From AutoIt Wiki

Function Reference

Retrieves the internal handle of a window.

WinGetHandle ( "title" [, "text"] )

Parameters

title	The title of the window to read. See Title special definition.
text	[optional] The text of the window to read.

Return Value

Success:	Returns handle to the window.
Failure:	Returns "" (blank string) and sets @error to 1 if no window matches the criteria.

Remarks

This function allows you to use handles to specify windows rather than "title" and "text".
Once you have obtained the handle you can access the required window even if its title changes.

Related

WinSetTitle, GUICreate, WinList

Example

; Identify the Notepad window that contains the text "this one" and get a handle to it

Change into the WinTitleMatchMode that supports classnames and handles

AutoItSetOption("WinTitleMatchMode", 4)

Get the handle of a notepad window that contains "this one"

$handle = WinGetHandle("classname=Notepad","this one")
If @error Then
MsgBox(4096,"Error","Could not find the correct window")
Else

Send some text directly to this window's edit control

ControlSend($handle,"","Edit1","AbCdE")
EndIf