TrivialBehinds

A Micro Dependency Injector to make Windows Forms development in F# cheap and fun. Or even in C#.

You may also want to read a related blog post on creating a Windows Forms GUI with F#.

Installation

Available on Nuget: https://www.nuget.org/packages/TrivialBehinds/

Elevator pitch

You want to use the Visual Studio Forms Designer because hand writing the GUI creation code is messy.
You don't want to couple the GUI code with Forms class because the Form class should be mostly autogenerated. Logic, event binding code etc. lives elsewhere.
That elsewhere can be in another project, e.g. in an F# application that obviously needs to be compiled separately.

Use case stories

As an aspiring F# programmer, I have avoided doing Forms stuff because it's only properly supported in C# (with Designer)
As a succesfull but aging C# programmer, I don't want to go down the rabbit hole of the more sophisticated, but boilerplate and abstraction ridden archituctures (Model-View-Presenter, MVVM, ...).

Both of these beautiful dreams can be realized with a tiny library, written expressly for this purpose.

Hybrid F# - C# project

Create solution with two projects: DesignerPart.csproj (a C# Forms application) and FsMain.fsproj (an F# console application).
Draw and test the UI in DesignerPart
Change all the controls listed on Form1.Design.cs to public

Now, TrivialBehinds steps in. In Form1.cs, after InitializeComponent call in ctor, we'll add the only bit of C# code (call to CreateComponentBehind) we need:

public Form1()
{
    InitializeComponent();
    TrivialBehinds.CreateComponentBehind(this);
}

it requests the instantiation of a "behind" class that corresponds to the form class "Form1". This "behind" class will hook up the events and implements all the UI logic in F#. Note that the DesignerPart doesn't need dll or project reference to the "behind" part.

The F# side

Huh, now to wash away that dirty feeling of authoring C# by switching to F# side:

Create "New F# Console application" (there is no Forms option)
Add a project reference to DesignerPart (because you will find both Form1 and Form1Ui class there)
Implement the "Behind" part, which has all the real logic:

type Form1Behind(ui: Form1) =
    let mutable counter = 0

    let showCount() =
        ui.label1.Text <- sprintf "Count is: %d" counter

    do
        ui.btnPlus.Click.Add <|
            fun _ ->
                counter <- counter+1
                showCount()
        ui.btnMinus.Click.Add <|
            fun _ ->
                counter <- counter-1
                showCount()

Modify the 'main' like so:

[<EntryPoint; STAThread>]
let main argv =
    TrivialBehinds.RegisterBehind<Form1, Form1Behind>()
    use form = new Form1()
    Application.Run(form)
    0

That's it! Set the F# side as startup project and press f5 to debug to your heart's content.

If that extra terminal window on launch bothers you, change outputtype form Exe to WinExe in FsMain.fsproj:

<OutputType>WinExe</OutputType>

Extra notes

Windows Forms apps have fuzzy font rendering on Windows 10, unless you do a trick and compile with .NET Framework 4.7. Don't even think about publishing a Windows Forms app without this.