Events Methods and Properties

Common VB .Net Events

• In Visual Basic .NET (VB.NET), common events refer to the events that are frequently used to respond to user interactions and system notifications in Windows Forms applications.
• These events are associated with various common controls and are used to trigger specific actions or behaviors.
• These events are used and coded as per the requirement of the user’s application.
• Some of the common events in VB.NET are as follows:-

1. Click:

   • Occurs when the user clicks a control, such as a button or a PictureBox.

2. DoubleClick:

   • Occurs when the user double-clicks a control.

3. MouseEnter:

   • Occurs when the mouse pointer enters the boundaries of a control.

4. MouseLeave:

   • Occurs when the mouse pointer exits the boundaries of a control.

5. MouseHover:

   • Occurs when the mouse pointer hovers over a control for a specified duration without moving.

6. MouseClick:

   • Occurs when the user clicks a control using the mouse.

7. MouseDoubleClick:

   • Occurs when the user double-clicks a control using the mouse.

8. KeyPress:

   • Occurs when a key is pressed while the control has focus.

9. KeyUp:

   • Occurs when a key is released while the control has focus.

10. KeyDown:

    • Occurs when a key is pressed down while the control has focus.

11. TextChanged:

    • Occurs when the text within a TextBox or ComboBox control is changed.

12. SelectionChanged:

    • Occurs when the selected item in a ListBox or ComboBox changes.

13. ValueChanged:

    • Commonly used with controls like NumericUpDown, TrackBar, and DateTimePicker to respond to changes in their values.

14. CheckedChanged:

    • Occurs when the state of a CheckBox or RadioButton control changes.

15. ItemClicked (for MenuStrip):

    • Occurs when a menu item is clicked in a MenuStrip control.

16. LinkClicked (for LinkLabel):

    • Occurs when a link is clicked in a LinkLabel control.

17. FormClosing:

    • Occurs when a form is about to close, allowing us to handle closing operations.

18. Load:

    • Occurs when a form or control is loaded and becomes visible.

19. Resize:

    • Occurs when the size of a form or control is changed.

20. Activated:

    • Occurs when a form or control becomes the active window.

21. Deactivate:

    • Occurs when a form or control loses focus.
22. Timer Tick:
    
    • Occurs at regular intervals when a Timer control is enabled.

Common VB .Net Methods

• Visual Basic .NET (VB.NET) is a versatile programming language that offers a wide range of in-built methods and functions for various tasks.
• VB.NET provides a rich set of in-built methods and functions for various tasks, and we can also create our own custom methods to encapsulate reusable functionality in our applications as per requirements.
• Some common in-built methods in VB.NET can be categorized into several areas, which are as follows:-

(A) String Manipulation Methods:

1. String.Concat():

   • This method concatenates two or more strings into a single string.
   • For example – Dim result As String = String.Concat(“Hello”, ” “, “India”)
2. String.Length:
   
   • This method returns the length (number of characters) present in a string.
   • For example – Dim length As Integer = “Hello India”.Length
3. String.Substring():
   
   • This method extracts a portion of a string.
   • For example – Dim subString As String = “Hello World”.Substring(0, 5) [Output = Hello]
4. String.ToUpper() and String.ToLower():
   
   • This method converts a string to uppercase or lowercase respectively.
   • For example – (i) Dim uc As String = “Hello”.ToUpper() [Output = HELLO]
   • (ii) Dim lc As String = “World”.ToLower()     [Output = world]

(B.) Mathematical Methods:

1. Math.Abs():

   • This method returns the absolute value(+) of a number.

     For example - Dim AV As Double = Math.Abs(-5.5) [Output = 5.5]

2. Math.Round():

   • This method rounds a floating-point number to the nearest integer.
   • For example – Dim roundedValue As Integer = Math.Round(3.7) [Output = 4]

3. Math.Max() and Math.Min():

   • This method returns the maximum or minimum of two numbers.
   • For example – (i)Dim maxValue As Integer = Math.Max(10, 5) [Output = 10]
   • (ii)Dim minValue As Integer = Math.Min(10, 5) [Output = 5] 

(C) File and I/O Methods:

1. System.IO.File.ReadAllText():
   
   • This method reads the contents of a text file into a string.
   • For example – Dim text As String = System.IO.File.ReadAllText(“file.txt”)
2. System.IO.File.WriteAllText(path, text):
   
   • Writes a string or contents to a text file, overwriting its contents.
   • For example – System.IO.File.WriteAllText(“file.txt”, “Hello, World!”)

