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Kashif Soofi
Kashif Soofi

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Choose Font with GTK4 and .NET 8

GTK and .NET

GTK is a free and open-source cross-platform widget toolkit for creating graphical user interfaces (GUIs).

.NET is the free, open-source, cross-platform framework for building modern apps and powerful cloud services.

Focus of this tutorial is to write an app to choose font with GTK 4 and C# targeting .NET 8.

Project Setup

Let's begin by installing all necessary tools. First, follow the instructions on the GTK website in order to install GTK 4. Then install .NET by following instructions for your platform from download page. We are targeting GTK4, .NET 8 and Gir.Core.Gtk-4.0 0.5.0-preview.4.

Now lets create a new empty folder named gtk4-dotnet8-fontdialog and execute following to create an empty solution:

dotnet new sln
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Next we will add a console application and add that to our solution

dotnet new console -o FontDialog.App
dotnet sln add FontDialog.App/FontDialog.App.csproj
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New lets add C# bindings for Gtk4 to our Counter.App project

cd Counter.App
dotnet add package GirCore.Gtk-4.0 --version 0.5.0-preview.4
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Now we can run our application by executing:

dotnet run
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At this moment it would print Hello, world!.


Lets start by creating GTK Application and add an OnActivate event handler to create the application window and display it.

GTK provides a widget FontDialogButton to get the selected font. This widget expects a FontDialog to make the font selection, we will create a FontDialog, also available with GTK and then create an instance of FontDialogButton and add it to our window. We don't have to do anything else, clicking on button opens the dialog and selected font is updated on the button.

Code for the program is below following the screenshots.

var application = Gtk.Application.New("org.GirCore.GTK4FontDialog", Gio.ApplicationFlags.FlagsNone);
application.OnActivate += (sender, args) =>
    var fontDialog = Gtk.FontDialog.New();
    var fontDialogButton = Gtk.FontDialogButton.New(fontDialog);

    var gtkBox = Gtk.Box.New(Gtk.Orientation.Vertical, 0);

    var window = Gtk.ApplicationWindow.New((Gtk.Application)sender);
    window.Title = "GTK Choose Font";
    window.SetDefaultSize(300, 300);
    window.Child = gtkBox;
return application.RunWithSynchronizationContext(null);
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Font Dialog Button

Font Dialog

Choose Font with Button

By using FontDialogButton we don't have to manage opening up FontDialog. However if you don't want to use the FontDialogButton then you would need to display FontDialog manually.
Lets add a label to dispaly selected font and a button that we would use to display FontDialog on click.

    var currentFont = fontDialogButton.GetFontDesc();
    var labelFont = Gtk.Label.New(currentFont?.ToString());

    var buttonSelectFont = Gtk.Button.New();
    buttonSelectFont.Label = "Select Font";
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We will setup the click signal handler after creating the window, just before call to Show function. This is required to set the parent of FontDialog. In the handler we will create FontDialog and call ChooseFontAsync function to get the selected font. We are also handling an exception as when user clicks on Cancel button, it results in recoverable GTK error that translates to C# exception.

And add labelCounter as child of window.

    buttonSelectFont.OnClicked += async (_, _) =>
            var fontDialog = Gtk.FontDialog.New();
            var selectedFont = await fontDialog.ChooseFontAsync(window, null);
            labelFont.SetLabel(selectedFont?.ToString() ?? string.Empty);
        catch (Exception ex)
            //Prints "Dismissed by user" if dialog is cancelled

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Running the application now would display window with 2 buttons.

Select Font Button

And selecting the font would update the font label text.

Selected Font


Source code for the demo application is hosted on GitHub in blog-code-samples repository.


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