Using F#, WPF, FsXaml, a Menu, and a Dialog Box

Introduction

The goal here is to build a simple application in F# using the Windows Presentation Foundation (WPF) with traditional menus and dialog boxes. It stems from my frustration in trying to wade through hundreds of sections of documentation, articles and posts dealing with F# and WPF. In order to do anything with WPF, you seem to have to know everything about it. My purpose here is to provide a possible way in, a simple desktop project that can serve as a template for your apps.

Add the "Business Logic"

Presumably, your program will do something. Add your working code to the project in place of Program.fs. In this case, our task is to draw spirograph curves on a Window Canvas. This is accomplished using Spirograph.fs, below.

namespace Spirograph

// open System.Windows does not automatically open all its sub-modules, so we 
// have to open them explicitly as below, to get the resources noted for each.
open System                             // for Math.PI
open System.Windows                     // for Point
open System.Windows.Controls            // for Canvas
open System.Windows.Shapes              // for Ellipse
open System.Windows.Media               // for Brushes

// ------------------------------------------------------------------------------
// This file is first in the build sequence, so types should be defined here
type DialogBoxXaml  = FsXaml.XAML<"DialogBox.xaml">
type MainWindowXaml = FsXaml.XAML<"MainWindow.xaml">
type App            = FsXaml.XAML<"App.xaml"> 

// ------------------------------------------------------------------------------
// Model: This draws the Spirograph
type MColor = | MBlue   | MRed | MRandom

type Model() =
  let mutable myCanvas: Canvas = null
  let mutable myR              = 220    // outer circle radius
  let mutable myr              = 65     // inner circle radius
  let mutable myl              = 0.8    // pen position relative to inner circle
  let mutable myColor          = MBlue  // pen color
  
  let rng                      = new Random()
  let mutable myRandomColor    = Color.FromRgb(rng.Next(0, 255) |> byte,
                                               rng.Next(0, 255) |> byte,
                                               rng.Next(0, 255) |> byte)

  member this.MyCanvas
    with get() = myCanvas
    and  set(newCanvas) = myCanvas <- newCanvas

  member this.MyR
    with get() = myR
    and  set(newR) = myR <- newR

  member this.Myr
    with get() = myr
    and  set(newr) = myr <- newr

  member this.Myl
    with get() = myl
    and  set(newl) = myl <- newl

  member this.MyColor
    with get() = myColor
    and  set(newColor) = myColor <- newColor

  member this.Randomize =
    // Here we randomize the parameters. You can play with the possible ranges of
    // the parameters to find randomized spirographs that are pleasing to you.
    this.MyR      <- rng.Next(100, 500)
    this.Myr      <- rng.Next(this.MyR / 10, (9 * this.MyR) / 10)
    this.Myl      <- 0.1 + 0.8 * rng.NextDouble()
    this.MyColor  <- MRandom
    myRandomColor <- Color.FromRgb(rng.Next(0, 255) |> byte,
                                   rng.Next(0, 255) |> byte,
                                   rng.Next(0, 255) |> byte)

  member this.DrawSpirograph =
    // Draw a spirograph. Note there is some fussing with ints and floats; this 
    // is required because the outer and inner circle radii are integers. This is
    // necessary in order for the spirograph to return to its starting point 
    // after a certain number of revolutions of the outer circle.
    
    // Start with usual recursive gcd function and determine the gcd of the inner
    // and outer circle radii. Everything here should be in integers.
    let rec gcd x y =
        if y = 0 then x
        else gcd y (x % y)
  
    let g = gcd this.MyR this.Myr             // find greatest common divisor
    let maxRev = this.Myr / g                 // maximum revs to repeat

    // Determine width and height of window, location of center point, scaling 
    // factor so that spirograph fits within the window, ratio of inner and outer
    // radii.
    
