How to create a bidirectionnal binding

Merinas

Hi,

I've got two Qml element, each of them has a "test" property and this property must have always the same value. I can use a binding to link one property to another but this is not bidirectional.

Here an example of what I need.

@import QtQuick 1.0

Rectangle{
id:root

MyItem{id:a}
MyItem{id:b}

}@

Here I want a.test and b.test to to have always the same value.

grego

Why don't you just have a property alias in a and b that refers to some root element property?

Merinas

Because this will imply to know the root from my Item. And those items are suppose to be part of separate module (each of them ) so I can't force a use case like this.

sierdzio

Maybe use singal/ slots connections to connect "onChanged" of both objects? You may have to add some clever code to prevent looping, but it's not hard.

Although I would personally opt for what grego said: a global property, managed by root. As far as I see, it is perfectly doable, even when those objects are separated (some signal/ slot magic might come handy in that case).

Or use some more fancy stuff, like a shared C++ object, that all MyItems would be connected with. Or database, or a config file... right, I've got to stop right here, as I feel I am getting too abstract ;) I seems that you have to have some control from parent/ root regardless of what option you choose.

Merinas

thank to you two for your suggestion.

In fact I've got a solution, I use two binding element, because in my case those properties cannot change in the same time. So I play with the when property. But this doesn't seems right to my, it's look like makeshift job.

My two modules aren't especially written for my project so I don't want to contaminate them.

sierdzio

Might be good to make this into a feature request on JIRA, then - or even to write your own solution and submit it to Qt-project.