Newbie (faq!): pmw/tkinter menubar command-option

[Brian Elmegaard]

Martin Rand wrote:

Thanks for the answer.
I am not sure, I understand fully what you mean. So, please let me ask
again.

> 
> When you assign to the 'command' argument, you need to pass a
> *reference* to a function; but what you are doing is passing the
> result of *invoking* the function when you construct the menu. In this
> example the function doesn't return a result, so 'command' gets
> assigned 'None' in each case. (And so never tries to do anything for
> the callback.)
> 
I think I get this.

> Since in this artificial example (and some real-life ones) you may
> want to pass a parameter to a common function, you can construct an
> anonymous "wrapper" function to look after the specific parameter
> generation, using a lambda expression. For instance:
> 
> filemenu.add_command(label="New", command=lambda: callback('new'))
> 

Ok, this works. What I want to make is a canvas, where I may put
different figures on by invoking functions. This doesn't seem to work as
you described, however.

What I have is a class Demo, where the canvas and menu is created in
__init__ and assignments as:
        self.Canvas=Canvas
        self.canvas=Canvas.component('canvas')
are done.

A menu is created with an entry like:
        menuBar.addmenuitem('ComponentList','command',
                            label='Round Thing',
                            command=self.addComponent(150,30))

where addComponent says:
    def addComponent(self,x,y):
	width = 10 
	height = 10 
	self.canvas.create_oval(
	    x - width, y - height, x + width, y + height)

It is defined inside the class. This puts a circle on the canvas during
initialization, but probably for the same reason as explained above, it
is assigned the same None, and must be changed. But, to what?


Brian