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.

Explore the key events in VB.NET that facilitate user interaction and enhance application responsiveness. This quiz covers common events like Click, DoubleClick, and Mouse movements, essential for developing dynamic Windows Forms applications.