Using a Loader for a string of QML

Question

In Qt 5.3 I've been using the Loader QML element for loading screens, loading the view from a QML file in the background. Now I'm trying to load a string of QML dynamically. Qt.createQmlObject enables me to do so, but I can't seem to get the Loader element to play along.

Seems like Loader only takes a URL (QUrl) or component (QQmlComponent), but Qt.createQmlObject creates an object (QObject).

I'm new to QML, but from my understanding components are reusable elements, similar to classes, and objects are the instances of those classes. I thus can't seem to wrap my head around why Loader wouldn't work with objects.

How can I show a loading screen while (asynchronously) parsing and initializing a string of QML?

Example QML code:

Item {
    Rectangle {id: content}

    Loader {id: loader}

    Component.onCompleted: {
        var obj = Qt.createQmlObject('import QtQuick 2.3; Rectangle {}', content);

        loader.source = obj; // Throws error.
    }
}

Mitch · Accepted Answer · 2014-06-08 08:47:37Z

1

It's not possible using the current API. As Loader's documentation says, it loads objects via a URL that points to a QML file or a Component:

import QtQuick 2.0

Item {
    Rectangle {
        id: content
        anchors.fill: parent
        color: "grey"

        Loader {
            id: loader
            sourceComponent: myComponent
            anchors.fill: parent
            anchors.margins: 40
        }
    }

    property Component myComponent: Qt.createComponent("MyComponent.qml", Component.Asynchronous)
}

MyComponent.qml:

import QtQuick 2.2

Rectangle {
   color: "red"
}

edited Jun 8, 2014 at 8:47

answered Jun 7, 2014 at 20:55

Mitch

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5 Comments

Robbert Over a year ago

Hi Mitch, thanks for chiming in. Though this is a good example of a Loader loading a QML file, I'm actually looking for a way to apply a Loader to a QML string. In other words: is there some way to do Qt.createComponent(QString string) rather than Qt.createComponent(QUrl url)?

Mitch Over a year ago

No, that's what my answer was trying to say. I've updated it.

Robbert Over a year ago

Still, there should be some way to load strings of QML asynchronously. Perhaps I need to write a Loader subclass. Either way, thanks for your input Mitch.

Mitch Over a year ago

No worries. You may want to create a suggestion on bugreports.qt-project.org for this, as well.

Robbert Over a year ago

Good call. I just created one: bugreports.qt-project.org/browse/QTBUG-39529

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