Tkinter grid layout

Eric Brunel eric_brunel at despammed.com
Wed Jul 6 17:36:01 CEST 2005


On Wed, 06 Jul 2005 11:44:55 +0100, Richard Lewis <richardlewis at fastmail.co.uk> wrote:

> Hi there,
>
> I've got a tree control in Tkinter (using the ESRF Tree module) but I
> can't get it to layout how I want it.
>
> I'd like to have it so that it streches north/south (anchored to the top
> and bottom), is of a fixed width and is anchored to the left hand side.
> Here's my code (its derived from one of the examples from the ESRF web
> site):
>
> class MainWindow(Frame):
[snip code]

First of all, it is not a good idea to make your so-called window inherit from Frame: a Frame is not a window in tk, but a generic container. Creating a Frame without a container window will automatically initialize the tk toolkit, creating a default window which will become the default parent for widgets where you don't specify one. According to the well-known "explicit is better than implicit" principle, if a MainWindow instance are actually the main window for your application, you'd really better inherit from the Tkinter class for the main window, which is Tk. Doing it this way has a lot of advantages over what you do; for example, if you later have to create a menu bar for your application, you will be able to do it in the MainWindow class. If you inherit from Frame, you won't get any access to the actual window, so you won't be able to create a menu in it.

This may seems to be unrelated to your problem, but it's not: by creating a Frame, you introduce one more unneeded container. So, in some code you don't show here, you have to insert the MainWindow instance into its parent window via a call to its pack or grid method. Since the code you show seems to be correct, I guess the problem is in this call to pack or grid, which probably does not tell the Frame how to behave when its parent window is resized, causing it to get the default behaviour, which is "do nothing at all".

To be sure this actually is the problem, try to replace the line:
Frame.__init__(self, master)
in MainWindow.__init__ by:
Frame.__init__(self, master, bg='blue', bd=2)
This way, a blue border will appear around the frame, allowing you to see how it grows.
Then run your application, and resize the window. You should see that the frame does not grow when the window grows, explaining why your tree deos not grow (in fact, it would grow if its container did; but its container doesn't...)

So you should either make your MainWindow class inherit from Tk, which eliminates the unneeded container and the problems it may cause, or make sure the pack or grid on your MainWindow instance actually tells the container to grow with its container. With pack, it's quite easy: just do myWindow.pack(fill=BOTH, expand=1). With grid, it's a bit more complicated, since you will have to configure the grid on the container.

But basically, my advice would be:
- Never make your windows inherit from Frame; make them inherit from Tk for the main window or from Toplevel for all other ones
- When you have resize problems, always check the whole widget hierarchy from the actual window down to the widget showing the problem. The cause is very often not on the widget itself, but on one of its containers.

HTH
-- 
python -c "print ''.join([chr(154 - ord(c)) for c in 'U(17zX(%,5.zmz5(17;8(%,5.Z65\'*9--56l7+-'])"



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