Yeah, I’m getting intimate with Cocoa development, so you can expect occasional posts like this one. My readers are not supposed to care about this; I’m just posting it because I’ve been googling that question for an hour and didn’t find a proper answer anywhere.

There’s a point in the Cocoa documentation (I would link to it, but it looks like URLs tend to change every so often) that says:

A text field allows you to set the attributes of its text, the text background color, whether it draws the background, and whether it draws a bezel or border around its text. Note that the text and background colors of selected text are configurable. The selected text color overrides any actual text color applied to the text while it’s selected (this is generally the case with controls).

But nowhere does it say how. NSTextView has a setSelectedTextAttributes, but NSTextField doesn’t; so how do you change the selected text’s attributes?

Maybe you’re supposed to know that from the start (I’m learning Cocoa in random order, by googling for bits of information as I need them, and I know that’s not how you’re supposed to do it but, hey, my app works, and it doesn’t even seem to leak), but NSTextView isn’t just a control you can drop in Interface Builder to let users enter long, formatted text; there’s also an NSTextView associated with each window, and it processes the text behind the scenes or something.

So all you have to do is get access to that NSTextView, and setSelectedTextAttributes on it. Here’s how you get text fields of the window InputWindow to show selected text on a black background:

The (NSTextView*) bit is because fieldEditor:forObject: thinks it returns an NSText*, even though it seems like it does return an NSTextView* — otherwise the code just wouldn’t work, would it? Looks like a known bug in the Cocoa headers.