SwiftUI macOS Big Sur环境下应用启动时如何自动聚焦TextEditor

兼容 macOS Big Sur （11.x）方案 #

Big Sur 版本下 SwiftUI 未提供原生聚焦控制API，需通过桥接 AppKit 实现自动聚焦，无需复杂自定义代码，可按以下步骤实现：

1. 实现可自动聚焦的TextEditor包装组件：

struct FocusableTextEditor: NSViewRepresentable {
    @Binding var text: String
    var isFirstResponder: Bool = false

    func makeNSView(context: Context) -> NSTextView {
        let textView = NSTextView()
        textView.string = text
        return textView
    }

    func updateNSView(_ nsView: NSTextView, context: Context) {
        nsView.string = text
        if isFirstResponder, nsView.window != nil, !nsView.isFirstResponder {
            DispatchQueue.main.async {
                nsView.window?.makeFirstResponder(nsView)
            }
        }
    }
}

2. 在你的MailView中替换原生TextEditor，并在视图出现时触发聚焦：

struct MailView: View {
    let mail: Mail
    @State private var fullText: String = "This is some editable text..."
    @State private var editorShouldFocus = false

    var body: some View {
        VStack(alignment: .leading) {
            FocusableTextEditor(text: $fullText, isFirstResponder: editorShouldFocus)
        }
        .onAppear {
            editorShouldFocus = true
        }
    }
}

3. 应用启动时默认选中第一个条目后，右侧MailView加载时会自动触发onAppear，完成TextEditor的自动聚焦。

若首次启动偶现聚焦失败，可将makeFirstResponder的调用逻辑增加0.1秒延迟，抵消三栏布局的视图渲染耗时：

DispatchQueue.main.asyncAfter(deadline: .now() + 0.1) {
    nsView.window?.makeFirstResponder(nsView)
}

macOS Monterey 及以上（12.0+）原生方案 #

更高版本系统可直接使用FocusState原生API实现，代码更简洁：

struct MailView: View {
    let mail: Mail
    @State private var fullText: String = "This is some editable text..."
    @FocusState private var isEditorFocused: Bool

    var body: some View {
        VStack(alignment: .leading) {
            TextEditor(text: $fullText)
                .focused($isEditorFocused)
        }
        .onAppear {
            isEditorFocused = true
        }
    }
}

内容的提问来源于stack exchange，提问作者Aleph