Sorting plot legend?

[StefanK]

Hello

I would like to sort my plot legend alphabetically. Therefore I imlemented following class inheriting from QwtLegend assuming that the virtual legendItems(void) method is called by the plot.

class Legend : public QwtLegend
{
   public:
      Legend(QWidget* pParent = 0) : QwtLegend(pParent)
      {   
      }
 
      QList<QWidget*> legendItems(void) const
      {
         QList<QWidget*> lLegendItems = QwtLegend::legendItems();
         qSort(lLegendItems.begin(), lLegendItems.end(), Legend::lessThan);
         return lLegendItems;
      }
 
      static bool lessThan(QWidget* pLi1, QWidget* pLi2)
      {
         if(pLi1 && pLi2)
         {
            if (pLi1->inherits("QwtLegendItem") && pLi2->inherits("QwtLegendItem"))
            {
               QwtLegendItem* lLabel1 = (QwtLegendItem*)pLi1;
               QwtLegendItem* lLabel2 = (QwtLegendItem*)pLi2;
               return lLabel1->text().text().toLower() < lLabel2->text().text().toLower();
            }
         }
         return false;
      }
};

class Legend : public QwtLegend
{
   public:
      Legend(QWidget* pParent = 0) : QwtLegend(pParent)
      {   
      }
      
      QList<QWidget*> legendItems(void) const
      {
         QList<QWidget*> lLegendItems = QwtLegend::legendItems();
         qSort(lLegendItems.begin(), lLegendItems.end(), Legend::lessThan);
         return lLegendItems;
      }
      
      static bool lessThan(QWidget* pLi1, QWidget* pLi2)
      {
         if(pLi1 && pLi2)
         {
            if (pLi1->inherits("QwtLegendItem") && pLi2->inherits("QwtLegendItem"))
            {
               QwtLegendItem* lLabel1 = (QwtLegendItem*)pLi1;
               QwtLegendItem* lLabel2 = (QwtLegendItem*)pLi2;
               return lLabel1->text().text().toLower() < lLabel2->text().text().toLower();
            }
         }
         return false;
      }
};

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The legend is added to the plot...

Legend* lLegend = new Legend(mPlot->canvas());
// some initialisations...
mPlot->insertLegend(lLegend, QwtPlot::ExternalLegend);

Legend* lLegend = new Legend(mPlot->canvas());
// some initialisations...
mPlot->insertLegend(lLegend, QwtPlot::ExternalLegend);

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But the legendItems(void) method is never called.
Any idea what's wrong?

Best Regards
Stefan

[StefanK]

The only way I found, was to create the curves and to add them to the plot already sorted alphabetically by title.

Best Regards
Stefan

[Uwe]

The legend items are organized in a QLayout. So its order depends on the order they are inserted. If you want to reorder them you have to remove and reinsert them ( like you have found out yourself ).

But instead of recreating your curves you could also detach/attach them - or best unset/set the QwtPlotItem::Legend flag.

Uwe