TIL: How to Make NSTextView Reject Newlines

Today I learned that a NSWindow’s field editor cannot trivially be set to “single line mode.” A field editor is a NSText subclass like NSTextView, but NSTextField is only a configurable widget that uses the field editor.

How does the “single line mode” setting do what it does? I have no clue.

So how do you make custom field editor classes reject newlines both through pressing return, alt-return, and pasting text with newline characters? You override its NSResponder hooks!

class CustomFieldEditor: NSTextView {

    // ... imagine some relevant customizations here ...
    
    override func insertNewline(sender: AnyObject?) {

        // consume and discard
    }

    override func insertNewlineIgnoringFieldEditor(sender: AnyObject?) {

        // consume and discard
    }

    override func paste(sender: AnyObject?) {

        let pasteboard = NSPasteboard.generalPasteboard()

        guard let pasteboardItem = pasteboard.pasteboardItems?.first,
            text = pasteboardItem.stringForType(ContentTypes.text)
            else { return }

        let cleanText = text.stringByReplacingOccurrencesOfString("\n", withString: " ")

        self.insertText(cleanText)
    }
}

enum ContentTypes {
    static let text = "public.utf8-plain-text"
}

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