Question

Due to an unsolved issue in my current project [ Weird scrollbar UI in hosted WPF composite control ], I’ve had to defer to workarounds. One such idea I came up with was to keep the ScrollViewer in question in sync with a Windows Forms ScrollBar (horizontal and vertical). How would I go about doing that?

In essence, I want the WinForms scrollbar(s) to work like the ScrollViewers (in terms of dragging and events suchlike).

Answer 1

I managed to implement it without having to much around with the WinAPI. Here’s how I did it:

1. Registered a ScrollOffsetChanged event handler with the scrollviewer (the composite control that implemented the IScrollInfo interface exposed the event).
2. Registered a ValueChanged event handler with the windows forms scrollbar.
3. A couple of signal flags to prevent cyclic calls to the event handler.
4. The first handler called an UpdateExternalScrollBars() function that calculated the Maximium Scrollbar property using the following expression: ScrollViewer->ExtentHeight/Width – ScrollViewer->ViewportHeight/Width. The Value property was directly set to ScrollViewer->Vertical/HorizontalOffset.
5. The second fetched the Value property from the windows forms scrollbar and passed it to ScrolViewer->ScrollToVertial/HorizontalOffset(). The signal flags were appropriately set beforehand.