Extension Methods for Navigating the xamDataChart

I recently posted a video demonstrating how to implement some extension methods to support xamDataChart navigation. The navigation support implemented in the demo included:

• PanUp
• PanDown
• PanLeft
• PanRight
• ZoomIn
• ZoomOut
• FitInWindow

The only problem with the code I used in the video, was that the event handler for the buttons included a long if statement to handle navigation support. As the famous quote goes, “If it smells, it’s bad code”, so I wanted to refactor the implementation to be a bit more maintainable. Before I get into the changes, I first want to list the extension methods that I implemented in order to make it easy to pan and zoom the chart. Notice that the methods us a default scale value so you are not required to pass in a scale amount for each method call.

public static class xamDataChartExtensions
{
    private static double _defaultScale = 0.05;

    public static void ZoomIn(this XamDataChart dataChart)
    {
        ZoomIn(dataChart, _defaultScale);
    }

    public static void ZoomIn(this XamDataChart dataChart, double scale)
    {
        dataChart.WindowScaleHorizontal -= scale;
        dataChart.WindowScaleVertical -= scale;
    }

    public static void ZoomOut(this XamDataChart dataChart)
    {
        ZoomOut(dataChart, _defaultScale);
    }

    public static void ZoomOut(this XamDataChart dataChart, double scale)
    {
        dataChart.WindowScaleHorizontal += scale;
        dataChart.WindowScaleVertical += scale;
    }

    public static void PanUp(this XamDataChart dataChart)
    {
        PanUp(dataChart, _defaultScale);
    }

    public static void PanUp(this XamDataChart dataChart, double scale)
    {
        dataChart.WindowPositionVertical -= scale;
    }

    public static void PanDown(this XamDataChart dataChart)
    {
        PanDown(dataChart, _defaultScale);
    }

    public static void PanDown(this XamDataChart dataChart, double scale)
    {
        dataChart.WindowPositionVertical += scale;
    }

    public static void PanLeft(this XamDataChart dataChart)
    {
        PanLeft(dataChart, _defaultScale);
    }

    public static void PanLeft(this XamDataChart dataChart, double scale)
    {
        dataChart.WindowPositionHorizontal -= scale;
    }

    public static void PanRight(this XamDataChart dataChart)
    {
        PanRight(dataChart, _defaultScale);
    }

    public static void PanRight(this XamDataChart dataChart, double scale)
    {
        dataChart.WindowPositionHorizontal += scale;
    }

The previous code I implemented featured a nested if statement that would call the appropriate extension method, but I knew there was an easy way to clean this code out of the page. The key to a more concise approach begins by defining a enumeration which lists the navigation options:

public enum xamDataChartNavigationTypes
{ 
    PanUp,
    PanDown,
    PanLeft,
    PanRight,
    ZoomIn,
    ZoomOut,
    FitInWindow,
    Undefined
}

Now armed with the navigation enumeration I added another extension method named Navigate which takes an instance of the navigation enumeration and an option to pass an explicit scale value:

    public static void Navigate(this XamDataChart dataChart, xamDataChartNavigationTypes navigationType)
    {
        Navigate(dataChart, navigationType, _defaultScale);
    }

    public static void Navigate(this XamDataChart dataChart, xamDataChartNavigationTypes navigationType, double scale)
    {
        switch (navigationType)
        {
            case xamDataChartNavigationTypes.FitInWindow:
                dataChart.WindowRect = new Rect(0, 0, 1, 1);
                break;
            case xamDataChartNavigationTypes.PanUp:
                dataChart.PanUp(scale);
                break;
            case xamDataChartNavigationTypes.PanDown:
                dataChart.PanDown(scale);
                break;
            case xamDataChartNavigationTypes.PanLeft:
                dataChart.PanLeft(scale);
                break;
            case xamDataChartNavigationTypes.PanRight:
                dataChart.PanRight(scale);
                break;
            case xamDataChartNavigationTypes.ZoomIn:
                dataChart.ZoomIn(scale);
                break;
            case xamDataChartNavigationTypes.ZoomOut:
                dataChart.ZoomOut(scale);
                break;
            default:
                break;
        }
    }

Now as long at the Tag property of your button is equal to one of the navigation enumeration values (ex: PanUp, PanDown, etc), then the click handler is reduced to the following:

private void Navigate_Click(object sender, RoutedEventArgs e)
{
    string tag = (sender as Button).Tag.ToString();
    xamDataChartNavigationTypes navigationType;

    if (xamDataChartNavigationTypes.TryParse(tag, out navigationType))
    {
        this.dataChart.Navigate(navigationType);
    }
}