    // Everything from this point down should be float.
    let width, height = myCanvas.ActualWidth, myCanvas.ActualHeight
    let cx, cy = width / 2.0, height / 2.0    // coordinates of center point
    let maxR   = min cx cy                    // maximum radius of outer circle
    let scale  = maxR / float(this.MyR)             // scaling factor
    let rRatio = float(this.Myr) / float(this.MyR)  // ratio of the radii

    // Build the collection of spirograph points, scaled to the window.
    let points = new PointCollection()
    for degrees in [0 .. 5 .. 360 * maxRev] do
      let angle = float(degrees) * Math.PI / 180.0
      let x, y = cx + scale * float(this.MyR) *
                 ((1.0-rRatio)*Math.Cos(angle) +
                  this.Myl*rRatio*Math.Cos((1.0-rRatio)*angle/rRatio)),
                 cy + scale * float(this.MyR) *
                 ((1.0-rRatio)*Math.Sin(angle) - 
                  this.Myl*rRatio*Math.Sin((1.0-rRatio)*angle/rRatio))
      points.Add(new Point(x, y))
  
    // Create the Polyline with the above PointCollection, erase the Canvas, and 
    // add the Polyline to the Canvas Children
    let brush = match this.MyColor with
                | MBlue   -> Brushes.Blue
                | MRed    -> Brushes.Red
                | MRandom -> new SolidColorBrush(myRandomColor)
  
    let mySpirograph = new Polyline()
    mySpirograph.Points <- points
    mySpirograph.Stroke <- brush

    myCanvas.Children.Clear()
    this.MyCanvas.Children.Add(mySpirograph) |> ignore

Spirograph.fs is the first F# file in the compilation order, so it contains the definitions of the types we will need. Its job is to draw a spirograph on the main window Canvas based on parameters entered in a dialog box. Since there are lots of references on how to draw a spirograph, we won't go into that here.

Add the App.xaml and App.xaml.fs to tie everything together

<!-- All boilerplate for now -->
<Application 
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"               
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml">      
    <Application.Resources>      
    </Application.Resources>  
</Application>

Here's the code behind:

namespace Spirograph

open System  
open System.Windows 
open System.Windows.Controls

module Main = 
  [<STAThread; EntryPoint>]
  let main _ =
    // Create the app and the model with the "business logic", then create the
    // main window and link its Canvas to the model so the model can access it.
    // The main window is linked to the app in the Run() command in the last line.
    let app = App()
    let model = new Model()
    let mainWindow = new MainWindow(app, model) 
    model.MyCanvas <- (mainWindow.FindName("myCanvas") :?> Canvas)         
    
    // Make sure the window is on top, and set its size to 2/3 of the dimensions 
    // of the screen.
    mainWindow.Topmost <- true
    mainWindow.Height  <- 
      (System.Windows.SystemParameters.PrimaryScreenHeight * 0.67)
    mainWindow.Width   <- 
      (System.Windows.SystemParameters.PrimaryScreenWidth * 0.67) 
    
    app.Run(mainWindow) // Returns application's exit code.

App.xaml is all boilerplate here, mainly to show where application resources, such as icons, graphics, or external files - can be declared. The companion App.xaml.fs pulls together the Model and the MainWindow, sizes the MainWindow to two-thirds of the available screen size, and runs it.

When you build this, remember to make sure that the Build property for each xaml file is set to Resource. Then you can either run through the debugger or compile to an exe file. Note that you cannot run this using the F# interpreter: The FsXaml package and the interpreter are incompatible.

There you have it. I hope you can use this as a starting point for your own applications, and in doing so you can extend your knowlege beyond what is shown here. Any comments and suggestions will be appreciated.

Add the code behind for MainWindow.xaml

namespace Spirograph

type MainWindow(app: App, model: Model) as this =
  inherit MainWindowXaml()

  let myApp   = app
  let myModel = model
  
  let whenLoaded _ =
    ()
  
  let whenClosing _ =
    ()
  
  let whenClosed _ =
    () 
  
  let menuExitHandler _ = 
    System.Windows.MessageBox.Show("Good-bye", "Spirograph") |> ignore
    myApp.Shutdown()
    () 
  
  let menuParametersHandler _ = 
    let myParametersDialog = new DialogBox(myApp, myModel, this)
    myParametersDialog.Topmost <- true
    let bResult = myParametersDialog.ShowDialog()
    myModel.DrawSpirograph
    () 
  
  let menuDrawHandler _ = 
    if myModel.MyColor = MRandom then myModel.Randomize
    myModel.DrawSpirograph
    () 
  
  let menuAboutHandler _ = 
    System.Windows.MessageBox.Show("F#/WPF Menus & Dialogs", "Spirograph") 
    |> ignore
    () 
  
  do          
    this.Loaded.Add whenLoaded
    this.Closing.Add whenClosing
    this.Closed.Add whenClosed
    this.menuExit.Click.Add menuExitHandler
    this.menuParameters.Click.Add menuParametersHandler
    this.menuDraw.Click.Add menuDrawHandler
    this.menuAbout.Click.Add menuAboutHandler

