Placing child window relative to parent in Tkinter python

Question

I have a parent widget which contains a button. When the button is pressed I would like to open a borderless (i.e. no Windows decoration buttons) window directly underneath the parent widget aligned to the left hand side of it. I'm puzzled that the only way (it seems) of setting the position of a window is using .geometry() but worse, I can't seem to get the absolute coordinates of the parent widget - which I need for .geometry(), only the offsets from the parent's parent. So far my code is:

# This is the child which appears when the button is pressed.
class ChildPopUpWindow(Frame):
    def __init__(self, parentWgdt):
        win = Toplevel(parentWgdt)
        geom = str(parentWgdt.winfo_x()) + '+' + str(parentWgdt.winfo_y() + parentWgdt.winfo_height())
        win.overrideredirect(1) # No win decoration.
        win.bd = 10
        win.relief = GROOVE
        win.geometry( geom )
        Frame.__init__(self, win)
        # etc. etc.

     # ... and this is the handler for the button being pressed.
     def onDropDown(self):
        popUp = ChildPopUpWindow(self)

This does pop up a window but relative to the desktop, not to the parent widget. It also seems to take no account of the border thickness and relief as far as I can see. Can anyone offer a way that this can be done? Is .geometry() the way to go or are there better ways?

Answer 1

The short answer is, use winfo_rootx and winfo_rooty to get the coordinates relative to the screen. And yes, wm_geometry is the way to place a toplevel window precisely.

For example:

    x = parentWgdt.winfo_rootx()
    y = parentWgdt.winfo_rooty()
    height = parentWgdt.winfo_height()
    geom = "+%d+%d" % (x,y+height)

As a bit of friendly advice, I recommend against abbrev var nms. It makes the code hard to read, especially when the abbreviation is wrong (Wgdt should at least be Wdgt). The difference in code size between geom and geometry, and Wgdt and Widget are tiny, but the difference in readability is huge.

Answer 2

According to Tk manual "https://www.tcl.tk/man/tcl8.4/TkCmd/winfo.htm#M52" If you need the true width immediately after creating a widget, invoke update to force the geometry manager to arrange it, or use winfo reqwidth to get the window's requested width instead of its actual width.

# This code works perfectly
self.update()

self.geometry("+%d+%d" % (self.parent.winfo_rootx()+50,
                          self.parent.winfo_rooty()+50
                         )
             )