SwiftUI：如何将焦点定位在非空TextField的文本末尾？

我有一个TextField，有时会预先填充一段文本供用户补充完整。我用FocusState布尔变量在视图出现时让该字段获得焦点，希望光标能落在预填充文本的末尾，方便用户接着输入。但现在视图出现时，预填充的整个文本会被选中，用户一输入就会覆盖原有内容，请问有没有办法把光标定位到预填充文本的末尾？

代码片段 #

struct MyView: View {
    @State var myText: String = ""
    @FocusState private var isFocused: Bool
    
    var body: some View {
        TextField("Enter text...", text: $myText)
            .font(.largeTitle)
            .multilineTextAlignment(.center)
            .focused($isFocused)
            .onAppear {
                isFocused = true
                myText = "text to be completed"
            }
    }
}

当前效果 #

期望效果 #

SwiftUI原生TextField没有直接控制光标位置的API，你可以通过两种方式解决这个问题：

方法一：调整顺序+异步调度 #

先设置预填充文本，再异步设置焦点，避免TextField在文本更新时自动选中全部内容：

struct MyView: View {
    @State var myText: String = ""
    @FocusState private var isFocused: Bool
    
    var body: some View {
        TextField("Enter text...", text: $myText)
            .font(.largeTitle)
            .multilineTextAlignment(.center)
            .focused($isFocused)
            .onAppear {
                myText = "text to be completed"
                // 异步设置焦点，等文本渲染完成再聚焦
                DispatchQueue.main.async {
                    isFocused = true
                }
            }
    }
}

这个方法简单快捷，但在复杂视图层级下可能不稳定，如果遇到问题可以用下面的方法。

方法二：自定义TextField（基于UIKit） #

通过包装UITextField，能精确控制光标位置，稳定性更高：

struct CustomTextField: UIViewRepresentable {
    @Binding var text: String
    @Binding var isFocused: Bool
    var placeholder: String
    
    func makeUIView(context: Context) -> UITextField {
        let textField = UITextField()
        textField.placeholder = placeholder
        textField.font = UIFont.systemFont(ofSize: 34) // 对应SwiftUI的.largeTitle
        textField.textAlignment = .center
        textField.delegate = context.coordinator
        return textField
    }
    
    func updateUIView(_ uiView: UITextField, context: Context) {
        uiView.text = text
        
        // 聚焦时把光标移到文本末尾
        if isFocused {
            uiView.becomeFirstResponder()
            let endPosition = uiView.endOfDocument
            uiView.selectedTextRange = uiView.textRange(from: endPosition, to: endPosition)
        } else {
            uiView.resignFirstResponder()
        }
    }
    
    func makeCoordinator() -> Coordinator {
        Coordinator(parent: self)
    }
    
    class Coordinator: NSObject, UITextFieldDelegate {
        var parent: CustomTextField
        
        init(parent: CustomTextField) {
            self.parent = parent
        }
        
        func textFieldDidChangeSelection(_ textField: UITextField) {
            parent.text = textField.text ?? ""
        }
        
        func textFieldDidEndEditing(_ textField: UITextField) {
            parent.isFocused = false
        }
    }
}

// 使用示例
struct MyView: View {
    @State var myText: String = ""
    @State private var isFocused: Bool = false
    
    var body: some View {
        CustomTextField(text: $myText, isFocused: $isFocused, placeholder: "Enter text...")
            .onAppear {
                myText = "text to be completed"
                isFocused = true
            }
    }
}

这个方法能完全控制TextField的光标行为，适合需要精确控制的场景。

内容的提问来源于stack exchange，提问作者Simon W