How do you access properties of a QML component in C++?
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wrote on 9 Jun 2011, 18:50 last edited by
Okay so I understand you can connect signals and slots between QML and C++ objects and how to pass stuff generated in C++ to QML but how would I go about calling property of QML object for use in C++. Basically what I am trying to do is take text input from the TextInput component in QML and use it to set the currentPath() of an object which in the QDir class. I am sure I messed up a lot syntax and stuff there but I am pretty new to this.
I was thinking of doing something like
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QObject *object = view.rootObject();
QObject textIn = object->findChild<QObject>("textIn");
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and then calling text property like so and using QString to make a string.
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QString textholdervariable(textIn.text());
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and then doing the following to set my QDir path
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QDir dir;
QDir::setCurret(textholderviable);
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But this doesn't work as I get following errorrequest for member ‘text’ in ‘textIn’, which is of non-class type ‘QObject*’
Anyone know the proper way to go about retrieving properties of QML objects for use in C++?
I would also be okay with being able to set the a variable in QML equal to some variable and then being able to call that in C++.
I would also be okay with being told I am asking a stupid question and what I am talking about is impossible or there is a better way to do such a thing any help would be great.Edit: use @ tags to markup code sections please; Andre
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wrote on 9 Jun 2011, 20:13 last edited by
Look at:
"Locating child objects in QML":http://doc.qt.nokia.com/4.7-snapshot/qtbinding.html#locating-child-objects -
wrote on 9 Jun 2011, 20:16 last edited by
I have seen that but isn't that for changing the properties in QML? I am trying to take properties from the QML object and use them as inputs for C++ functions.
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wrote on 9 Jun 2011, 22:02 last edited by
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wrote on 13 Jun 2011, 14:22 last edited by
The last post helped quite a bit I am having trouble using it though can't seem to find any examples of people actually using it so not sure how I am supposed to implement that piece of code. In the form it is presented it isn't working for me. Do I need to use Q_PROPERTY macros or anything to make it work? Not really sure if what I need to make it work.
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wrote on 13 Jun 2011, 14:25 last edited by
Yes you need Q_PROPERTY in order for the moc (Meta Object Compiler) to add it to the generated MetaObject, so you can access it via these methods. If you have any further problems, just ask.
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wrote on 14 Jun 2011, 05:13 last edited by
@QObject *object = view.rootObject();
QObject textIn = object->findChild<QObject>(“textIn”);
textIn->setProperty("text","sampleText"); @See if this works.
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wrote on 14 Jun 2011, 08:20 last edited by
i have a similar problem. i managed to set a value from c++ in my qml file. the value is the x position of a qml rectangle, but when i change the value in c++ the rectangle isnt moved. What am i doing wrong?
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wrote on 14 Jun 2011, 11:13 last edited by
[quote author="Nazgul" date="1308039647"]i have a similar problem. i managed to set a value from c++ in my qml file. the value is the x position of a qml rectangle, but when i change the value in c++ the rectangle isnt moved. What am i doing wrong?[/quote]
How should we know, if you are not showing us what you are actually doing?
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wrote on 14 Jun 2011, 11:59 last edited by
I'll check to see if that works but here is something that does work really well
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QDeclarativeProperty property([name of element], "[name of property]");
@and then to call the property just do
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property.read()
property.write()
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and you can even do stuff like property.read().toString etc. this is what I was really looking for I think but thanks for all the help wouldn't have been able to find it without the leads.You still need stuff like
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QObject object = object->findChild<QObject>("rect");
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to use this thoughEdit: use @ tags to markup code sections please.
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wrote on 14 Jun 2011, 14:44 last edited by
c++ code
@QDeclarativeEngine engine;
QDeclarativeComponent component(&engine, url);
QObject *object = component.create();
if (object) {
object->setProperty("currentValue", newVal);
delete object;
object = NULL;
}@and my qml file:
@Item {
id: line
objectName: "line"
property real currentValue: 100
property real minimum: 0
property real maximum: 200
property int xMax: line.width - rect.width - 4
onCurrentValueChanged: { rect.x = 2 + (currentValue - minimum) * line.xMax / (maximum - minimum) }
signal valueChanged(real val)
width: 400
height: 20
Rectangle {
id: rect
x: 0; y: 0
width: 100; height: 20
color: "red"
MouseArea {
anchors.fill: parent
drag.axis: Drag.XAxis
drag.target: rect
drag.minimumX: 0
drag.maximumX: line.width - rect.width
onPositionChanged: {
line.currentValue = (maximum - minimum) * (rect.x-2) / line.xMax + minimum
line.valueChanged(line.currentValue)
}
}
}
}
@thanks in advance
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wrote on 14 Jun 2011, 14:49 last edited by
What is the delete statement doing on line 6 of your code? What do you expect to happen if you first set a property, and then immediately delete the object?
What you are doing here, is creating an object, setting a property on it, and then immediately disposing of it again. That seems like a rather useless thing to do. Instead, you should try to find the object you wish to manipulate, and then modify its properties. Or, perhaps better from a QML/declarative way of thinking kind-of-perspective, you should create a QObject derived object, give it properties for the position, insert it into your QML environment, and bind to these properties.
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wrote on 14 Jun 2011, 14:57 last edited by
@QObject* obj = mDeclarativeView->rootObject();
if (obj) {
obj->setProperty("currentValue", newVal);
}@ok, i wasnt sure about a memory leak because the method was create.
i changed my code to the above and made sure obj != null. obj is a qml object with name = "line"
thats fine so far but still the setProperty has no effect. -
wrote on 15 Jun 2011, 12:16 last edited by
no ideas about my problem?
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