Can't bind KeyPress event to Canvas

[dmaggian]

I can't seem to bind key press events to the canvas widget.I used the wish shell for the simplest possible test and wrote the following code from the console.

(bin) 2 % canvas .can -bg black
.can
(bin) 3 % pack .can
(bin) 4 % bind .can <Button-1> {tk_messageBox -message "%W got button press"}
(bin) 5 % bind .can <KeyPress> {tk_messageBox -message "%W got key press"}

When I click the mouse button inside the canvas I get the message expected but when I press a key inside the canvas nothing happens. Anyone else have this problem?

 

[Bong]

I looked into this once before and I recall having convinced myself that keypress didn't make any sense for canvas widgets. There is no relationship between the keyboard and the canvas. Now, if you put a textbox on the canvas, you could probably bind keypress to that.

_________________
Bob Rashkin

 

[dmaggian]

Hmmm... I can think of lot's of reasons to bind keys to a canvas widget. For example, in the drawing program I'm working on right now I have the ability to select objects to be moved or deleted, I'd like to end the selection by hitting the Escape key, once the objects are selected, I might like to hit them with the Delete key. I'm not using an text, just graphics types primitives.

For now, I'm doing a bind all which allows me to use the escape key inside the canvas (or from anywhere else) but this solution is not ideal; I might want the same key to do something else in other windows.

 

[dmaggian]

The response I got from Jeff Hobbs on this issue is documented below; This fixes the problem.

This is a classic problem with a few widgets in Tk. The widget has to have *focus* to receive key input. What you can do is:

bind Canvas <ButtonPress-1> {+; focus %W}

to force focus always into canvases, or you can just explicitly set focus some other way.