How to refresh Unreal Editor Viewport when dragging a spinbox (FModeToolkit)?

Question

The viewport of my custom EdMode does not update while I drag a spinbox (which is in a custom FModeToolkit). In fact, MyCustomEdMode::Render() is not even called (while the spinbox).

How can I refresh the viewport while dragging?

Answer 1

The MyCustomEdMode::::DrawHUD(FEditorViewportClient* ViewportClient, FViewport* Viewport, const FSceneView* View, FCanvas* Canvas) function gives access to the FEditorViewportClient which must be invalidated.

In the spinbox onValueChange callback there must be ViewportClient->Invalidate();.