Re: a mouse event problem on macOS

Graham Cox

On 21 Sep 2017, at 3:53 am, James Walker <> wrote:

Thank you very much. Your code didn't work for me at first, perhaps because of a complication that I did not mention in my original message: The original mouse down happens in a Carbon window. Anyway, the mouse events returned by -[NSWindow nextEventMatchingMask:untilDate:inMode:dequeue:] are for the wrong window and hence have the wrong mouse coordinates, so I had to convert the coordinates and create a new NSEvent for the right window before forwarding it on to my view's mouseDragged: method. But it's working now.
OK, sounds a bit smelly, but whatever works, I guess.

The red flag here is the need to “create an event”. I don’t believe there’s ever any reason to do that in mainstream (i.e. app level) code.

NSView has a reference to its window, and the events for that window should have the -locationInWindow coordinate correct for the window. From that you need to convert to the view’s local coordinates using -convertPoint:fromView:, but other than that there’s nothing special to do. I’m not sure why Carbon windows make a difference (surprised they’re still a thing), and since you are creating the overlay window, then everything should be local to that. The original mouse down in the Carbon window is irrelevant in this case - you can simply discard it.

NSView’s trio of mouse methods - mouseDown: -mouseDragged: and -mouseUp: are conveniences - NSView internally implements a loop just like the one I showed which calls out to those methods, but you are not obliged to use them.


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