Access to the underlying .NET chart object (#102)

* Exposed access to the underlying
 System.Windows.Forms.DataVisualization.Charting.Chart object via a
 "visitor"-esque member method ApplyToChart(...), in order to enable
 programmatic control over the chart form window (which is already accessible
 to the user manually via the Properties tab of the chart form). This enables
 us to use charting with the following example pattern:

let inputData = [1;2;3]
inputData
|> Chart.Line
|> fun c      -> c.WithLegend()  // add legend using the existing method
|> fun c      -> ( c, c.ShowChart() )    // create the chart form
|> fun (c, _) -> (c, c.ApplyToChart( fun c -> c.ChartAreas.[0].CursorX.IsUserSelectionEnabled <- true ) )   // can now modify chart form using all of the available .NET Chart API by chaining lines like this one
|> ignore   // avoid displaying the chart twice

* ApplyToChart() now returns the Chart object, enabling us to chain calls, like in the example below:

inputData
|> Chart.Line
// do things necessary before chart is rendered
|> fun c -> c.WithLegend( FontSize = 5.0 )
             .WithStyling( Color = System.Drawing.Color.Red )
// create the chart form and render the chart
|> fun c -> ( c, c.ShowChart() )
// do things that can only be done after the chart is rendered
|> fun ( c, _ ) -> c.ApplyToChart( fun c -> c.ChartAreas.[0].CursorX.IsUserSelectionEnabled <- true )
                    .ApplyToChart( fun c -> c.ChartAreas.[0].CursorY.IsUserSelectionEnabled <- true )
|> ignore  // avoid displaying the chart twice

* Implemented the "caching" of functions applid using ApplytoChart() until the point of drawing of the actual chart, as discussed in #102 (comment). ApplyToChart() is now usable with the existing simple dot-notation.

* Added ApplyToChart to the documentation.

* CustomizationFunctions need to be applied in the order they were added, if only for the sake of clarity. This was noticed by @simra.

docs/content/FurtherSamples.fsx

@@ -188,4 +188,17 @@ Chart.Line(data,Name="SomeData").WithDataPointLabels(PointToolTip="Hello, I am #
 Chart.Stock(timeHighLowOpenClose)
 Chart.ThreeLineBreak(data,Name="SomeData").WithDataPointLabels(PointToolTip="Hello, I am #SERIESNAME") 
 
-Chart.Histogram([for x in 1 .. 100 -> rand()*10.],LowerBound=0.,UpperBound=10.,Intervals=10.)
+Chart.Histogram([for x in 1 .. 100 -> rand()*10.],LowerBound=0.,UpperBound=10.,Intervals=10.)
+
+// Example of .ApplyToChart() used to alter the settings on the window chart and to access the chart child objects.
+// This can normally be done manually, in the chart property grid (right click the chart, then "Show Property Grid"). 
+// This is useful when you want to try out carious settings first. But once you know what you want, .ApplyToChart() 
+// allows programmatic access to the window properties. The two examples below are: IsUserSelectionEnabled essentially 
+// allows zooming in and out along the given axes, and the longer fiddly example below does the same work as .WithDataPointLabels() 
+// but across all series objects.
+[ Chart.Column(data); 
+  Chart.Column(data2) |> Chart.WithSeries.AxisType( YAxisType = Windows.Forms.DataVisualization.Charting.AxisType.Secondary ) ]
+|> Chart.Combine
+|> fun c -> c.WithLegend()
+             .ApplyToChart( fun c -> c.ChartAreas.[0].CursorX.IsUserSelectionEnabled <- true )
+             .ApplyToChart( fun c -> let _ = [0 .. c.Series.Count-1] |> List.map ( fun s -> c.Series.[ s ].ToolTip <- "#SERIESNAME (#VALX, #VAL{0:00000})" ) in () )

docs/content/fsharpcharting.md

@@ -41,7 +41,7 @@ The following methods are used to style chart objects:
  * `WithTitle`
  * `WithXAxis`
  * `WithYAxis`
-
+ * `ApplyToChart`
 
 Please [contribute](contributing.html) more documentation on the following topics:
 

src/FSharp.Charting.fs

@@ -1145,6 +1145,7 @@ namespace FSharp.Charting
 
             let mutable data = ChartData.Values (NotifySeq.ignoreReset (NotifySeq.notifyOrOnce []), ChartValueType.Auto, "Item1", "Item2", "") 
             let mutable margin = DefaultMarginForEachChart
+            let mutable customizationFunctions : (Chart -> unit) list = []
 
             [<Obsolete("This type does not support GetHashCode()")>]
             override x.GetHashCode() = 0
@@ -1165,6 +1166,11 @@ namespace FSharp.Charting
             member internal x.Chart with get() = chart.Value and set v = chart <- evalLazy v
             member internal x.Margin with get() = margin and set v = margin <- v
             member internal x.Name with get() = name and set v = name <- v
+            member internal x.CustomizationFunctions with get() = customizationFunctions
+
+            member x.ApplyToChart ( fn : Chart -> unit ) =
+                customizationFunctions <- ( fn :: customizationFunctions )
+                x
 
             /// Ensure the chart has a Title
             member internal x.ForceTitle() = 
@@ -3944,6 +3950,7 @@ namespace FSharp.Charting
                 frm.Text <- ProvideTitle ch
                 frm.Controls.Add(ctl)
                 frm.Show()
+                ch.CustomizationFunctions |> List.rev |> List.map (fun fn -> fn ch.Chart) |> ignore
                 ctl.Focus() |> ignore
                 frm