Mahmoud Abas, Full-Stack Software Engineer & AI

Operating Systems 1 (2026-2027) - Windows Forms: Your First Desktop Form

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Operating Systems 1, Lab 1

Windows Forms: Your First Desktop Form

Drag controls onto a form, set their properties, and make them react to events.

Objectives

Explain what a Windows Forms application, a form and a control are
Create a project and find the Form Designer, Toolbox and Properties window
Build Hello World by changing one property of a Label
Add GroupBox, Label, TextBox, ListBox, RadioButton, CheckBox and Button, each with a meaningful Name
Write event handlers for a ListBox and a Button
Fill a TreeView with nodes and show a picture in a PictureBox

Part 1

What a Windows Forms App Is

A form, its controls, and the C# behind them

A Form and Its Controls

Windows Forms application: A program that runs on the desktop computer and shows one or more windows, called forms.

Control: Something placed on a form: a label, a text box, a list box, a button, and many more.

Three Roles on a Login Screen

A login form with User Name and Password labels, two text boxes and a Login button

Labels describe the controls next to them
Text boxes hold what the user types: user name and password
The button has code attached: clicking Login runs it, for example to check the password

Everything on the Form Is a C# Object

In the designer	In C#
Your form, `Form1`	A class that inherits from `Form`, which already draws the title bar and the buttons
Drag a control onto the form	A new field of that control's class, and a new object in it
Change a value in Properties	Set a property of that object, for example `Text`
Double-click a control	A new method that runs when one of its events happens

Part 2

Hello World

A new project, one label, one property

Create the Project

Launch Visual Studio and choose New, Project
Choose Windows Forms Application (recent versions: Windows Forms App, under the Desktop filter)
Name it DemoApplication and choose a location
Click OK (or Create)

What Visual Studio Opens

Window	What it is for
Form Designer	The design surface where you build the form
Solution Explorer	The project files: `Form1.cs` and `Program.cs`
Toolbox	Every control you can add: Label, TextBox, Button, ...
Properties window	The properties of the selected control

Two Code Files

Program.cs starts the application; Form1.cs holds the code of the form

csharp

static void Main()
{
    ApplicationConfiguration.Initialize();
    Application.Run(new Form1());
}

Program.cs

Application.Run(new Form1()) creates the first form and shows it
Closing that main form ends the application
Form1 is a partial class: Form1.cs for your code, Form1.Designer.cs for the designer's code

Add a Label, Set Its Text

From the Toolbox, drag a Label onto the form
Right-click the label and choose Properties
In the Properties window, set Text to Hello World
Press Start to run the program

Predict: What Does the Designer Write?

You dragged a Label and typed Hello World into Text. Which lines appear in Form1.Designer.cs?

csharp

this.label1 = new System.Windows.Forms.Label();
this.label1.AutoSize = true;
this.label1.Location = new System.Drawing.Point(150, 110);
this.label1.Name = "label1";
this.label1.TabIndex = 0;
this.label1.Text = "Hello World";
this.Controls.Add(this.label1);
private System.Windows.Forms.Label label1;

Our Form1.Designer.cs: a new object, one line per property, Controls.Add, a field. VS 2022 on .NET 8 writes it shorter (label1 = new Label();, no this.) and adds a label1.Size line.

Run It

Part 3

The User Details Form

Seven kinds of controls on one form

The Target Form

Enter a name and an address, choose a city, a gender, and the courses to learn

The finished User Details form running on Windows

GroupBox and Label

GroupBox: Groups controls into a section. The name and the address are details of one person, so they sit together.

Label: Displays a text to the user, normally to say what to fill in next to another control.

TextBox and the Name Property

TextBox: Lets the user enter text on the form.

Drag two TextBoxes: one for the name, one for the address
Set their Name property to txtName and txtAddress
The Name is the variable you use for the control in your code

The Naming Convention

Control	Prefix	Example
TextBox	`txt`	txtName, txtAddress
ListBox	`lst`	lstCity
RadioButton	`rd`	rdMale, rdFemale
CheckBox	`chk`	chkC, chkASP
Button	`btn`	btnSubmit

ListBox: The String Collection Editor

Drag a ListBox; set its Name to lstCity
Click the Items property: (Collection)
Type one city per line: Mumbai, Bangalore, Hyderabad
Click OK

csharp

this.lstCity.Items.AddRange(new object[] {
"Mumbai",
"Bangalore",
"Hyderabad"});

What the editor writes

Predict: RadioButton or CheckBox?

Gender: one answer. Courses: C#, ASP.Net, or both. Which control fits each?

