How to get tkinter canvas to dynamically resize to window width?

I need to get a canvas in tkinter to set its width to the width of the window, and then dynamically re-size the canvas when the user makes the window smaller/bigger.

Is there any way of doing this (easily)?

Solution 1:

I thought I would add in some extra code to expand on @fredtantini's answer, as it doesn't deal with how to update the shape of widgets drawn on the Canvas.

To do this you need to use the scale method and tag all of the widgets. A complete example is below.

from Tkinter import *

# a subclass of Canvas for dealing with resizing of windows
class ResizingCanvas(Canvas):
    def __init__(self,parent,**kwargs):
        Canvas.__init__(self,parent,**kwargs)
        self.bind("<Configure>", self.on_resize)
        self.height = self.winfo_reqheight()
        self.width = self.winfo_reqwidth()

    def on_resize(self,event):
        # determine the ratio of old width/height to new width/height
        wscale = float(event.width)/self.width
        hscale = float(event.height)/self.height
        self.width = event.width
        self.height = event.height
        # resize the canvas 
        self.config(width=self.width, height=self.height)
        # rescale all the objects tagged with the "all" tag
        self.scale("all",0,0,wscale,hscale)

def main():
    root = Tk()
    myframe = Frame(root)
    myframe.pack(fill=BOTH, expand=YES)
    mycanvas = ResizingCanvas(myframe,width=850, height=400, bg="red", highlightthickness=0)
    mycanvas.pack(fill=BOTH, expand=YES)

    # add some widgets to the canvas
    mycanvas.create_line(0, 0, 200, 100)
    mycanvas.create_line(0, 100, 200, 0, fill="red", dash=(4, 4))
    mycanvas.create_rectangle(50, 25, 150, 75, fill="blue")

    # tag all of the drawn widgets
    mycanvas.addtag_all("all")
    root.mainloop()

if __name__ == "__main__":
    main()

Solution 2:

You can use the .pack geometry manager:

self.c=Canvas(…)
self.c.pack(fill="both", expand=True)

should do the trick. If your canvas is inside a frame, do the same for the frame:

self.r = root
self.f = Frame(self.r)
self.f.pack(fill="both", expand=True)
self.c = Canvas(…)
self.c.pack(fill="both", expand=True)

See effbot for more info.

Edit: if you don't want a "full sized" canvas, you can bind your canvas to a function:

self.c.bind('<Configure>', self.resize)

def resize(self, event):
    w,h = event.width-100, event.height-100
    self.c.config(width=w, height=h)

See effbot again for events and bindings

Solution 3:

This does it - in my version of Python at least. The canvas resizes both horizontally (sticky=E+W & rowconfigure) and vertically (sticky=N+S & columnconfigure). I've set the canvas background to a disgusting colour - but at least you can see when it works.

from tkinter import *
root=Tk()
root.rowconfigure(0,weight=1)
root.columnconfigure(0,weight=1)
canv=Canvas(root, width=600, height=400, bg='#f0f0c0')
canv.grid(row=0, column=0, sticky=N+S+E+W)
root.mainloop()