How to Connect C Signals to QML Slots with Primitive Types?

Connecting C Signal to QML Slot with Primitive Types

In Qt, signals and slots enable seamless communication between C and QML components. This interaction is crucial for building complex and responsive UIs. However, transmitting data types other than primitives can introduce errors.

Consider the scenario where you want to send a QString from a C signal to a QML slot. By default, this connection fails with an error similar to:

Object::connect: No such slot QDeclarativeRectangle_QML_2::updateViewWithItem(QString)

Solution: Using Qt Connections

To resolve this issue, you must use Qt Connections to connect slots to signals. Connections allow for more flexibility and support the passing of non-primitive data types.

Steps:

1. Exposing C Object in QML:
   Expose your C object myObj in the QML file using setContextProperty.

   <code class="c++">qmlVectorForm->rootContext()->setContextProperty("YourObject", myObj);</code>

2. Signal Definition:
   Define the signal in C :

   <code class="c++">finishedGatheringDataForItem(QString signalString)</code>

3. QML Connection:
   In the QML file, add connections as follows:

   <code class="qml">Connections {
       target: YourObject
       onFinishedGatheringDataForItem: {
           qmlString = signalString
       }
   }</code>

By using Qt Connections, you can now pass QString values from your C signal to your QML slot effectively.

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