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Weird behavior with $WS_EX_MDICHILD


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Hello everyone,

I have noticed a weird behavior when using $WS_EX_MDICHILD.

I create a main GUI with 2 buttons.

Each button creates a new GUI.

The first one without $WS_EX_MDICHILD.

The second one with $WS_EX_MDICHILD.

I click the first one and the other GUI is created (without $WS_EX_MDICHILD):

If I drag the main GUI the other GUI is separate and doesn't move, which is expected.

Then I click the second one for the next GUI to be created (with $WS_EX_MDICHILD):

If I now drag the main GUI, both of the other GUIs move with it.

If I close the second GUI, the first one still moves if I drag the main one.

If I close the first one and re-open it, it still moves in relation to the Main GUI (if I drag the main GUI it follows)

Is this how it's supposed to be? Does the style affect all GUIs created even without the style?

Here is a script to try it out:

(Follow the instructions above)

#include <GUIConstantsEx.au3>
#include <WindowsConstants.au3>

Opt("GUIOnEventMode", 1)
Opt("GUICloseOnESC", 0)

Global $Main


Func MainGUI()
    $Main = GUICreate("Main", 350, 350)
    GUISetOnEvent($GUI_EVENT_CLOSE, "WindowClose")
    $button1 = GUICtrlCreateButton("Child 1 - no MDI_CHILD", 75, 100, 150, 20)
    GUICtrlSetOnEvent($button1, "Child1")
    $button2 = GUICtrlCreateButton("Child 2 - with MDI", 75, 150, 150, 20)
    GUICtrlSetOnEvent($button2, "Child2")
    GUISetState(@SW_SHOW, $Main)

Func Child1()
    $ChildGUI1 = GUICreate("Child 1 - no MDI_CHILD", 180, 180, 100, 100, Default, Default, $Main)
    GUISetOnEvent($GUI_EVENT_CLOSE, "WindowClose")
    GUISetState(@SW_SHOW, $ChildGUI1)

Func Child2()
    $ChildGUI2 = GUICreate("Child 2 - with MDI", 180, 180, 100, 100, Default, $WS_EX_MDICHILD, $Main)
    GUISetOnEvent($GUI_EVENT_CLOSE, "WindowClose")
    GUISetState(@SW_SHOW, $ChildGUI2)

Func WindowClose()
    If @GUI_WinHandle = $Main Then

While 1

I know the example can be coded better (e.g. one function for both GUIs and using @GUI_CTRLHANDLE but this does the job for now)

Edited by AoRaToS

s!mpL3 LAN Messenger

Current version [04/07/2019]

s!mpL3 LAN Messenger.zip


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The child GUIs are created with exactly the same style and extended style values and these do not change as the GUIs are deleted and recreated. The Help file does tell us that the $WS_EX_MDICHILD style is not true MDI - so I can only imagine that AutoIt is doing something "under the hood" to get the child to follow the main GUI and this affects all children. :wacko:

I will ask trancexx to pop in and take a look - she will doubtless be able to give you the correct explanation. :)


Public_Domain.png.2d871819fcb9957cf44f4514551a2935.png Any of my own code posted anywhere on the forum is available for use by others without any restriction of any kind

Open spoiler to see my UDFs:


ArrayMultiColSort ---- Sort arrays on multiple columns
ChooseFileFolder ---- Single and multiple selections from specified path treeview listing
Date_Time_Convert -- Easily convert date/time formats, including the language used
ExtMsgBox --------- A highly customisable replacement for MsgBox
GUIExtender -------- Extend and retract multiple sections within a GUI
GUIFrame ---------- Subdivide GUIs into many adjustable frames
GUIListViewEx ------- Insert, delete, move, drag, sort, edit and colour ListView items
GUITreeViewEx ------ Check/clear parent and child checkboxes in a TreeView
Marquee ----------- Scrolling tickertape GUIs
NoFocusLines ------- Remove the dotted focus lines from buttons, sliders, radios and checkboxes
Notify ------------- Small notifications on the edge of the display
Scrollbars ----------Automatically sized scrollbars with a single command
StringSize ---------- Automatically size controls to fit text
Toast -------------- Small GUIs which pop out of the notification area


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