[Tutor] Tkinter, how to retrieve information about an object on canvas

[Matheus Soares da Silva]

2012/11/15 Peter Otten <__peter__ at web.de>

> Matheus Soares da Silva wrote:
>
> > Hello, I would like to be able to get information from a Tkinter canvas
> > object. (color, width, tags, root points, etc),
> >
> >  I wrote the following function that, with a canvas bind, returns me the
> > widget that has been clicked on, the widget is returned as a tuple by the
> > find_overlapping method.
> >
> > # detecting click
> > def Hasclicked(e):
> >     global obj
> >     global lastClick
> >     lastClick = [e.x, e.y]
> >     obj = e.widget.find_overlapping(e.x, e.y, e.x, e.y)
> >
> >   So, there's any method I can use on 'obj' to get the attributes?
>
> obj is a tuple of ids. You can use canvas.itemcget(id, attribute) to
> explore
> the properties of the underlying objects
>
> To get (for example) their fill-color:
>
> for id in e.widget.find_overlapping(e.x, e.y, e.x, e.y):
>     print canvas.itemcget(id, "fill")
>
> A complete example:
>
> from __future__ import division
> import Tkinter as tk
> from math import cos, sin, pi
>
> WIDTH = 640
> HEIGHT = 480
>
> root = tk.Tk()
> canvas = tk.Canvas(root, width=WIDTH, height=HEIGHT)
> canvas.pack()
>
> var = tk.StringVar()
> label = tk.Label(root, textvariable=var)
> label.pack()
>
> def canvas_click(event):
>     x, y = event.x, event.y
>     ids = canvas.find_overlapping(x, y, x, y)
>     clicked_colors = ", ".join(canvas.itemcget(id, "fill") for id in ids)
>     var.set(clicked_colors)
>
> RADIUS = 100
> R = 80
> CX = WIDTH // 2
> CY = HEIGHT // 2
>
> phi = pi/2 # 90 degree
> for color in "red", "green", "blue":
>     x = int(CX + R*cos(phi))
>     y = int(CY - R*sin(phi))
>     phi += pi*2/3 # 120 degree
>
>     canvas.create_oval(x-RADIUS, y-RADIUS, x+RADIUS, y+RADIUS, fill=color)
>
> canvas.bind("<Button-1>", canvas_click)
> root.mainloop()
>
>
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     Thank you, just what I needed.
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