Synchronized scrolling of two ScrollViewers whenever any one is scrolled in wpf

Question

I have gone through the thread:

binding two VerticalScrollBars one to another

it has almost helped to achieve the goal but still there is something missing.

Answer 1

Well, I made an implementation based on https://www.codeproject.com/Articles/39244/Scroll-Synchronization but it's I think neater.

There's a synchronised scroll token that holds references to the things to scroll. Then there's the attached property that is separate. I haven't figured out how to unregister because the reference remains - so I left that unimplemented.

Eh, here goes:

public class SynchronisedScroll
{

    public static SynchronisedScrollToken GetToken(ScrollViewer obj)
    {
        return (SynchronisedScrollToken)obj.GetValue(TokenProperty);
    }
    public static void SetToken(ScrollViewer obj, SynchronisedScrollToken value)
    {
        obj.SetValue(TokenProperty, value);
    }
    public static readonly DependencyProperty TokenProperty =
        DependencyProperty.RegisterAttached("Token", typeof(SynchronisedScrollToken), typeof(SynchronisedScroll), new PropertyMetadata(TokenChanged));

    private static void TokenChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
    {
        var scroll = d as ScrollViewer;
        var oldToken = e.OldValue as SynchronisedScrollToken;
        var newToken = e.NewValue as SynchronisedScrollToken;

        if (scroll != null)
        {
            oldToken?.unregister(scroll);
            newToken?.register(scroll);
        }
    }
}

and the other bit

public class SynchronisedScrollToken
{
    List registeredScrolls = new List();

    internal void unregister(ScrollViewer scroll)
    {
        throw new NotImplementedException();
    }

    internal void register(ScrollViewer scroll)
    {
        scroll.ScrollChanged += ScrollChanged;
        registeredScrolls.Add(scroll);
    }

    private void ScrollChanged(object sender, ScrollChangedEventArgs e)
    {
        var sendingScroll = sender as ScrollViewer;
        foreach (var potentialScroll in registeredScrolls)
        {
            if (potentialScroll == sendingScroll)
                continue;

            if (potentialScroll.VerticalOffset != sendingScroll.VerticalOffset)
                potentialScroll.ScrollToVerticalOffset(sendingScroll.VerticalOffset);

            if (potentialScroll.HorizontalOffset != sendingScroll.HorizontalOffset)
                potentialScroll.ScrollToHorizontalOffset(sendingScroll.HorizontalOffset);
        }
    }
}

Use by defining a token in some resource accessible to all the things that need to be scroll synchronised.

And then use it wherever you need it by:

I've only tested it when scrolling vertically and it works for me.