There's not a lot going on here: We open the Parameters dialog box when required and we have the option of redrawing the spirograph with whatever the current parameters are.

Create the dialog box in XAML and F#

The XAML file for the spirograph parameters is below. It includes three text boxes for the spirograph parameters and a group of three radio buttons for color. When we give radio buttons the same group name - as we have here - WPF handles the on/off switching when one is selected.

<!-- This first part is boilerplate, except for the title, height and width.
     Note that some fussing with alignment and margins may be required to get
     the box looking the way you want it. -->
<Window xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        Title="Parameters" Height="200" Width="250">
    <!-- Here we define a layout of 3 rows and 2 columns below the title bar -->
    <Grid>
        <Grid.RowDefinitions>
            <RowDefinition/>
            <RowDefinition/>
            <RowDefinition/>
            <RowDefinition/>
            <RowDefinition/>
        </Grid.RowDefinitions>
        <Grid.ColumnDefinitions>
            <ColumnDefinition/>
            <ColumnDefinition/>
        </Grid.ColumnDefinitions>
        <!-- Define a label and a text box for the first three rows. Top row is
             the integer radius of the outer circle -->
        <StackPanel Orientation="Horizontal" Grid.Column="0" Grid.Row="0" 
                    Grid.ColumnSpan="2">
            <Label VerticalAlignment="Top" Margin="5,6,0,1" Content="R: Outer" 
                   Height="24" Width='65'/>
            <TextBox x:Name="radiusR"  Margin="0,0,0,0.5" Width="120" 
                     VerticalAlignment="Bottom" Height="20">Integer</TextBox>
        </StackPanel>
        <!-- This defines a label and text box for the integer radius of the
             inner circle -->
        <StackPanel Orientation="Horizontal" Grid.Column="0" Grid.Row="1" 
                    Grid.ColumnSpan="2">
            <Label VerticalAlignment="Top" Margin="5,6,0,1" Content="r: Inner" 
                   Height="24" Width='65'/>
            <TextBox x:Name="radiusr"  Margin="0,0,0,0.5" Width="120" 
                     VerticalAlignment="Bottom" Height="20" Text="Integer"/>
        </StackPanel>
        <!-- This defines a label and text box for the float ratio of the inner
             circle radius at which the pen is positioned -->
        <StackPanel Orientation="Horizontal" Grid.Column="0" Grid.Row="2" 
                    Grid.ColumnSpan="2">
            <Label VerticalAlignment="Top" Margin="5,6,0,1" Content="l: Ratio" 
                   Height="24" Width='65'/>
            <TextBox x:Name="ratiol"  Margin="0,0,0,1" Width="120" 
                     VerticalAlignment="Bottom" Height="20" Text="Float"/>
        </StackPanel>
        <!-- This defines a radio button group to select color -->
        <StackPanel Orientation="Horizontal" Grid.Column="0" Grid.Row="3" 
                    Grid.ColumnSpan="2">
            <Label VerticalAlignment="Top" Margin="5,6,4,5.333" Content="Color" 
                   Height="24"/>
            <RadioButton x:Name="buttonBlue" Content="Blue" GroupName="Color" 
                         HorizontalAlignment="Left"  VerticalAlignment="Top"
                         Click="buttonBlueClick"
                         Margin="5,13,11,3.5" Height="17"/>
            <RadioButton x:Name="buttonRed"  Content="Red"  GroupName="Color" 
                         HorizontalAlignment="Left" VerticalAlignment="Top"
                         Click="buttonRedClick"
                         Margin="5,13,5,3.5" Height="17" />
            <RadioButton x:Name="buttonRandom"  Content="Random"  
                         GroupName="Color" Click="buttonRandomClick"
                         HorizontalAlignment="Left" VerticalAlignment="Top"
                         Margin="5,13,5,3.5" Height="17" />
        </StackPanel>
        <!-- These are the standard OK/Cancel buttons -->
        <Button Grid.Row="4" Grid.Column="0" Name="okButton" 
                Click="okButton_Click" IsDefault="True">OK</Button>
        <Button Grid.Row="4" Grid.Column="1" Name="cancelButton" 
                IsCancel="True">Cancel</Button>
    </Grid>
</Window>

