ChildrenRect always returns 0

Question

I have a Flickable item in where I want to put a customized flow component, so I created the Flickable like this:

import QtQuick 2.0
import UICore.Layouts 1.0 as Layouts
Flickable{
    anchors.fill: parent;
    contentWidth: parent.width;
    contentHeight: flow.childrenRect.height;

    Component.onCompleted: {
        console.log("The content height is: " + contentHeight);
    }


}

Then in my main.qml I have this (The file above is MyFlickable, and the MyFlow is a flow with specific properties):

 MyFlickable{
        ....
        MyFlow{
            id: flow
         ... 
        }
  }

This works great but the problem is that I want to be able to reuse this item with as little overhead as possible. Setting the id inside of my MyFlow doesn't work, and I tried this

contentHeight: contentItem.childrenRect.height

as suggested in here under contentWidth section: http://doc.qt.io/qt-5/qml-qtquick-flickable.html#contentItem-prop

but that always returns 0. I've tried a couple of other ways to receive onCompleted signals but I get the same luck. This doesn't work for example:

contentHeight: children[0].childrenRect.height

Which in my mind should be the same as accessing the item through the id, bu apparently not.

So my question is: how do I get to height of my flow after all the components have been added?

Thanks in advance!

Could you pleas post a [minimal, complete and verifiable example](https://stackoverflow.com/help/mcve)? I am completly confused by this `Layout.FlickableGridLayout`-thingy. Where does this come from? Where do you try to set the `contentHeight`? — derM - not here for BOT dreams, Jul 13 '17 at 22:24
This was the file that I shared. I just edited. I hope that it's clearer now! — Felipe Centeno, Jul 13 '17 at 23:02

Mark Ch · Accepted Answer · 2017-07-14T18:11:22.663

2

This wlil achieve what you want:

contentHeight: contentItem.children[0].childrenRect.height

From Qt docs

Items declared as children of a Flickable are automatically parented to the Flickable's contentItem. This should be taken into account when operating on the children of the Flickable; it is usually the children of contentItem that are relevant.

But I must say it is bad practice for a component to make assumptions about things outside its own QML file, as it makes the component difficult to reuse. Specifically in this case the Flickable is making the assumption that its first child is of a Component type that makes use of the childrenRect property. Your MyFlow component does, but many other components do not, for example an Image.

edited Jul 14 '17 at 18:11

answered Jul 14 '17 at 06:34

Mark Ch

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Well that works, but I'm confused. What is contentItem.children[0]? is contentItem the flickable itself? and children[0] the flow? – Felipe Centeno Jul 14 '17 at 16:50
Ok thanks for the help! That explains what I was seeing. I think it's weird that they are declared as children of contentItem instead of flickable itself. – Felipe Centeno Jul 14 '17 at 18:41
2

@FelipeCenteno it's quite common. A lot of QML Items have what is called a "default property" for their children to be parented to. If children were parented to the Flickable directly then the scene graph would render them immediately and the Flickable would not be able to work it's magic. – Mark Ch Jul 14 '17 at 18:48

ChildrenRect always returns 0

1 Answers1