Control	The user chooses	Our controls
RadioButton	exactly one option	rdMale, rdFemale
CheckBox	several options	chkC, chkASP

The Remaining Controls

The Submit button will read everything the user entered

Control	Text	Name
RadioButton	Male	rdMale
RadioButton	Female	rdFemale
CheckBox	C#	chkC
CheckBox	ASP.Net	chkASP
Button	Submit	btnSubmit

Try It: Build a Form, Watch the Code

Part 4

Events

Code that runs when something happens

Events and Event Handlers

Event: Something that happens when an action is performed. The most common one: clicking a button.

Event handler: A method that runs when its event happens, for example the code that processes the form.

Double-Click Creates the Handler

Double-click the ListBox in the Form Designer. The method then runs whenever an item is selected.

csharp

// Form1.cs: an empty method
private void lstCity_SelectedIndexChanged(object sender, EventArgs e)
{

}
// Form1.Designer.cs: one line that wires it to the event
this.lstCity.SelectedIndexChanged +=
    new System.EventHandler(this.lstCity_SelectedIndexChanged);

Every Control Has a Default Event

Double-click creates the handler for this one. Read from Windows Forms by a program we ran.

Control	Default event
Button, Label	`Click`
TextBox	`TextChanged`
ListBox	`SelectedIndexChanged`
CheckBox, RadioButton	`CheckedChanged`
The form itself	`Load`

Worked Example: Show the Selected City

csharp

private void lstCity_SelectedIndexChanged(object sender, EventArgs e)
{
    string text = lstCity.GetItemText(lstCity.SelectedItem);
    MessageBox.Show(text);
}

lstCity.SelectedItem: the item the user selected
GetItemText gets its text, stored in text
MessageBox.Show displays it

Predict: The User Clicks Bangalore

What appears on the screen?

Bangalore is selected in the list and a message box shows Bangalore

Worked Example: The Submit Button

Double-click the button, then add three lines

csharp

private void btnSubmit_Click(object sender, EventArgs e)
{
    string name = txtName.Text;
    string address = txtAddress.Text;
    MessageBox.Show(name + address);
}

What the user typed is in each text box's Text property
Copy the two values into name and address
Show them in a message box

Predict: The Submit Message

The user types Student and Mansoura, then clicks Submit. What exactly does the box say?

Predict: A Name That Does Not Match

The Name property says txtUser, but the handler still reads txtName.Text. What happens?

text

Form1.cs(21,27): error CS0103: The name 'txtName' does not exist in the current context

The real compiler message (file path shortened)

Part 5

TreeView and PictureBox

A tree of nodes and a picture

TreeView: The TreeNode Editor

Lists items like a tree, as Windows Explorer shows folders

Click the Nodes property: the TreeNode Editor opens
Add Root, set its Text to Root
Add Child three times: Label, Button, Checkbox
Click OK

Root

Label

Button

Checkbox

Predict: How Does the Designer Store the Tree?

Four nodes. Which objects are created, and in what order?

csharp

TreeNode treeNode1 = new TreeNode("Label");
TreeNode treeNode2 = new TreeNode("Button");
TreeNode treeNode3 = new TreeNode("Checkbox");
TreeNode treeNode4 = new TreeNode("Root",
    new TreeNode[] { treeNode1, treeNode2, treeNode3 });
this.treeView1.Nodes.AddRange(new TreeNode[] { treeNode4 });

Shortened from our Form1.Designer.cs

PictureBox: The Image Property

Drag a PictureBox onto the form
Click its Image property: a window pops up
Click Import and choose the image
Click OK

The Finished Form

Student and Mansoura typed, Male and C# selected

Quick Check

Exactly one faculty level out of four: RadioButton or CheckBox?
Which property holds what the user typed in a TextBox?
Which property is the control's name in your code?
How do you get a Click handler for a button?
Which method runs when the user selects Hyderabad?

Part 6

Practice

About 30 minutes: build it, run it, compare

About 10 minutes

Practice 1: The Login Form

Control	Text	Name
Label	User Name	label1
Label	Password	label2
TextBox	(empty)	txtUser, txtPassword
Button	Login	btnLogin

Practice 1: Answer

csharp

private void btnLogin_Click(object sender, EventArgs e)
{
    string user = txtUser.Text;
    MessageBox.Show("Welcome " + user);
}

The login form with admin typed and a message box that says Welcome admin

About 4 minutes

Practice 2: Predict the Message

Each handler reads name and address from the text boxes. The user types Student and Cairo: write the exact message of each button.

csharp

// button A
MessageBox.Show(name + " " + address);
// button B
MessageBox.Show("Name: " + name);
// button C
MessageBox.Show(address + name);