Now we add the code behind for the Dialog.Box. By convention, the code used to handle the interface of the dialog box with the rest of the program is named XXX.xaml.fs, where the associated XAML file is named XXX.xaml.

namespace Spirograph

open System.Windows.Controls

type DialogBox(app: App, model: Model, win: MainWindowXaml) as this =
  inherit DialogBoxXaml()

  let myApp   = app
  let myModel = model
  let myWin   = win
  
  // These are the default parameters for the spirograph, changed by this dialog
  // box
  let mutable myR = 220                 // outer circle radius
  let mutable myr = 65                  // inner circle radius
  let mutable myl = 0.8                 // pen position relative to inner circle
  let mutable myColor = MBlue           // pen color

  // These are the dialog box controls. They are initialized when the dialog box
  // is loaded in the whenLoaded function below.
  let mutable RBox: TextBox = null
  let mutable rBox: TextBox = null
  let mutable lBox: TextBox = null

  let mutable blueButton: RadioButton   = null
  let mutable redButton: RadioButton    = null
  let mutable randomButton: RadioButton = null

  // Call this functions to enable or disable parameter input depending on the
  // state of the randomButton. This is a () -> () function to keep it from
  // being executed before we have loaded the dialog box below and found the
  // values of TextBoxes and RadioButtons.
  let enableParameterFields(b: bool) = 
    RBox.IsEnabled <- b
    rBox.IsEnabled <- b
    lBox.IsEnabled <- b

  let whenLoaded _ =
    // Load and initialize text boxes and radio buttons to the current values in 
    // the model. These are changed only if the OK button is clicked, which is 
    // handled below. Also, if the color is Random, we disable the parameter
    // fields.
    RBox <- this.FindName("radiusR") :?> TextBox
    rBox <- this.FindName("radiusr") :?> TextBox
    lBox <- this.FindName("ratiol")  :?> TextBox

    blueButton   <- this.FindName("buttonBlue")   :?> RadioButton
    redButton    <- this.FindName("buttonRed")    :?> RadioButton
    randomButton <- this.FindName("buttonRandom") :?> RadioButton

    RBox.Text <- myModel.MyR.ToString()
    rBox.Text <- myModel.Myr.ToString()
    lBox.Text <- myModel.Myl.ToString()

    myR <- myModel.MyR
    myr <- myModel.Myr
    myl <- myModel.Myl
  
    blueButton.IsChecked   <- new System.Nullable<bool>(myModel.MyColor = MBlue)
    redButton.IsChecked    <- new System.Nullable<bool>(myModel.MyColor = MRed)
    randomButton.IsChecked <- new System.Nullable<bool>(myModel.MyColor = MRandom)
   
    myColor <- myModel.MyColor
    enableParameterFields(not (myColor = MRandom))

  let whenClosing _ =
    // Show the actual spirograph parameters in a message box at close. Note the 
    // \n in the sprintf gives us a linebreak in the MessageBox. This is mainly
    // for debugging, and it can be deleted.
    let s = sprintf "R = %A\nr = %A\nl = %A\nColor = %A" 
                    myModel.MyR myModel.Myr myModel.Myl myModel.MyColor
    System.Windows.MessageBox.Show(s, "Spirograph") |> ignore
    ()
  
  let whenClosed _ =
    () 
  
  do 
    this.Loaded.Add whenLoaded
    this.Closing.Add whenClosing
    this.Closed.Add whenClosed

  override this.buttonBlueClick(sender: obj, 
                                eArgs: System.Windows.RoutedEventArgs) =
    myColor <- MBlue
    enableParameterFields(true)
    () 
  
