How do I implement a selection in a focus mode extension?

To implement a selection in a focus mode extension, you can leverage the new capabilities in SwiftUI and AppKit as discussed in the WWDC sessions.

SwiftUI

In SwiftUI, you can manage text selection programmatically within text editing controls. This allows you to read properties of the selection, such as the selected ranges, and use this information to provide features like suggested completions or rhymes.

For example, you can use a binding to update the selection and read the selected text:

@State private var selectedText: String = ""
@State private var text: String = "Your editable text here"

var body: some View {
    TextEditor(text: $text)
        .onChange(of: text) { newValue in
            // Update selectedText based on the new selection
        }
}

You can also programmatically drive the focus state of a search field and add text suggestions:

@State private var searchTerm: String = ""
@FocusState private var isSearchFieldFocused: Bool

var body: some View {
    TextField("Search", text: $searchTerm)
        .focused($isSearchFieldFocused)
        .onChange(of: searchTerm) { newValue in
            // Provide suggestions based on the search term
        }
}

For more details, you can refer to the session What’s new in SwiftUI.

AppKit

In AppKit, you can implement the NSViewContentSelectionInfo protocol to provide geometry information about the selection, which helps in positioning context menus appropriately near the selection.

Here's a brief example of how you might implement this:

class CustomView: NSView, NSViewContentSelectionInfo {
    var selectedRange: NSRange = NSRange(location: 0, length: 0)

    func selectionRects(for range: NSRange) -> [NSValue] {
        // Return an array of NSValue objects representing the selection rects
    }

    func selectionBounds(for range: NSRange) -> NSRect {
        // Return the bounding rect for the selection
    }
}

For more details, you can refer to the session What’s new in AppKit.

Relevant Sessions

1. What’s new in SwiftUI
2. What’s new in AppKit

These sessions provide comprehensive insights into managing text selection and focus states in both SwiftUI and AppKit.