How to connect a JavaScript function to a property signal?

Question

I'm new to Qml and having some trouble connecting a javascript handler to a property's signal. I have a C++ object with a property and signal.

class CppObject : public QObject
{
    Q_OBJECT
    Q_PROPERTY(QVariant value READ getValue WRITE setValue NOTIFY valueChanged)

signals:
    void valueChanged(const QVariant &);
};

The objects are created through a C++ factory method and I'm able to bind the values and changes to Qml properties. This all works.

property CppObject obj: cppProxy.PropertyFactory("foo");

Text
{
    x: 100;
    y: 100;
    text: parent.obj.value;
}

For some properties, I'd like to connect the valueChanged signal to a javascript function. I've been up and down through the Qml documentation and have tried a bunch of stuff without any luck. I figured something like this should work, but doesn't

function objEventHandler()
{
    console.log('objEventHandler() ran')
}

Component.onCompleted:
{
    obj.value.valueChanged.connect(objEventHandler);
}

What is the best way to do this?

MartinJ · Accepted Answer · 2013-02-15 22:21:25Z

5

You can also connect as you've tried in your example, but the form is:

Component.onCompleted:
{
    obj.valueChanged.connect(objEventHandler);
}

The signal is not a property of the 'value' object, but of 'obj'.

answered Feb 15, 2013 at 22:21

MartinJ

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1 Comment

Chris Dolan Over a year ago

One additional complication I came across is that "this" is not always well defined in signal handlers if you're getting a signal from C++. So, in this example I had to use a closure to retain access to the "obj" context, like this: Component.onCompleted: { var o = obj; obj.valueChanged.connect(function() { console.log(o.text); }); }

uroc · Accepted Answer · 2013-02-15 18:46:45Z

2

It's simple using the connections object.

Connections
{
    target: obj;
    onValueChanged: console.log('changed');
}

answered Feb 15, 2013 at 18:46

uroc

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