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  4. Why does my QGraphicsSimpleTextItem not display any plot information when I move my mouse?
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Why does my QGraphicsSimpleTextItem not display any plot information when I move my mouse?

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  • E Offline
    E Offline
    engsml
    wrote on last edited by
    #1

    I have the following function that will display the x and y values of my QChart when my cursor moves:

    void constellationmockup::mouseMoveEvent(QMouseEvent *event)
    {
    m_coordX->setText(QString("X: %1").arg(chart->mapToValue(event->pos()).x()));
    m_coordY->setText(QString("Y: %1").arg(chart->mapToValue(event->pos()).y()));

    }

    where m_coordX and m_coordY are QGraphicsSimpleTextItems. I am able to set their position using this function: m_coordY->setPos("some points")

    The problem is that it will only display the points when my mouse is outside of my plot. When my mouse is hovering inside my plot area, it will not display any information. It pretty much "freezes" until I move my mouse outside of the plot.

    For reference, I got the solution from this function from the "callout" example in QtCreator:

    void View::mouseMoveEvent(QMouseEvent *event)
    {
    coordX->setText(QString("X: %1").arg(m_chart->mapToValue(event->pos()).x()));
    coordY->setText(QString("Y: %1").arg(m_chart->mapToValue(event->pos()).y()));
    QGraphicsView::mouseMoveEvent(event); //I did try inserting this into my function, but I get an error if I include this.
    }

    Any help would be much appreciated. I definitely seem to be missing something!

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    • mrjjM Offline
      mrjjM Offline
      mrjj
      Lifetime Qt Champion
      wrote on last edited by
      #2

      Hi
      you might need to enable mouse tracking
      http://doc.qt.io/qt-5/qwidget.html#mouseTracking-prop
      not sure if constellationmockup is a QWidget.
      Or you need to set on other object, but its not always
      enabled and it only send moveEvents if button is pressed.

      E 1 Reply Last reply
      1
      • mrjjM mrjj

        Hi
        you might need to enable mouse tracking
        http://doc.qt.io/qt-5/qwidget.html#mouseTracking-prop
        not sure if constellationmockup is a QWidget.
        Or you need to set on other object, but its not always
        enabled and it only send moveEvents if button is pressed.

        E Offline
        E Offline
        engsml
        wrote on last edited by
        #3

        @mrjj It is a QWidget. Does that make a difference?

        mrjjM 1 Reply Last reply
        0
        • E engsml

          @mrjj It is a QWidget. Does that make a difference?

          mrjjM Offline
          mrjjM Offline
          mrjj
          Lifetime Qt Champion
          wrote on last edited by
          #4

          @engsml
          Nope, that's perfect. Normally it wont send mouseMove to QWidgets as far as i recall
          and you need to set mouseTracking to true to have them come without mouse buttons being pressed.

          E 1 Reply Last reply
          0
          • mrjjM mrjj

            @engsml
            Nope, that's perfect. Normally it wont send mouseMove to QWidgets as far as i recall
            and you need to set mouseTracking to true to have them come without mouse buttons being pressed.

            E Offline
            E Offline
            engsml
            wrote on last edited by
            #5

            @mrjj Yeah, the mouseMoveEvent works on everything but the actual QChart. I can only get the x and y points to display when I left click and drag it into the chart area. Otherwise it won't work. Would I have to include this function: QChartView::mouseMoveEvent(event) for it to work?

            mrjjM 1 Reply Last reply
            0
            • E engsml

              @mrjj Yeah, the mouseMoveEvent works on everything but the actual QChart. I can only get the x and y points to display when I left click and drag it into the chart area. Otherwise it won't work. Would I have to include this function: QChartView::mouseMoveEvent(event) for it to work?

              mrjjM Offline
              mrjjM Offline
              mrjj
              Lifetime Qt Champion
              wrote on last edited by
              #6

              @engsml
              hi
              Its only sent to the widget under the mouse cursor.
              So yes, if you want to trap them there, you need to subclass and override that.
              However, if you need mouse info a global scope , maybe look into event filters.
              That allows to capture it across various Widgets without subclassing.
              If you already subclassed QChartView, override is ofcourse most easy.

              http://doc.qt.io/qt-5/eventsandfilters.html

              E 1 Reply Last reply
              0
              • mrjjM mrjj

                @engsml
                hi
                Its only sent to the widget under the mouse cursor.
                So yes, if you want to trap them there, you need to subclass and override that.
                However, if you need mouse info a global scope , maybe look into event filters.
                That allows to capture it across various Widgets without subclassing.
                If you already subclassed QChartView, override is ofcourse most easy.

                http://doc.qt.io/qt-5/eventsandfilters.html

                E Offline
                E Offline
                engsml
                wrote on last edited by
                #7

                @mrjj How would I subclass QChartView? I think that is what I am missing.

                mrjjM 1 Reply Last reply
                0
                • E engsml

                  @mrjj How would I subclass QChartView? I think that is what I am missing.

                  mrjjM Offline
                  mrjjM Offline
                  mrjj
                  Lifetime Qt Champion
                  wrote on last edited by mrjj
                  #8

                  hi

                  class MyQChartView : public QChartView {
                    Q_OBJECT
                   public:
                    explicit MyQChartView (QWidget* parent = 0) : QChartView(parent) {}
                    ~QChartView() {}
                  protected:
                   virtual void moveEvent(QMoveEvent* event) override {
                          .....
                   }
                  };
                  

