I am creating a custom color picker by sub classing QFrame. There are three main functionality I would be needing.

1. A color picker
2. dragdrop color to other picker
3. right click menu

There won't be any problem in 1 and 3. How ever for 2 there are:

When you drop color to target, a menu appears with two options: swap & replace
If user select "swap", it should swap the colors of source and target
If user select "replace", it should replace the color of target with source.

drag & drop is having some problem:
Qt Code: 
  1. void DragWidget::dragEnterEvent(QDragEnterEvent *event)
  2. {
  3.     if (event->mimeData()->hasColor()) {
  4.         if (event->source() == this) {
  5.             event->setDropAction(Qt::MoveAction);
  6.             event->accept();
  7.         }
  8.         else {
  9.             event->acceptProposedAction();
  10.         }
  11.     }
  12.     else {
  13.         event->ignore();
  14.     }
  15.  }
  16.  
  17. void DragWidget::dragMoveEvent(QDragMoveEvent *event)
  18. {
  19.     if (event->mimeData()->hasColor()) {
  20.         if (event->source() == this) {
  21.             event->setDropAction(Qt::MoveAction);
  22.             event->accept();
  23.         }
  24.         else {
  25.             event->acceptProposedAction();
  26.         }
  27.     }
  28.     else {
  29.         event->ignore();
  30.     }
  31.  
  32. }
  33.  
  34. void DragWidget::dropEvent(QDropEvent *event)
  35. {
  36.     if (event->mimeData()->hasColor()) {
  37.         myColor = qvariant_cast<QColor>(event->mimeData()->colorData());
  38.  
  39.         if (event->source() == this) {
  40.             event->setDropAction(Qt::MoveAction);
  41.             event->accept();
  42.         } else {
  43.             event->acceptProposedAction();
  44.         }
  45.     } else {
  46.         event->ignore();
  47.     }
  48. }
  49.  
  50.  
  51. void DragWidget::mousePressEvent(QMouseEvent *event)
  52. {
  53.     QMimeData *mimeData = new QMimeData;
  54.     mimeData->setColorData(QVariant(myColor));
  55.  
  56.     QDrag *drag = new QDrag(this);
  57.     drag->setMimeData(mimeData);
  58. }
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