What design pattern shall I use

Some indirect inputs that may be useful


Basically a chart is composed of
 -  An X- axis
 -  A Y- axis
 -  Or No Axis (Pie chart and others)
 -   Has a Title
 -   Has Legends
 -   Different renderings (bar, column, pie, candle-stick etc).
 -   Has model or data to bind to
 -   et el

If you analyze this you may observe that the only changing part in this is the rendering, i.e. a line chart, a pie chart etc rest other things are composable or in other words you may thing it this way...

A chart  has
-   a data to bind to
-   Render as

And is decorated with a 
- Title
- Axis
- Legends 
etc.


So, you can create various decorators for these elements and compose your main chart with these decorators at runtime and as and when required.

Approach 1 - Decorator pattern

The higher level API could be something like this

// Create a chart with legends
Chart lineChart = new LineChart();
ln.DataSource =  "Your datasource here";
lineChart.Render();   // Renders the linechart without legend

LegendsChart  ln = new LegendsChart(lineChart);

ln.Render();   // Renders the line chart with legends as well

Refer Decorator patterns here  http://www.dofactory.com/Patterns/PatternDecorator.aspx
You can add more decorators as needed without modifying your existing code


Approach 2 - Fluent API
It will look something like this
Chart lineChart  = new Linechart().ShowLegend();
linChartDataSource = "Your datasource here";
lineChart.Render();

lineChart.AddBorder();
lineChart.Render();

A good example of fluent interface can be found here.. http://weblogs.asp.net/jgalloway/archive/2006/12/06/a-simple-example-of-a-fluent-interface.aspx



NOTE:  This is just couple of  approaches, you an find numerous other approaches as well