keybindings for rollover functionality | Fast, Native Chart Controls for WPF, iOS, Android and Xamarin

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Answered

Hello support team,

Im looking for a way to use keys to navigate through values in the graph. The rollover provides this easily with the mouse.
I include the rollovermodifier and the template I have. Do you have an idea how to do this? I just need to navigate left and right with the cursors. Any input or idea is extremely welcome.
Thank you very much for your great support

Marcel

WPF

Marcel asked 6 years ago

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Answers (1)

Best Answer

Hi Marcel,

Keyboard input for ChartModifiers is a hotly requested feature. We haven’t implemented this yet, but you can achieve the same effect by a workaround.

Start by inheriting RolloverModifier and subscribing to the KeyDown event of the parent Window. E.g.

public class KeydownRolloverModifier : RolloverModifier
{
    private double positionFraction = 0.0;

    void KeydownRolloverModifier_PreviewKeyDown(object sender, KeyEventArgs e)
    {
        if (e.Key == Key.Right)
        {
            positionFraction += 0.01;
        }
        if (e.Key == Key.Left)
        {
            positionFraction -= 0.01;
        }

        // Constrain to 0.0, 1.0
        positionFraction = positionFraction > 1.0 ? 1.0 : positionFraction < 0.0 ? 0.0 : positionFraction;

        UpdateRollover(positionFraction);
    }

    public override void OnAttached()
    {
        base.OnAttached();
        var scichart = (ParentSurface as SciChartSurface);
        scichart.FindLogicalParent<Window>().PreviewKeyDown +=
            new KeyEventHandler(KeydownRolloverModifier_PreviewKeyDown);
    }

    public override void OnModifierMouseMove(ModifierMouseArgs e)
    {
        // Don't call base. This way the mouse does not change the cursor position
        // base.OnModifierMouseMove(e);
    }

    private void UpdateRollover(double fraction)
    {
        var point = new Point(ModifierSurface.Width * fraction, 0);
        point = ModifierSurface.TranslatePoint(point, RootGrid);
        base.OnModifierMouseMove(new ModifierMouseArgs(point, MouseButtons.None, MouseModifier.None, true));
    }
}

The code for FindLogicalParent is as follows:

public static class FrameworkElementExtensions
{
    public static T FindLogicalParent<T>(this FrameworkElement element) where T : FrameworkElement
    {
        var parent = (FrameworkElement)element.Parent;

        if (parent is T)
            return (T)parent;

        return parent.FindLogicalParent<T>();
    }
}

Using the above you should get a key right/left response by moving the rollover. It’ll move by a percentage each time, not to the next data-point. If you wish to achieve data-point by point moves, then maybe take a look at the HitTest API (BaseRenderableSeries.HitTest). This is used in the base RolloverModifier class to get the X,Y values of data-points.