I would say #7:

Try to reduce the amount of magic to an absolute minimum. If you have MenuItems 
seemingly in a Menu but really they end up in a container then you run into 
troubles like this. IMHO it's better to make the user type a little bit more 
but have it be very clear what happens. I don't know of any project that was 
late because developers couldn't type fast enough. :)

So my personal recommendation would be to not have a magical column but rather 
an explicit MenuLayout. Make the QML hierarchy reflect what really happens 
instead of trying to save the user from typing a few more characters. Less 
magic means developers understand the code better. It's  a tradeoff worth 
making.

Peppe

From: "ext [email protected]<mailto:[email protected]>" 
<[email protected]<mailto:[email protected]>>
Date: Thu, 17 Mar 2011 07:38:43 +0000
To: <[email protected]<mailto:[email protected]>>
Subject: [Qt-qml] internal re-parenting of child items


Hi,
Is there any recommended patters how to handle internal re-parenting of child 
items?

I’ll open up the scenario with a small example. Let’s take imaginary QML 
components as Menu and MenuItem (both derived from QML Item). The idea would be 
that the application developer would be able to write:

Menu {
    id: optionsMenu
    MenuItem {…}
    MenuItem {…}
    MenuItem {…}
}

To populate the menu. Internally the Menu would like to use QML Column element 
as middle-man to layout the items as:

*Menu.qml*
Item {
    default property alias content: layout.children
    Column { id: layout; anchors.fill: parent }
}

This works like magic until someone wants to dynamically add another MenuItem:
var newMenuItem = new MenuItem(optionsMenu) // wrong parent!
or
menuItemComponent.creatObject(optionsMenu) // wrong parent!

This fails miserably and the only way this could be achieved is that the user 
of the Menu component would know the internal structure and would be able to 
write something nasty.

What would be the recommended pattern?
#1 never change the default property
#2 never mix’n’match static and dynamic allocation of child items
#3 expose middle-man as ‘container’ property which can be used in dynamic 
allocation
#4 provide always functions to add/remove dynamic stuff
#5 re-parent dynamically added children to the middle-man inside the 
onChildrenChanged
#6 let the user do the nasty bit – they can make it work if they really want to
#7 something else?

Thanks,
Pekka




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