Adjusting Mouse Wheel Scroll Step in SyntaxEditor for UI for WinForms

Environment

Product Version	Product	Author
2025.2.520	RadSyntaxEditor for WinForms	Dinko Krastev

Description

There could be a scenario in which the mouse wheel speed needs to be per user preferences. However, the control does not provide a way to manipulate the scroll step. In this KB article, we will demonstrate how, using custom code, we could manipulate the scroll speed.

Solution

To adjust the mouse wheel scroll step, create a custom class that inherits from RadSyntaxEditor and override the OnMouseWheel method. Modify the Value property of the VerticalScrollBarElement and the VerticalScrollOffset of the SyntaxEditorPresenter. The last step is to set the VerticalScrollOffset property. This property is not public and we will need to use reflection to set it. Below is a sample implementation:

public class MySyntax : RadSyntaxEditor
{
    protected override void CreateChildItems(RadElement parent)
    {
        base.CreateChildItems(parent);
    }

    protected override void OnMouseWheel(MouseEventArgs e)
    {
        // Access and update scrolling properties
        System.Reflection.PropertyInfo pi = typeof(SyntaxEditorPresenter).GetProperty(
            "VerticalScrollOffset", 
            System.Reflection.BindingFlags.Instance | System.Reflection.BindingFlags.Public
        );

        if (e.Delta < 0) // Scroll down
        {
            this.SyntaxEditorElement.VerticalScrollBar.Value += this.SyntaxEditorElement.VerticalScrollBar.SmallChange;
            pi.SetValue(this.SyntaxEditorElement.EditorPresenter, this.SyntaxEditorElement.VerticalScrollBar.Value);
        }
        else // Scroll up
        {
            this.SyntaxEditorElement.VerticalScrollBar.Value -= this.SyntaxEditorElement.VerticalScrollBar.SmallChange;
            pi.SetValue(this.SyntaxEditorElement.EditorPresenter, this.SyntaxEditorElement.VerticalScrollBar.Value);
        }

        this.SyntaxEditorElement.EditorPresenter.InvalidateLayout(false);
    }
    public override string ThemeClassName
    {
        get
        {
            return typeof(RadSyntaxEditor).FullName;
        }
    }
}

Steps:

1. Create a new class that inherits RadSyntaxEditor.
   
2. Override the OnMouseWheel method.
   
3. Use reflection to access and modify the VerticalScrollOffset property of SyntaxEditorPresenter.
   
4. Update the Value property of VerticalScrollBarElement based on the mouse wheel scroll direction.
   
5. Test the custom implementation by adding it to your application.

See Also

• RadSyntaxEditor Documentation