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.
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.
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) |> ignoreSpirograph.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.
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="https://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="https://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.
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="https://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="https://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.
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 menuAboutHandlerThere’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.
Add the App.xaml and App.xaml.fs to tie everything together
<!-- All boilerplate for now -->
<Application
xmlns="https://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="https://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.