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Widgets in GTK#

last modified October 18, 2023

In this part of the GTK# programming tutorial, we introduce some GTK# widgets.

Widgets are basic building blocks of a GUI application. Over the years, several widgets became a standard in all toolkits on all OS platforms. For example a button, a check box or a scroll bar. The GTK# toolkit’s philosophy is to keep the number of widgets at a minimum level. More specialised widgets are created as custom GTK# widgets.

Label

The Label widget shows text.

label.cs

using Gtk;

class SharpApp : Window {

string text = @“Meet you downstairs in the bar and heard your rolled up sleeves and your skull t-shirt You say why did you do it with him today? and sniff me out like I was Tanqueray

cause you’re my fella, my guy hand me your stella and fly by the time I’m out the door you tear men down like Roger Moore

I cheated myself like I knew I would I told ya, I was trouble you know that I’m no good”;

public SharpApp() : base("You know I'm No Good")
{
    BorderWidth = 8;
    SetPosition(WindowPosition.Center);
    
    DeleteEvent += delegate { Application.Quit(); };

    Label lyrics = new Label(text);
    Add(lyrics);
    
    ShowAll();
}

public static void Main()
{
    Application.Init();
    new SharpApp();
    Application.Run();
}

}

The code example shows some lyrics on the window.

string text = @"Meet you downstairs in the bar and heard

your rolled up sleeves and your skull t-shirt …

In C# programming language, multiline string is preceded with the @ character.

BorderWidth = 8;

The Label is surrounded by some empty space.

Label lyrics = new Label(text); Add(lyrics);

The Label widget is created and added to the window.

Figure: Label Widget

CheckButton

CheckButton is a widget that has two states: on and off. The On state is visualised by a check mark. It is used to denote some boolean property.

checkbutton.cs

using Gtk; using System;

class SharpApp : Window {

public SharpApp() : base("CheckButton")
{
    SetDefaultSize(250, 200);
    SetPosition(WindowPosition.Center);
    
    DeleteEvent += delegate { Application.Quit(); };
    
    CheckButton cb = new CheckButton("Show title");
    cb.Active = true;
    cb.Toggled += OnToggle;

    Fixed fix = new Fixed();
    fix.Put(cb, 50, 50);

    Add(fix);
    ShowAll();
}

void OnToggle(object sender, EventArgs args) 
{
    CheckButton cb = (CheckButton) sender;

    if (cb.Active) {
        Title = "CheckButton";
    } else {
        Title = " ";
    }
}

public static void Main()
{
    Application.Init();
    new SharpApp();
    Application.Run();
}

}

We display a title in the titlebar of the window, depending on the state of the CheckButton.

CheckButton cb = new CheckButton(“Show title”);

CheckButton widget is created.

cb.Active = true;

The title is visible by default, so we check the check button by default.

CheckButton cb = (CheckButton) sender;

Here we cast the sender object to CheckButton class.

if (cb.Active) { Title = “CheckButton”; } else { Title = " “; }

Depending on the Active property of the CheckButton, we show or hide the title of the window.

Figure: CheckButton

ComboBox

ComboBox is a widget that allows the user to choose from a list of options.

combobox.cs

using Gtk; using System;

class SharpApp : Window {

Label label;

public SharpApp() : base("ComboBox")
{
   string[] distros = new string[] {"Ubuntu",
        "Mandriva",
        "Red Hat",
        "Fedora",
        "Gentoo" };

    SetDefaultSize(250, 200);
    SetPosition(WindowPosition.Center);
    BorderWidth = 7;
    DeleteEvent += delegate { Application.Quit(); };
    
    Fixed fix = new Fixed();

    ComboBox cb = new ComboBox(distros);
    cb.Changed += OnChanged;
    label = new Label("-");
    
    fix.Put(cb, 50, 30);
    fix.Put(label, 50, 140);
    Add(fix);

    ShowAll();
}

void OnChanged(object sender, EventArgs args)
{
    ComboBox cb = (ComboBox) sender;
    label.Text = cb.ActiveText;
}

public static void Main()
{
    Application.Init();
    new SharpApp();
    Application.Run();
}

}

The example shows a combo box and a label. The combo box has a list of six options. These are the names of Linux distros. The label widget shows the selected option from the combo box.

string[] distros = new string[] {“Ubuntu”, “Mandriva”, “Red Hat”, “Fedora”, “Gentoo” };

This is an array of strings that will be shown in the ComboBox widget.

ComboBox cb = new ComboBox(distros);

The ComboBox widget is created. The constructor takes the array of strings as a parameter.

void OnChanged(object sender, EventArgs args) { ComboBox cb = (ComboBox) sender; label.Text = cb.ActiveText; }

Inside the OnChanged method, we get the selected text out of the combo box and set it to the label.

Figure: ComboBox

Image

The next example introduces the Image widget. This widget displays pictures.

image.cs

using Gtk; using System;

class SharpApp : Window {

Gdk.Pixbuf castle;

public SharpApp() : base("Red Rock")
{
    BorderWidth = 1;
    SetPosition(WindowPosition.Center);
    DeleteEvent += delegate { Application.Quit(); };

    try {
        castle = new Gdk.Pixbuf("redrock.png");
    } catch {
        Console.WriteLine("Image not found");
        Environment.Exit(1);
    }

    Image image = new Image(castle);
    Add(image);
    
    ShowAll();
}

public static void Main()
{
    Application.Init();
    new SharpApp();
    Application.Run();
}

}

We show the Red Rock castle in the window.

try { castle = new Gdk.Pixbuf(“redrock.png”); } catch { Console.WriteLine(“Image not found”); Environment.Exit(1); }

We create the Gdk.Pixbuf widget. We put the constructor between the try and catch keywords to handle possible errors.

Image image = new Image(castle); Add(image);

Image widget is created and added to the window.

Figure: Image

In this chapter, we showed the first pack of basic widgets of the GTK# programming library.

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