VB.NET Events Overview

VB.NET Events

• Events are essential for handling user interactions and system notifications in Windows Forms applications.
• Events are triggered by user actions or system states and allow developers to respond accordingly.
• Events are used extensively in VB.NET to create interactive and responsive applications.

Common VB.NET Events

• Click: The most common event, occurs when the user clicks a control, such as a button.
• DoubleClick: Occurs when the user double-clicks on a control.
• MouseEnter: Happens when the mouse pointer enters the boundaries of a control, allowing for actions like highlighting or showing tooltips.
• MouseLeave: Happens when the mouse pointer exits the boundaries of a control, allowing for actions like restoring a control to its default state.
• MouseHover: Activated when the mouse pointer hovers over a control for a specified time period, allowing for actions like showing a popup or displaying additional information.
• KeyPress: Occurs when a key is pressed while the control has focus.
• KeyUp: Occurs when a key is released while the control has focus.
• KeyDown: Occurs when a key is pressed down while the control has focus.
• TextChanged: Happens whenever the text within a control like a TextBox or ComboBox is changed.
• SelectionChanged: Called when an item is selected within a ListBox or ComboBox.
• ValueChanged: Occurs when the value of controls like NumericUpDown, TrackBar, or DateTimePicker is changed.
• CheckedChanged: Used to react when a CheckBox or RadioButton control changes its state.
• ItemClicked (for MenuStrip): Occurs when a menu item is clicked within a MenuStrip.
• LinkClicked (for LinkLabel): Happens when a link embedded in a LinkLabel is clicked.
• FormClosing: Triggered when a form is about to close, providing a chance to perform actions like saving data or confirming the close operation.
• Load: Happens when a form or control is loaded and becomes visible on the screen.
• Resize: Occurs when the size of a form or control is changed.
• Activated: Triggered when a form or control gains focus and becomes the active window.
• Deactivate: Occurs when a form or control loses focus, allowing for actions like saving data or updating states.
• TimerTick: Occurs at regular intervals determined by a Timer control, allowing for actions like updating data periodically or triggering animations.

VB.NET Methods

• Methods, also known as functions or subroutines, provide building blocks for executing specific tasks within your VB.NET programs.
• Methods allow you to encapsulate reusable code and prevent repetition, making your code more organized, efficient, and maintainable.
• While VB.NET has a extensive collection of built-in methods, developers can create their own methods to encapsulate custom functionality and enhance the reusability of their code.

Common VB.NET Methods

String Manipulation Methods

• String.Concat(): Joins several strings together into a single string.

  Dim result As String = String.Concat("Hello", " ", "India")
  

• String.Length: Calculates the number of characters in a string.

  Dim length As Integer = “Hello India".Length
  

• String.Substring(): Extracts a portion of a string, allowing you to work with specific sections of data.

  Dim subString As String = "Hello World".Substring(0, 5)
  ' [Output = Hello]
  

• String.ToUpper() and String.ToLower(): Converts a string to uppercase or lowercase, respectively, allowing for case-sensitive manipulations.

  Dim uc As String = “Hello”.ToUpper()
  ' [Output = HELLO]
  Dim lc As String = "World".ToLower()
  ' [Output = world]
  

Mathematical Methods

• Math.Abs(): Returns the absolute value (+) of a number, providing the distance from zero.

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

• Math.Round(): Rounds a floating-point number to the nearest integer, allowing for precise rounding.

  Dim roundedValue As Integer =  Math.Round(3.7)
  ' [Output = 4]
  

• Math.Max() and Math.Min(): Determines the maximum or minimum of two numbers.

  Dim maxValue As Integer = Math.Max(10, 5)
  ' [Output = 10]
  Dim minValue As Integer = Math.Min(10, 5)
  ' [Output = 5]
  

File and I/O Methods

• System.IO.File.ReadAllText(): Loads the entire contents of a text file into a string.

  Dim text As String = System.IO.File.ReadAllText("file.txt")
  

• System.IO.File.WriteAllText(path, text): Writes a string or contents to a text file.

  System.IO.File.WriteAllText("file.txt”, “Hello, World!")
  

• System.IO.File.Exists(): Verifies whether a file exists at a specific path.

  Dim exists As Boolean = System.IO.File.Exists(“file.txt”)
  

• File.ReadAllLines(path): Reads all lines from a text file into a String array, allowing you to work with each line of the file individually.
• Directory.CreateDirectory(path): Creates a new directory at the specified path.

Date and Time Methods

• DateTime.Now(): Retrieves the current date and time, giving you access to the system's date and time information.
• DateTime.Today(): Gets the current date only, excluding the time component.
• DateTime.AddDays(days): Adds a specific number of days to a date, allowing you to work with time spans and calculate future dates.
• DateTime.Parse(dateString): Converts a string representation of a date into a DateTime object.

Conversion Methods

• Convert.ToInt32(value): Converts a value to an integer.
• Convert.ToDouble(value): Converts a value to a floating-point number of type Double.
• Convert.ToString(value): Converts a value to a string representation.

MessageBox Methods

• MessageBox.Show(message): Displays a simple message box with a message.
• MessageBox.Show(message, caption): Displays a message box with a custom caption.
• MessageBox.Show(message, caption, buttons): Displays a message box with a message, a caption, and a set of buttons allowing the user to interact with the message.

User-Defined Methods

• User-defined methods allow VB.NET developers to encapsulate custom functionality in reusable blocks of code, contributing to modularity and maintainability.
• They can improve code organization and promote code reusability.
• They're defined using the Function and Sub keywords.

Console Input/Output Methods

• Console Input():
  • Console.ReadLine(): Reads a line of input from the console, enabling you to interact with the user.
• Console Output():
  • Console.WriteLine(): Outputs text to the console, allowing your programs to display information to the user.

VB.NET Properties

• Properties act as gateways to private fields within classes, allowing developers to control access to data and maintain encapsulation.
• Properties provide controlled access to data members by defining how data can be retrieved (Get) and modified (Set ).

Common VB.NET Properties

• Get Property (Read-Only Property): Allows reading the value of a private field but prevents direct modification.
• Set Property (Write-Only Property): Allows modifying the value of a private field but prevents reading it directly.
• Read/Write Property: This is the most common property type, and it allows both reading and writing of a private field, providing full control over data access.