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GTK# : Widgets in GTK#

Tutorial by:      Date: 2016-04-19 01:32:30

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In this part of the GTK# programming tutorial, we will 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.

Label Widget
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 will 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.

CheckButton
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.

ComboBox
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.

Image
Figure: Image

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

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GTK#

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