  override this.buttonRedClick(sender: obj, 
                               eArgs: System.Windows.RoutedEventArgs) =
    myColor <- MRed      
    enableParameterFields(true)
    () 
  
  override this.buttonRandomClick(sender: obj, 
                                  eArgs: System.Windows.RoutedEventArgs) =
    myColor <- MRandom
    enableParameterFields(false)
    () 
  
  override this.okButton_Click(sender: obj,
                               eArgs: System.Windows.RoutedEventArgs) =
    // Only change the spirograph parameters in the model if we hit OK in the 
    // dialog box.
    if myColor = MRandom
    then myModel.Randomize
    else myR <- RBox.Text |> int
         myr <- rBox.Text |> int
         myl <- lBox.Text |> float

         myModel.MyR   <- myR
         myModel.Myr   <- myr
         myModel.Myl   <- myl
         model.MyColor <- myColor

    // Note that setting the DialogResult to nullable true is essential to get
    // the OK button to work.
    this.DialogResult <- new System.Nullable<bool> true         
    () 

Much of the code here is devoted to ensuring that the spirograph parameters in Spirograph.fs match those shown in this dialog box. Note that there is no error checking: If you enter a floating point for the integers expected in the top two parameter fields, the program will crash. So, please add error checking in your own effort.

Note also that the parameter input fields are disabled with Random color is picked in the radio buttons. It's here just to show how it can be done.

In order to move data back and forth between the dialog box and the program I use the System.Windows.Element.FindName() to find the appropriate control, cast it to the control it should be, and then get the relevant settings from the Control. Most other example programs use data binding. I did not for two reasons: First, I couldn't figure out how to make it work, and second, when it didn't work I got no error message of any kind. Maybe someone who visits this on StackOverflow can tell me how to use data binding without including a whole new set of NuGet packages.

Create the main window in XAML

You have to create a XAML file that defines the main window that contains our menu and drawing space. Here's the XAML code in MainWindow.xaml:

<!-- This defines the main window, with a menu and a canvas. Note that the Height
     and Width are overridden in code to be 2/3 the dimensions of the screen -->
<Window
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    Title="Spirograph" Height="200" Width="300">
    <!-- Define a grid with 3 rows: Title bar, menu bar, and canvas. By default
         there is only one column -->
    <Grid>
        <Grid.RowDefinitions>
            <RowDefinition Height="Auto"/>
            <RowDefinition Height="*"/>
            <RowDefinition Height="Auto"/>
        </Grid.RowDefinitions>
        <!-- Define the menu entries -->
        <Menu  Grid.Row="0">
            <MenuItem Header="File">
                <MenuItem Header="Exit"
                          Name="menuExit"/>
            </MenuItem>
            <MenuItem Header="Spirograph">
                <MenuItem Header="Parameters..."
                          Name="menuParameters"/>
                <MenuItem Header="Draw"
                          Name="menuDraw"/>
            </MenuItem>
            <MenuItem Header="Help">
                <MenuItem Header="About"
                          Name="menuAbout"/>
            </MenuItem>
        </Menu>
        <!-- This is a canvas for drawing on. If you don't specify the coordinates
             for Left and Top you will get NaN for those values -->
        <Canvas Grid.Row="1" Name="myCanvas" Left="0" Top="0">
        </Canvas>
    </Grid>
</Window>

Comments are usually not included in XAML files, which I think is a mistake. I've added some comments to all the XAML files in this project. I don't assert they are the best comments ever written, but they at least show how a comment should be formatted. Note that nested comments are not allowed in XAML.

Set up the Project

We'll assume you're doing this in Visual Studio 2015 (VS 2015 Community, in my case). Create an empty Console project in VS. In Project | Properties change the Output Type to Windows Application.

Next, use NuGet to add FsXaml.Wpf to the project; this package was created by the estimable Reed Copsey, Jr., and it greatly simplifies using WPF from F#. On installation, it will add a number of other WPF assemblies, so you will not have to. There are other similar packages to FsXaml, but one of my goals was to keep the number of tools as small as possible in order to make the overall project as simple and maintaiable as possible.

In addition, add UIAutomationTypes as a reference; it comes as part of .NET.