3. System.IO.File.Exists():

   • This method checks if a file exists or not at the specified path.
   • Syntax: File.Exists(path)
   • For example – Dim exists As Boolean = System.IO.File.Exists(“file.txt”)

4. File.ReadAllLines(path):

   • Reads all lines from a text file into an array.

5. Directory.CreateDirectory(path):
   
   • Creates a directory at the specified path.

(D) Date and Time Methods:

• DateTime.Now(): Gets the current date and time.
• DateTime.Today(): Gets the current date without the time.
• DateTime.AddDays(days): Adds days to a date.
• DateTime.Parse(dateString): Parses a string into a DateTime object.

(E) Conversion Methods:

• Convert.ToInt32(value): Converts a value to an integer.
• Convert.ToDouble(value): Converts a value to a double.
• Convert.ToString(value): Converts a value to a string.

(F) MessageBox Methods:

• MessageBox.Show(message): Displays a message box with a message.
• MessageBox.Show(message, caption): Displays a message box with a message and caption.
• MessageBox.Show(message, caption, buttons): Displays a message box with specified buttons.

(G) User-Defined Methods:

• We can create our own methods in VB.NET to perform custom operations.
• These methods are defined using the Function or Sub keyword.

(H) Console Input/Output Methods:

• Console Input():
  • Console.ReadLine() – Used to read user input from the console.
  • For Example - Dim userInput As String = Console.ReadLine()
• Console Output():
  • Console.WriteLine() – Used to display text on the console.
  • For example - Console.WriteLine("Hello, World!")

Common VB .Net Properties

• In Visual Basic .NET (VB.NET), properties are special member variables that provide controlled access to an object’s data.
• Properties allow us to get and set the values of private fields while encapsulating the internal details of the class.
• There are some common types of properties in VB.NET. Properties are essential for encapsulating data and providing controlled access to class members, promoting good object-oriented programming practices and data encapsulation.
• Some common VB.NET properties are:-

  1. Get Property (Read-Only Property):

  • A get-only property allows us to retrieve the value of a private field but doesn’t allow us to modify it.
  • For Example:-

Public ReadOnly Property FirstName As String
     Get
           Return first_name
     End Get
End Property

2. Set Property (Write-Only Property):

• • A set-only property allows us to set the value of a private field but doesn’t allow us to retrieve it.
  • For Example:

Public WriteOnly Property Age As Integer
     Set(value As Integer)
          age = value
     End Set
End Property

3. Get-Set Property (Read-Write Property):

• • A get-set property allows both getting and setting the value of a private field.
  • For Example:

Public Property LastName As String
     Get
          Return last_name
     End Get

     Set(value As String)
          Last_Name = value
     End Set
End Property

• Auto-Implemented Property:

  • An auto-implemented property is a shorthand syntax for creating properties when we don’t need additional logic in the getter or setter. The compiler generates the private field for us.
  • For Example:

Public Property Str As String

• Read-Only Auto-Implemented Property:

  • This property is similar to an auto-implemented property, but it’s read-only.
  • For Example:

Public ReadOnly Property Str As String

• Set-Only Auto-Implemented Property:

  • This property is similar to an auto-implemented property, but it’s write-only.
  • For Example:

Public WriteOnly Property IsEnabled As Boolean

• Indexed Property:

  • An indexed property allows us to access elements of an object as if it were an array.
  • For Example:

Public Property Items(index As Integer) As String
     Get
          Return items(index)
     End Get

     Set(value As String)
          items(index) = value
     End Set
End Property

• Default Property:

  • A default property allows us to access an object using an index or key without specifying the property name.
  • Example:

Default Public Property Item(index As Integer) As String
     Get
          Return items(index)
     End Get

     Set(value As String)
          items(index) = value
     End Set
End Property

• Shared Property (Shared Member):

  • A shared property is associated with the class itself rather than with instances of the class.
  • It’s accessed using the class name.
  • For Example:

Public Shared Property CompanyName As String

• Custom Properties:

  • We can create our own custom properties with additional logic in the getter or setter to perform validation, calculations, or other operations as needed.