                  If you have the QChartView in UI file, you can use promotion to easy replace it at runtime with your version.
                  http://doc.qt.io/qt-5/designer-using-custom-widgets.html
                  just give it MyQChartView as class name and MyQChartView .h (if you put it in own file)
                  else what ever .h file it lives in.

                  update: you might want to call base class version as it might use it.

                  virtual void moveEvent(QMoveEvent* event) override {
                          QChartView::moveEvent(event); // call base first
                  ...
                   }
                  
                  E 1 Reply Last reply
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                  • mrjjM Offline
                    mrjjM Offline
                    mrjj
                    Lifetime Qt Champion
                    wrote on last edited by
                    #9

                    updated code. paste error.
                    explicit QChartView (QWidget* parent = 0) : QChartView(parent) {}
                    --->
                    explicit MyQChartView (QWidget* parent = 0) : QChartView(parent) {}

                    1 Reply Last reply
                    0
                    • mrjjM mrjj

                      hi

                      class MyQChartView : public QChartView {
                        Q_OBJECT
                       public:
                        explicit MyQChartView (QWidget* parent = 0) : QChartView(parent) {}
                        ~QChartView() {}
                      protected:
                       virtual void moveEvent(QMoveEvent* event) override {
                              .....
                       }
                      };
                      

                      If you have the QChartView in UI file, you can use promotion to easy replace it at runtime with your version.
                      http://doc.qt.io/qt-5/designer-using-custom-widgets.html
                      just give it MyQChartView as class name and MyQChartView .h (if you put it in own file)
                      else what ever .h file it lives in.

                      update: you might want to call base class version as it might use it.

                      virtual void moveEvent(QMoveEvent* event) override {
                              QChartView::moveEvent(event); // call base first
                      ...
                       }
                      
                      E Offline
                      E Offline
                      engsml
                      wrote on last edited by
                      #10

                      @mrjj Thank you! Do I create another .cpp and header file and include this in my project?

                      mrjjM 1 Reply Last reply
                      0
                      • E engsml

                        @mrjj Thank you! Do I create another .cpp and header file and include this in my project?

                        mrjjM Offline
                        mrjjM Offline
                        mrjj
                        Lifetime Qt Champion
                        wrote on last edited by mrjj
                        #11

                        @engsml
                        Yes, that is the cleanest. (IMHO)
                        and then just promote it. ( it sounds complex but really easy after first time)

                        E 2 Replies Last reply
                        1
                        • mrjjM mrjj

                          @engsml
                          Yes, that is the cleanest. (IMHO)
                          and then just promote it. ( it sounds complex but really easy after first time)

                          E Offline
                          E Offline
                          engsml
                          wrote on last edited by
                          #12

                          @mrjj Thank you! I will try that

                          1 Reply Last reply
                          0
                          • mrjjM mrjj

                            @engsml
                            Yes, that is the cleanest. (IMHO)
                            and then just promote it. ( it sounds complex but really easy after first time)

                            E Offline
                            E Offline
                            engsml
                            wrote on last edited by
                            #13

                            @mrjj When I create the new class, what do I make the base class? Also, what does promoting accomplish in the sense that it overrides the QChartView class?

                            mrjjM 1 Reply Last reply
                            0
                            • E engsml

                              @mrjj When I create the new class, what do I make the base class? Also, what does promoting accomplish in the sense that it overrides the QChartView class?

                              mrjjM Offline
                              mrjjM Offline
                              mrjj
                              Lifetime Qt Champion
                              wrote on last edited by mrjj
                              #14

                              @engsml
                              just see code snippet ?
                              Like that. its complete override. with mousemove.

                              promotion is just easy way to get your type into the UI file.
                              Creator just note the actual type you want and at runtime, its your new widget instead.
                              Like a runtime replace.
                              if you insert the Chart via code, you have no use for promotion.

                              E 1 Reply Last reply
                              0
                              • mrjjM mrjj

                                @engsml
                                just see code snippet ?
                                Like that. its complete override. with mousemove.

                                promotion is just easy way to get your type into the UI file.
                                Creator just note the actual type you want and at runtime, its your new widget instead.
                                Like a runtime replace.
                                if you insert the Chart via code, you have no use for promotion.

                                E Offline
                                E Offline
                                engsml
                                wrote on last edited by
                                #15

                                @mrjj Hi. thanks for your help! I ended up not being able to figure it out, but am currently looking into the event filters option. I added QtCharts::QChartView::mouseMoveEvent(event); to my function to pass the event to the chartView but it still won't display any information when the mouse is on the plot. Any ideas? I'm following the "callout" example which has a similar structure.

                                1 Reply Last reply
                                0
                                • mrjjM Offline
                                  mrjjM Offline
                                  mrjj
                                  Lifetime Qt Champion
                                  wrote on last edited by mrjj
                                  #16

                                  Hi
                                  ah, QChartView is basically a QAbstractScrollArea which means it has the

                                  https://doc.qt.io/qt-5/qabstractscrollarea.html#viewport

                                  There is a high chance that this viewport objects uses/eats the mouseMove and hence the Widget dont see them
                                  or viewport have no mouse tracking.

                                  i might be able to test it tonight.

                                  Else event filter sounds like a plan. set it on viewport().

                                  1 Reply Last reply
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