Problem displaying images with TkInter

[David]

Ok, that's working now. Thanks for the tip!

David

Eric Brunel wrote:

> David wrote:
>> Hi,
>>         I'm new to python so I'm probably making a fairly simple mistake,
>>         but
>> look at the example below. It simply displays a rectangle and an image.
>> 
>> -------------------------------------------------
>> from Tkinter import *
>> 
>> root = Tk()
>> 
>> c = Canvas(root, width=1024, height = 1024)
>> c.pack()
>> 
>> c.create_rectangle(10,10,50,50)
>> mudPhoto = PhotoImage(file="/root/metropolis/mud.gif")
>> c.create_image(50, 50, anchor=NW, image=mudPhoto)
>> 
>> root.mainloop()
>> -----------------------------------------------
>> 
>> Now I try to modify it so that the image and rectangle only appear when I
>> click the mouse on the canvas. I use the following code:
>> 
>> -----------------------------------------------
>> from Tkinter import *
>> 
>> root = Tk()
>> 
>> def OnClick(event):
>>     print "click!!!"
>>     c.create_rectangle(10,10,50,50)
>>     mudPhoto = PhotoImage(file="/root/metropolis/mud.gif")
>>     c.create_image(50, 50, anchor=NW, image=mudPhoto)
>> 
>> c = Canvas(root, width=1024, height = 1024)
>> c.pack()
>> c.bind("<Button-1>",OnClick)
>> root.mainloop()
>> ----------------------------------------------
>> 
>> However when I click the mouse it prints 'click!!!' and draws the
>> rectangle as expected. However it doesn't draw the image! Does anyone
>> have any idea why this would be?
> 
> This used to be a FAQ, but I can't it anymore (anyone knows where it has
> gone?).
> 
> The problem lies in the fact that for some reason, the Canvas where you do
> the create_image does *not* keep a reference on the actual PhotoImage
> object. So this object disappears when your variable mudPhoto goes out of
> scope (i.e. at the end of your OnClick function), which causes its
> deletion at tk level. So when OnClick finishes, the canvas finds itself
> displaying an image that doesn't exist anymore.
> 
> The workaround is simple: always keep an explicit reference on all your
> PhotoImage and BitmapImage objects until you no more need them. For your
> particular case, this can be done via:
> 
> def OnClick(event):
>      print "click!!!"
>      c.create_rectangle(10,10,50,50)
>      c.mudPhoto = PhotoImage(file="/root/metropolis/mud.gif")
>      c.create_image(50, 50, anchor=NW, image=c.mudPhoto)
> 
> Turning mudPhoto into an attribute of the canvas ensures that it won't be
> deleted before the canvas is.
> 
> HTH