Problem using Binding QML element

Alicemirror

Hi to all,

I am trying to see how the Binding element works but I see in the documentation only examples related to a single bind association. In the documentation I see always examlpes related to QML objects properties and C++ properties exposed to QML. I suppose that it is only one of the possible cases... In a situation like the following example
@
Binding {
target: background
property: "color"
value: Methods.getColor("background"); // a js functions
when: dataParameters.dataReady
// dataParameres.dataReady is a flag initially set to false
// that a signal changes to true.
}

// The background default color
Rectangle {
    id: background
    width: parent.width; height: parent.height
}

@
if I need to set the binding of my object not only for the color property but also width and height should I create three different Binding instances or I can manage all of them together and how I can do?

Thank you for any suggestion.

vsorokin

I just open Qt sources for check your question and it seems like one Binding element - one property:

@class QDeclarativeBindPrivate : public QObjectPrivate
{
public:
QDeclarativeBindPrivate() : when(true), componentComplete(true), obj(0) {}

bool when : 1;
bool componentComplete : 1;
QObject *obj;
QString prop;
QDeclarativeNullableValue<QVariant> value;

};
@

Alicemirror

Thank you. This means that is unuseful. In the meanwhile I have analized the general question. The problem is that until a specific element (the configuration parameters) is not loaded any of the parametrized elements can be assigned with the function because it returns an error condition.
In the case of QML-to-QML the solution is to manage the assignements instead bindings with signals. I saw it more efficient and reliable.

vsorokin

May be states can help you.
Something like:
@
// The background default color
Rectangle {
id: background
width: parent.width; height: parent.height

    states: [ State {
         when: dataParameters.dataReady
         PropertyChanges {
              target: background
              color: Methods.getColor("background"); // a js functions
         }
         PropertyChanges {
              target: foreground
              color: Methods.getColor("foreground"); // a js functions
         }
    }
    ]
}@

Alicemirror

Thank you Vass :)

At the moment I have adopted this solution:
@
// Header banner
Framework.Loader {
id: appTopBanner;
width: parent.width;
signal configReady

    onConfigReady: {
        fontPoints: Methods.jsonConfig.
        obj_color = Methods.jsonConfig.colors[0].headerMenu;
        height = Methods.jsonConfig.pixels[0].headerHeight;
        obj = "TextHeader"
    }
}

@
This works and I think it is almost analog to yours. The difference is that I can fire a signal to the whole page and all the childs and subchilds etc. in the inherit tree can catch the same signal.

You method instead has the advantage that I can join more different targets in the same place.

What is the best method? What is your opinion ? I am attracted byt both...

vsorokin

[quote author="Alicemirror" date="1316331482"]What is the best method? What is your opinion ?[/quote]

I think it depends on your goals and your preferences.

Alicemirror

My thought is that probably the signals are more flexible but a bit more complex because need a signal definition in every object.

Your method has the advantage that can be managed externally.

Remain - I think in both cases - the problem that the second level child objects can't be updated directly. Or I am wrong ?