Practice 2: Answer

Button	Message on screen
A	`Student Cairo`
B	`Name: Student`
C	`CairoStudent`

About 8 minutes

Practice 3: A List of Courses

Form Text Courses, a Label Choose a course
ListBox lstCourse: C#, ASP.Net, Operating Systems
Button btnShow, Text Show: shows You chose + the selected course

The Courses form: a label, a list of three courses and a Show button

Practice 3: Answer

csharp

private void btnShow_Click(object sender, EventArgs e)
{
    string course = lstCourse.GetItemText(lstCourse.SelectedItem);
    MessageBox.Show("You chose " + course);
}

Operating Systems selected; the message box says You chose Operating Systems

About 4 minutes

Practice 4: Find the Bug

The ListBox is named lstCourse. Will this run?

csharp

private void btnShow_Click(object sender, EventArgs e)
{
    string course = lstCourses.GetItemText(lstCourses.SelectedItem);
    MessageBox.Show("You chose " + course);
}

Practice 4: Answer

text

Form1.cs(12,29): error CS0103: The name 'lstCourses' does not exist in the current context
Form1.cs(12,52): error CS0103: The name 'lstCourses' does not exist in the current context

The real compiler output (file path shortened)

About 4 minutes

Practice 5: Choose the Controls

A student registration form: pick a control and a Name for each

The student's full name
The faculty level: exactly one of four
The hobbies: any number of four
The city, from a list
A button that saves the form

Practice 5: Answer

Information	Control	Name
Full name	TextBox	txtName
Faculty level	4 RadioButtons	rdLevel1 to rdLevel4
Hobbies	4 CheckBoxes	chkReading, chkSport, ...
City	ListBox	lstCity
Save	Button	btnSave

Key Takeaways

A form is a class; every control on it is an object with properties
The designer writes the C# for you in Form1.Designer.cs
Give controls meaningful Names: the Name is the variable in your code
RadioButton for one choice, CheckBox for several
Double-click a control to get the handler for its default event

Open this lesson

Mahmoud AbasWindows Forms: Your First Desktop Form

In the designer

In C#

Your form, Form1

A class that inherits from Form, which already draws the title bar and the buttons

Drag a control onto the form

A new field of that control's class, and a new object in it

Change a value in Properties

Set a property of that object, for example Text

Double-click a control

A new method that runs when one of its events happens

Window

What it is for

Form Designer

The design surface where you build the form

Solution Explorer

The project files: Form1.cs and Program.cs

Toolbox

Every control you can add: Label, TextBox, Button, ...

Properties window

The properties of the selected control

this.label1 = new System.Windows.Forms.Label(); this.label1.AutoSize = true; this.label1.Location = new System.Drawing.Point(150, 110); this.label1.Name = "label1"; this.label1.TabIndex = 0; this.label1.Text = "Hello World"; this.Controls.Add(this.label1); private System.Windows.Forms.Label label1;

Control

Prefix

Example

TextBox

txt

txtName, txtAddress

ListBox

lst

lstCity

RadioButton

rd

rdMale, rdFemale

CheckBox

chk

chkC, chkASP

Button

btn

btnSubmit

Control

The user chooses

Our controls

RadioButton

exactly one option

rdMale, rdFemale

CheckBox

several options

chkC, chkASP

Control

Text

Name

RadioButton

Male

rdMale

RadioButton

Female

rdFemale

CheckBox

chkC

CheckBox

ASP.Net

chkASP

Button

Submit

btnSubmit

// Form1.cs: an empty method private void lstCity_SelectedIndexChanged(object sender, EventArgs e) { } // Form1.Designer.cs: one line that wires it to the event this.lstCity.SelectedIndexChanged += new System.EventHandler(this.lstCity_SelectedIndexChanged);

Control

Default event

Button, Label

Click

TextBox

TextChanged

ListBox

SelectedIndexChanged

CheckBox, RadioButton

CheckedChanged

The form itself

Load

TreeNode treeNode1 = new TreeNode("Label"); TreeNode treeNode2 = new TreeNode("Button"); TreeNode treeNode3 = new TreeNode("Checkbox"); TreeNode treeNode4 = new TreeNode("Root", new TreeNode[] { treeNode1, treeNode2, treeNode3 }); this.treeView1.Nodes.AddRange(new TreeNode[] { treeNode4 });

Control

Text

Name

Label

User Name

label1

Label

Password

label2

TextBox

(empty)

txtUser, txtPassword

Button

btnLogin

Button

Message on screen

Student Cairo

Name: Student

CairoStudent

Information

Control

Name

Full name

TextBox

txtName

Faculty level

4 RadioButtons

rdLevel1 to rdLevel4

Hobbies

4 CheckBoxes

chkReading, chkSport, ...

City

ListBox

lstCity

Save

Button

btnSave