macOS: Take Emoji from CharacterPalette (revised)

The emoji picker needs a minimal implementation of NSTextInputClient. For example a button:

class MyButton: NSButton, NSTextInputClient {
    
    override var acceptsFirstResponder: Bool {
        get {
            return true
        }
    }
    
    override func becomeFirstResponder() -> Bool {
        return true
    }
    
    override func resignFirstResponder() -> Bool {
        return true
    }

    func insertText(_ string: Any, replacementRange: NSRange) {
        // this method is called when the user selects an emoji
        if let string = string as? String {
            self.title = string
        }
    }
    
    func setMarkedText(_ string: Any, selectedRange: NSRange, replacementRange: NSRange) {
    }
    
    func unmarkText() {
    }
    
    func selectedRange() -> NSRange {
        return NSMakeRange(0, 0)
    }
    
    func markedRange() -> NSRange {
        return NSMakeRange(NSNotFound, 0)
    }
    
    func hasMarkedText() -> Bool {
        return false
    }
    
    func attributedSubstring(forProposedRange range: NSRange, actualRange: NSRangePointer?) -> NSAttributedString? {
        return nil
    }
    
    func validAttributesForMarkedText() -> [NSAttributedString.Key] {
        return []
    }
    
    func firstRect(forCharacterRange range: NSRange, actualRange: NSRangePointer?) -> NSRect {
        // the emoji picker uses the returned rect to position itself
        var rect = self.bounds
        rect.origin.x = NSMidX(rect)
        rect.size.width = 0
        return self.window!.convertToScreen(self.convert(rect, to:nil))
    }
    
    func characterIndex(for point: NSPoint) -> Int {
        return 0
    }
    
}

NSTextInputClient needs a NSTextInputContext. NSView returns a context from inputContext if the class conforms to NSTextInputClient unless isEditable is implemented and returns false. A label doesn't return a NSTextInputContext, the solution is to override inputContext:

class MyTextField: NSTextField, NSTextInputClient {
    
    var myInputContext : NSTextInputContext?

    override var inputContext: NSTextInputContext? {
        get {
            if myInputContext == nil {
                myInputContext = NSTextInputContext(client:self)
            }
            return myInputContext
        }
    }

    // and the same methods as the button, set self.stringValue instead of self.title in insertText(_:replacementRange:)

 }

Willeke pointed me at NSTextInputClient which has provided the best solution so far. Apple's only example is in ObjectiveC, convoluted, and overly complex for what I was trying to do, so I am reproducing my code here.

Caveat: this is not a full implementation of NSTextInputClient, just enough to capture emoji input

I have created an NSButton subclass:

class TextReceiverButton: NSButton, NSTextInputClient {
    //specific methods
    func setButtonTitle(_ string: String?){
        self.title = string ??  
    }

//NSTextInputClient methods    

    func insertText(_ string: Any, replacementRange: NSRange) {
       let receivedText = string as? String
       setButtonTitle(receivedText)
    }
    

    func validAttributesForMarkedText() -> [NSAttributedString.Key] {
        return [.font, .paragraphStyle, .writingDirection] 
    }

//Omitted: For anything else that wants a value, I return NSMakeRange(0, 0)/NSRect.zero or 0 as well as false for marked text and nil for attributed substring
    }

(If you add the protocol to your class, it will offer stubs for the other methods)

The full set for NSAttributedString.Key is

[.font, .foregroundColor, .glyphInfo, .kern, .ligature, .link, .markedClauseSegment, .obliqueness, .paragraphStyle, .shadow, .spellingState,  .strikethroughColor, .strikethroughStyle, .strokeColor, .strokeWidth, .superscript, .textAlternatives, .textEffect, .toolTip, .underlineColor, .underlineStyle, .verticalGlyphForm, .writingDirection]

(I have tested the short form with simple and composite emoji and nothing else seems necessary.)

The button's action is

@IBAction func displayEmojiInButton(_ sender: Any) {
    NSApp.orderFrontCharacterPalette(self)
view.window?.makeFirstResponder(textReceiverButton)
}

Problems/Bugs

The NSTextInputClient document says 'you can subclass NSView' and Apple's code turns an NSView into a fully functional (receiving and drawing) text view class (I can't built it, but I assume it worked). So theoretically, you should be able to use the same code for NSTextField, which also ultimately inherits from NSView.

However, it turns out that NSTextField displays the 'CharacterPalette allegedly opens but never displays' bug I talked about earlier; though it does work with NSView. (I have not tested this further). Furthermore, NSTextInputClient is not a complete replacement for NSTextView: it does not receive input from the keyboard viewer. (See Willecke's answer/comment for explanation/solution to these).

Verdict

NSApp.orderFrontCharacterPalette(self) fails 95% of the time when called from a view in the vincinity of a tab view (in splitView next to TabViewController, embedded in TabViewController), so while this code may be correct, it's also useless a lot of the time, at least under 10.13.