Question

I’m writing a diagram editor in Qt with Graphics View Framework.
Currently I’m just trying to create a simple Node (QGraphicsItem) on GraphScene (QGraphicsScene). I created a Canvas (QGraphicsView) and added a grid to it. I can even add Nodes and move them around on scene. My final goal is to have different working modes, editing and styling options, etc. For now I just want to know how can I setup selection for Nodes already present on scene. I tried doing it with mouse events but noticed that event calls for selection and Node insertion overlap… When I try to select something a new Node is created… This is my first Qt application so I don’t fully understand how the functionality I want to achieve should be designed.

How the Selection Rectangle should be properly drawn?
How should I manage mouse events that conflict with each other?

Answer 1

• You can use a checkable button/action(that’s a QPushButton/QAction with a checkable property set to ‘true) to switch between Edit & Insert mode. Then you check the state in your mouse event and insert a new item only if you’re in Insertion mode.
• You can also distinct between mouse buttons – insert item when dragged with the right button for example
• Or use QKeyboardModifiers – for example: on drag + Ctrl – insert item.

Hope this helps.