几个目标：

1. 使用 aUITextField以便您可以使用类似的功能.becomeFirstResponder()
2. 文本更改时执行操作
3. 通知其他 SwiftUI 视图文本已更改

我认为您可以使用单个模型类和UIViewRepresentable结构来满足所有这些要求。我以这种方式构建代码的原因是，您有一个单一的事实来源 ( model.text)，它可以与其他采用String或 的SwiftUI 视图互换使用Binding<String>。

模型

class MyTextFieldModel: NSObject, UITextFieldDelegate, ObservableObject {
    // Must be weak, so that we don't have a strong reference cycle
    weak var textField: UITextField?

    // The @Published property wrapper just makes a Combine Publisher for the text
    @Published var text: String = "" {
        // If the model's text property changes, update the UITextField
        didSet {
            textField?.text = text
        }
    }

    // If the UITextField's text property changes, update the model
    @objc func textFieldDidChange() {
        text = textField?.text ?? ""

        // Put your code that needs to run on text change here
        print("Text changed to \"\(text)\"")
    }

    // Example UITextFieldDelegate method
    func textFieldShouldReturn(_ textField: UITextField) -> Bool {
        textField.resignFirstResponder()
        return true
    }
}

看法

struct MyTextField: UIViewRepresentable {
    @ObservedObject var model: MyTextFieldModel

    func makeUIView(context: UIViewRepresentableContext<MyTextField>) -> UITextField {
        let textField = UITextField()

        // Give the model a reference to textField
        model.textField = textField

        // Set the model as the textField's delegate
        textField.delegate = model

        // TextField setup
        textField.text = model.text
        textField.placeholder = "Type in this UITextField"

        // Call the model's textFieldDidChange() method on change
        textField.addTarget(model, action: #selector(model.textFieldDidChange), for: .editingChanged)

        // Become first responder
        textField.becomeFirstResponder()

        return textField
    }

    func updateUIView(_ textField: UITextField, context: UIViewRepresentableContext<MyTextField>) {
        // If something needs to happen when the view updates
    }
}

如果你不需要上面的#3，你可以替换

@ObservedObject var model: MyTextFieldModel

和

@ObservedObject private var model = MyTextFieldModel()

演示

这是显示所有这些工作的演示视图

struct MyTextFieldDemo: View {
    @ObservedObject var model = MyTextFieldModel()

    var body: some View {
        VStack {
            // The model's text can be used as a property
            Text("The text is \"\(model.text)\"")
            // or as a binding,
            TextField("Type in this TextField", text: $model.text)
                .padding()
                .border(Color.black)
            // but the model itself should only be used for one wrapped UITextField
            MyTextField(model: model)
                .padding()
                .border(Color.black)
        }
        .frame(height: 100)
        // Any view can subscribe to the model's text publisher
        .onReceive(model.$text) { text in
                print("I received the text \"\(text)\"")
        }

    }
}