How do I use KeyPressFcn? How do I time the space bar press?

I don't understand how to use the KeyPressFcn. I'm not making a GUI. I'm using an image on an axis. This is the relevant code:

imshow(imscreen);
imscreen = gcf;
a = 1;
set(gcf, 'KeyPressFcn', 'a = get(gcf, ''CurrentCharacter'')');
a = double(a);
*and this is where I set the conditions for x values (trying to move the ball horizontally):*
if a == 28
    xclick = x2 - 2;
elseif a == 29
    disp('Right')
    xclick = x2 + 2;
end

and then I set the ball to the new xclick value. This doesn't seem to work. What should I do?

Answer 1

[Walter Roberson]

When you use a string as a callback, the string is executed in the context of the base workspace.

You need to set the KeyPressFcn to be the handle of a function that will test the key and perform the appropriate action. Or you need to switch to one of the File Exchange contributions such as GetKey or GetKeyWait