Overview of Using Controls in Windows Forms

This topic describes the essential elements of a Windows Forms application and provides a simple example that uses controls and handles events in a Windows Forms application.

Simple Windows Forms Applications

At a minimum, a Windows Forms application consists of the following elements:

• One or more classes that derive from System.Windows.Forms.Form.
• A Main method that invokes the static (shared) System.Windows.Forms.Application.Run method and passes a Form instance to it. The Application.Run method processes messages from the operating system to the application.

The following code example shows the essential elements of a Windows Forms application.

Option Explicit
Option Strict

Imports System
Imports System.Windows.Forms

Public Class MyForm
   Inherits Form
   
   Public Sub New()
      Me.Text = "Hello World"
   End Sub 'New
   
   <STAThread()> _
   Public Shared Sub Main()
      Dim aform As New MyForm()
      ' The Application.Run method processes messages from the operating system 
      ' to your application. If you comment out the next line of code, 
      ' your application will compile and execute, but because it is not in the
      ' message loop, it will exit after an instance of the form is created.
      Application.Run(aform)
   End Sub
End Class
[C#]
using System;
using System.Windows.Forms;

public class MyForm : Form {

   public MyForm() {
      this.Text = "Hello World";
   }
   [STAThread]
   public static void Main(string[] args) {
     MyForm aform = new MyForm();
// The Application.Run method processes messages from the operating system 
// to your application. If you comment out the next line of code, 
// your application will compile and execute, but because it is not in the // message loop, it will exit after an instance of the form is created.
      Application.Run(aform);
   }
}

Using Controls in a Windows Forms Application

The following code example shows a simple application that illustrates how Windows Forms applications use controls and handle events. The example consists of three buttons on a form; each button changes the background color when clicked.

Option Explicit
Option Strict

Imports System
Imports System.ComponentModel
Imports System.Windows.Forms
Imports System.Resources
Imports System.Drawing

Public Class MyForm
   Inherits Form
   Private red As Button
   Private blue As Button
   Private green As Button
   
   Public Sub New()
      InitializeComponent()
   End Sub
   
   
   Protected Overloads Overrides Sub Dispose(disposing as Boolean)
      MyBase.Dispose(disposing)
   End Sub
   
   ' InitializeComponent is a helper method for the constructor. 
   ' It is included for consistency with code that is 
   ' auto-generated by the Windows Forms designer in Visual Studio .NET. 
   Private Sub InitializeComponent()
      
      ' Creates three buttons, sets their properties, and attaches
      ' an event handler to each button.
      red = New Button()
      red.Text = "Red"
      red.Location = New Point(100, 50)
      red.Size = New Size(50, 50)
      AddHandler red.Click, AddressOf button_Click
      Controls.Add(red)
      
      blue = New Button()
      blue.Text = "Blue"
      blue.Location = New Point(100, 100)
      blue.Size = New Size(50, 50)
      AddHandler blue.Click, AddressOf button_Click
      Controls.Add(blue)
      
      green = New Button()
      green.Text = "Green"
      green.Location = New Point(100, 150)
      green.Size = New Size(50, 50)
      AddHandler green.Click, AddressOf button_Click
      Controls.Add(green)
   End Sub
   
   ' Event handler.
   Private Sub button_Click(sender As Object, e As EventArgs)
      If sender Is red Then
         Me.BackColor = Color.Red
      Else
         If sender Is blue Then
            Me.BackColor = Color.Blue
         Else
            Me.BackColor = Color.Green
         End If
      End If 
   End Sub

   ' The STAThreadAttribute informs the common language runtime that
   ' Windows Forms uses the single-threaded apartment model.
   <STAThread()> _
   Public Shared Sub Main()
      Application.Run(New MyForm())
   End Sub
End Class
[C#]
using System;
using System.ComponentModel;
using System.Windows.Forms;
using System.Resources;
using System.Drawing;

public class MyForm : Form {
   private Button red;
   private Button blue;
   private Button green;

   public MyForm() : base() {   
      InitializeComponent();   
   }

   protected override void Dispose(bool disposing) {
      base.Dispose(disposing);
   }
   
// InitializeComponent is a helper method for the constructor. 
// It is included for consistency with code that is 
// auto-generated by the Windows Forms designer in Visual Studio .NET. 
   private void InitializeComponent() {
   
// A delegate for the click event of a button. The argument to 
// the constructor contains a reference to the method that performs the 
// event handling logic.
      EventHandler handler = new EventHandler(button_Click);
   
// Creates three buttons, sets their properties, and attaches
// an event handler to each button.

      red = new Button();
      red.Text = "Red";
      red.Location = new Point(100, 50);
      red.Size = new Size(50, 50);
      red.Click +=handler;
      Controls.Add(red);
      
      blue = new Button();
      blue.Text = "Blue";
      blue.Location = new Point(100, 100);
      blue.Size = new Size(50, 50);
      blue.Click += handler;
      Controls.Add(blue);
      
      green = new Button();
      green.Text = "Green";
      green.Location = new Point(100, 150);
      green.Size = new Size(50, 50);
      green.Click += handler;
      Controls.Add(green);      
      }
      
   // Event handler.
   private void button_Click(object sender, EventArgs e) {
            if (sender == red) this.BackColor = Color.Red ;
                  else if (sender == blue) this.BackColor = Color.Blue;
                  else this.BackColor = Color.Green;
        }
   // The STAThreadAttribute informs the common language runtime that
   // Windows Forms uses the single-threaded apartment model.
  [STAThread]
   public static void Main(string[] args) {
   Application.Run(new MyForm());
   }
   
}

See Also

Windows Forms Component Hierarchy | Windows Forms Control Development Basics