Visualization of dynamic c++ list with positions as set of Items in QML-app at corresponding positions.



  • Some c++ class periodically sends a list of items with positions inside (x and y). It needs to be visualized on grids and axis I've created in QML.
    For representation of item I've prepared black rectangle in Rect.qml file.
    Is it possible to:

    • represent each item using rect.qml (like appearance of item)
    • not using paint(...) from QQuickPaintedItem and updatePaintNode(...) from QQuickItem respectively
    • place each item in some QML container (like Rectangle) with corresponding (x and y) from list ?
      I didn't find any straight way to do this.

    I know i could use QGraphicsScene and QPainter with QMainWindow GUI without any "qml" but i want to use benefits of QML interface.


  • Moderators

    @ilyaik How does the list of items look like ?
    One way to implement would be using Connections. Set the target as your C++ class which I assume you have set as a context property. Then when ever the new list is sent through as signal, grab it inside the corresponding handler in QML. Once you get the list iterate over it and then set x and y coordinates of the Black rectangles. For this you can keep a list of Black rectangles in QML array.



  • @p3c0 This is an idea!
    List is a QList<struct {int x; int y}>

    But as it always happens... after 1 day of searching solution appears only after asking a question on forum =)

    I did as you said: a C++ class myList with QList inside. I made this class as a context property. Class has Q_PROPERTY (int count READ count NOTIFY countChanged) that is the size of QList.
    In QML part i've placed

    Repeater { 
       model: myList.count;
       Rectangle {
          // black rectangle
            ...
            x: myList.xPosition(index)
            y: myList.yPosition(index)
       }
    }
    

    myList has xPosition(index) and yPosition(index) slots recpectively.

    And it works.
    Thank you for help!


  • Moderators

    @ilyaik You're Welcome :)
    Using Repeater is also a good idea. You can mark the post as solved if done.



  • I've faces a new problem.

    If QList inside myClass changed it's values, but count myList.count didn't, Repeater doesn't updates. That's ok... strictly speaking the Repeater's model myList.count didn't change.
    I made a signal from myClass updateSignal. updateSignal emits when data inside list in myClass is updated. In QML this signal is exposed in Connections part.

    Connections {
            target: myClass
            onUpdateSignal {
                repeater.model = 0
                repeater.model = myClass.count
            }
    }
    
    // And Repeater part
    
    Repeater { 
        id: repeater
        model: 0
        Rectangle {
          // black rectangle
            ...
            x: myList.xPosition(index)
            y: myList.yPosition(index)
        }
    }
    

    It renewsrepeater.
    But it seams that it's like a crutch.
    Is there any proper way to renew Repeater?

    P.S. repeater.update() didn't help.


  • Moderators

    @ilyaik That is a valid way. Bindings are meant for that.
    Also it should work even without first assigning model to 0 in Connections.



  • No. Repeater doesn't renew without assigning model to 0 in Connections. It seems like nothing changes for Repeater if myClass.count stays unchanged.


  • Moderators

    @ilyaik That means the count didnot change

    repeater.model = myClass.count
    

    the Repeater will update only when the property changes. That is how Binding works.



  • So that's why i use assigning model to 0 in Connections to force Repeater to renew itself when count stays unchanged.


  • Moderators

    @ilyaik Ok. So is it that you only want to update x and y positions even if no new item is added ?



  • Yes. If myClass's QList changes inside


  • Moderators

    @ilyaik then I think my first post could be the possible way.



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