ListItem: setting implicitHeight has no effect

[Andrea Bernabei]

ubuntu-ui-toolkit/staging, r2133

Description:
Creating a ListItem and setting its implicitHeight has no effect.
This means any component that derives from ListItem has to be implemented setting its height, while the best practice (as far as I know) is that components are supposed to set their implicit size, and leave the "real" size to the user of those components.

Investigation:
I spent some time on investigating this already. The problem is:
- http://bazaar.launchpad.net/~ubuntu-sdk-team/ubuntu-ui-toolkit/staging/view/2133/src/UbuntuToolkit/uclistitem.cpp#L1128
This means every time the width of the parent changes, ListItem will reset its implicit height to the default value. As a consequence, specifying a custom implicit height value is not allowed, because any parent's width change would cause it to be overwritten.
- http://bazaar.launchpad.net/~ubuntu-sdk-team/ubuntu-ui-toolkit/staging/view/2133/src/UbuntuToolkit/uclistitem.cpp#L1130 At this point the item has the implicitHeight set by the testcase below. Calling _q_updateSize overwrites what the user set.

Testcase:
import QtQuick 2.4
import Ubuntu.Components 1.3

Item {
    width: units.gu(42)
    height: units.gu(75)
    ListItem {
        id: menu
        Component.onCompleted: console.log(height, implicitHeight)

        //This is overridden on ListItem init and on every parent's width change.
        //It is as if it weren't there
        implicitHeight: 5000

        //Explicitly setting height is the only way to resize the component
        height: 5000

        Rectangle {
            anchors.fill: parent
            color: "blue"
        }
    }
}

[Marco Trevisan (Treviño) (3v1n0)]

I've noticed all this by using ListItemLayout's as ListItem main child, with variable height...
When resizing the main window, the items were collapsing

See attached videos.