Hello ,

I am facing some confusion regarding passing data between the qt qick slider and QQuickItem object in C++, that results in application crash. I have the following class with the defined properties:

Qt Code: 
  1. class TessellationSceneItem : public QQuickItem
  2. {
  3.     Q_OBJECT
  4.     //the property defintion must be at the top of the class
  5.     //the notify signal is needed for correct property bindings
  6.     Q_PROPERTY(float outer READ outer WRITE setOuter NOTIFY outerChanged)
  7.     Q_PROPERTY(float inner READ inner WRITE setInner NOTIFY innerChanged)
  8.     Q_PROPERTY(float maxPatchVertices READ maxPatchVertices NOTIFY maxPatchVerticesChanged)
  9.  
  10. public:
  11.     TessellationSceneItem();
  12.  
  13.     void setOuter(float);
  14.     void setInner(float);
  15.  
  16.     float inner();
  17.     float outer();
  18.  
  19.     float maxPatchVertices() const;
  20.  
  21. signals:
  22.     void innerChanged();
  23.     void outerChanged();
  24.     void maxPatchVerticesChanged();
  25. .............
  26. ............
  27. private:
  28.  
  29.     TeapotTessellation* mTessScene;
  30.  
  31.     QTime mTIme;
  32.  
  33. };
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The definition of the setter and getter methods:

Qt Code: 
  1. void TessellationSceneItem::setOuter(float outerFactor)
  2. {
  3.     if(outerFactor == mTessScene->outerTessellationFactor())
  4.         return;
  5.  
  6.     mTessScene->setOuterTessellationFactor(outerFactor);
  7.     //do not emit notifier if value does not actually change
  8.     emit outerChanged();
  9. }
  10.  
  11. void TessellationSceneItem::setInner(float innerFactor)
  12. {
  13.     if(innerFactor == mTessScene->innerTessellationFactor())
  14.         return;
  15.  
  16.     mTessScene->setInnerTessellationFactor(innerFactor);
  17.     emit innerChanged();
  18. }
  19.  
  20. float TessellationSceneItem::inner()
  21. {
  22.     return (float)(mTessScene->innerTessellationFactor());
  23. }
  24.  
  25. float TessellationSceneItem::outer()
  26. {
  27.     return (float)(mTessScene->outerTessellationFactor());
  28. }
  29.  
  30. float TessellationSceneItem::maxPatchVertices() const
  31. {
  32.     return (float) (mTessScene->getMaxPatchVertices());
  33. }
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The idea is to have the slider value loaded with the value set in the underlying C++ application. Then with every slider interaction , the underlying value( outer, inner) in the C++ side will be updated. I tried the following in the .qml file , but the application crashes.

Qt Code: 
  1. import QtQuick 2.0
  2. import QtQuick.Controls 1.1
  3. import QtQuick.Layouts 1.1
  4. import TeapotTessellation 1.0
  5.  
  6. Item {
  7.     id: root
  8.     width: 512; height: 512
  9.  
  10.  
  11.     TessellationSceneItem
  12.     {
  13.         id: tessSceneItem
  14. //        outer: outerTessellationSlider.value
  15. //        inner: innerTessellationSlider.value
  16.     }
  17.  
  18.     GridLayout {
  19.         id: controlLayout
  20.         columns: 2
  21.  
  22.         Text {
  23.              id: outerTessellationText
  24.              text: qsTr("Outer Tess. Factor: ")
  25.              color: "black"
  26.              opacity: 1.0
  27.          }
  28.  
  29.          Slider {
  30.              id: outerTessellationSlider
  31.              opacity: 1.0
  32. //             value: tessSceneItem.outer
  33.              minimumValue: 1.0
  34.              maximumValue: 64//tessSceneItem.maxPatchVertices
  35.              stepSize: 1.0
  36.              Layout.fillWidth: true
  37.          }
  38.  
  39.  
  40.          Text {
  41.              id: innerTessellationText
  42.              text: qsTr("Inner Tess. Factor: ")
  43.              color: "black"
  44.              opacity: 1.0
  45.          }
  46.  
  47.  
  48.  
  49.          Slider {
  50.              id: innerTessellationSlider
  51.              opacity: 1.0
  52. //             value: tessSceneItem.inner
  53.              minimumValue: 1.0
  54.              maximumValue: 64.0//tessSceneItem.maxPatchVertices
  55.              stepSize: 1.0
  56.              Layout.fillWidth: true
  57.          }
  58.     }
  59.  
  60.  
  61.     Rectangle {
  62.         id: rect
  63.         color: "red"
  64.         radius: 10
  65.         opacity: 0.1
  66.         border.color: "black"
  67.         anchors.fill: controlLayout
  68.     }
  69. }
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The commented part of the .qml file are the places that cause the application crash. Any hint ?

Thanks