在 SwiftUI 中为 TextField 添加前缀 [英] Add a prefix to TextField in SwiftUI

问题描述

我想在 文本字段 中添加一个无法擦除的+"号.用户应该能够在它之后输入值，如果他按下退格键，它应该只擦除他输入的值.当我输入任何其他数字时，它会自动在输入值的开头添加一个+".

I want a ‘+’ Sign in the Textfield which cannot be erased. A user should be able to enter values after it and if he presses backspace it should only erase the value he entered. And when I write any other number it will automatically add a ‘+’ at the beginning of the enter value.

例如:-我想在文本字段中添加国家/地区代码，因此，只要用户开始输入，+"就会自动添加到字段的开头国家代码.

For Example:- I want to add country code in the textfield so, '+' automatically add in the beginning of the field as soon as user start typing a country code.

推荐答案

在 SwiftUI 中，您可能希望使用 Combine 框架来执行此操作.创建一个 ObservableObject 来处理值的变化.示例代码在这里:

In SwiftUI, you may want to use Combine framework to do this. Create an ObservableObject to handle value changes. Example code here:

import SwiftUI
import Combine

struct ContentView: View {

    class ViewModel: ObservableObject {
        @Published var text = "" {
            didSet {
                if text.prefix(1) != "+" {
                    text = "+" + text
                }
            }
        }
    }

    @ObservedObject var viewModel = ViewModel()

    var body: some View {
        TextField("Placeholder", text:$viewModel.text)
    }
}

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