clearing text on canvas

[Peter Otten]

devnew at gmail.com wrote:

> i am doing  validation of contents of a folder  and need to show the
> ok/error messages on a canvas
> 
> resultdisplay =Canvas(...)
> errmessage="error!"
> okmessage="dir validation ok!"
> 
> if dirvalidate is False:

if ... is False: ...

is bad style. Just

if dirvalidate: ...

reads better and is less likely to cause subtle errors.

> resultdisplay.create_text(1,50,anchor=W,text=errmessage,width=175)
> 
> else:
> self.resultdisplay.create_text(1,50,anchor=W,text=okmessage,width=175)
> 
> 
> my problem is that if validation succeeds or fails the text created on
> canvas is displayed over the previous created text
> I need to clear the previous text from the canvas before creating new
> text
> can someone help?

You create the text once but keep its handle for further changes.

handle = canvas.create_text(...)

You can change it later with

canvas.itemconfigure(handle, ...)

Here's a short self-contained example:

import Tkinter as tk

root = tk.Tk()
canvas = tk.Canvas(root, width=100, height=100)
canvas.pack()

text_id = canvas.create_text(50, 50, width=100)

ok = False
def change_text():
    global ok
    ok = not ok
    if ok:
        text = "ok"
    else:
        text = "error"
        
    canvas.itemconfigure(text_id, text=text)

button = tk.Button(root, text="change text", command=change_text)
button.pack()

root.mainloop()

Peter