Visual Basic .NET Core Patterns Modern VB.NET (2019+) best practices with focus on type safety, LINQ, async/await, and .NET integration. Quick Start ' Always enable strict type checking Option Strict On Option Explicit On Option Infer On ' Modern class definition Public Class Customer Public Property Id As Integer Public Property Name As String Public Property Email As String ' Constructor Public Sub New ( id As Integer , name As String , email As String ) Me . Id = id Me . Name = name Me . Email = email End Sub End Class ' Modern async method Public Async Function GetCustomerAsync ( id As Integer ) As Task ( Of Customer ) Dim result = Await database . QueryAsync ( Of Customer ) ( "SELECT * FROM Customers WHERE Id = @id" , New With { . id = id } ) Return result . FirstOrDefault ( ) End Function ' LINQ query Dim activeCustomers = From c In customers Where c . IsActive AndAlso c . Balance
0 Order By c . Name Select c Type Safety (Critical) Option Strict On ' ALWAYS at top of every file Option Strict On Option Explicit On Option Infer On ' Why: ' - Option Strict: Prevents implicit narrowing conversions ' - Option Explicit: Requires variable declaration ' - Option Infer: Enables type inference (but still type-safe) Explicit Types vs Inference ' ✅ Good: Explicit when clarity helps Dim customerName As String = GetCustomerName ( id ) Dim count As Integer = GetCount ( ) ' ✅ Good: Inference when type is obvious Dim customer = New Customer ( 1 , "John" , "john@example.com" ) Dim items = New List ( Of String ) From { "a" , "b" , "c" } ' ❌ Bad: Dim without type and no inference Dim data = GetData ( ) ' What type is data? ' ✅ Better: Be explicit Dim data As DataTable = GetData ( ) Nullable Types ' Modern nullable syntax (VB 15.5+) Dim middleName As String ? = Nothing Dim age As Integer ? = Nothing ' Null-conditional operator Dim length As Integer ? = middleName ? . Length ' Null-coalescing operator Dim displayName As String = middleName If Nothing ' Check for null If age IsNot Nothing Then Console . WriteLine ( $"Age: {age.Value}" ) End If ' GetValueOrDefault Dim years As Integer = age . GetValueOrDefault ( 0 ) Modern Language Features String Interpolation ' ✅ Modern (VB 14+) Dim message = $"Customer {customer.Name} has balance {customer.Balance:C}" ' ❌ Old style (avoid) Dim message = String . Format ( "Customer {0} has balance {1:C}" , customer . Name , customer . Balance ) ' ❌ Concatenation (avoid for complex strings) Dim message = "Customer " & customer . Name & " has balance " & customer . Balance . ToString ( "C" ) Lambda Expressions ' Single-line lambda Dim isAdult = Function ( age As Integer ) age
= 18 ' Multi-line lambda Dim calculateTax = Function ( amount As Decimal ) As Decimal Dim rate = If ( amount
10000 , 0.2D , 0.15D ) Return amount * rate End Function ' Lambda in LINQ Dim adults = customers . Where ( Function ( c ) c . Age
= 18 ) . ToList ( ) ' Action lambda (Sub) items . ForEach ( Sub ( item ) Console . WriteLine ( item ) ) Collection Initializers ' List initialization Dim numbers = New List ( Of Integer ) From { 1 , 2 , 3 , 4 , 5 } ' Dictionary initialization Dim config = New Dictionary ( Of String , String ) From { { "ConnectionString" , "Server=..." } , { "Timeout" , "30" } , { "MaxRetries" , "3" } } ' Array initialization Dim names As String ( ) = { "Alice" , "Bob" , "Charlie" } Tuple Support ' Named tuples (VB 15.3+) Function GetCustomerInfo ( id As Integer ) As ( Name As String , Email As String ) Return ( "John Doe" , "john@example.com" ) End Function ' Usage Dim info = GetCustomerInfo ( 1 ) Console . WriteLine ( $"{info.Name}: {info.Email}" ) ' Deconstruction Dim ( customerName , customerEmail ) = GetCustomerInfo ( 1 ) LINQ Patterns Query Syntax vs Method Syntax ' Query syntax (more readable for complex queries) Dim query = From c In customers Where c . IsActive Order By c . Name Select New With { . Name = c . Name , . Email = c . Email } ' Method syntax (more flexible) Dim query = customers _ . Where ( Function ( c ) c . IsActive ) _ . OrderBy ( Function ( c ) c . Name ) _ . Select ( Function ( c ) New With { . Name = c . Name , . Email = c . Email } ) Common LINQ Operations ' Filtering Dim activeCustomers = customers . Where ( Function ( c ) c . IsActive ) . ToList ( ) ' Projection Dim names = customers . Select ( Function ( c ) c . Name ) . ToList ( ) ' Ordering Dim sorted = customers . OrderBy ( Function ( c ) c . Name ) . ThenBy ( Function ( c ) c . Id ) ' Grouping Dim grouped = From c In customers Group c By c . City Into Group Select City , Customers = Group ' Aggregation Dim total = orders . Sum ( Function ( o ) o . Amount ) Dim average = orders . Average ( Function ( o ) o . Amount ) Dim count = customers . Count ( Function ( c ) c . IsActive ) ' First/Single Dim first = customers . FirstOrDefault ( Function ( c ) c . Id = 1 ) Dim single = customers . SingleOrDefault ( Function ( c ) c . Email = email ) ' Any/All Dim hasActive = customers . Any ( Function ( c ) c . IsActive ) Dim allActive = customers . All ( Function ( c ) c . IsActive ) Async/Await Patterns Async Method Declaration ' Return Task(Of T) for async methods with return value Public Async Function GetDataAsync ( ) As Task ( Of String ) Dim result = Await httpClient . GetStringAsync ( url ) Return result End Function ' Return Task for async methods without return value Public Async Function SaveDataAsync ( data As String ) As Task Await File . WriteAllTextAsync ( filePath , data ) End Function ' Async Sub only for event handlers Private Async Sub Button_Click ( sender As Object , e As EventArgs ) Handles Button . Click Await ProcessDataAsync ( ) End Sub Async Best Practices ' ✅ Good: Await all the way Public Async Function ProcessOrderAsync ( orderId As Integer ) As Task ( Of Boolean ) Dim order = Await GetOrderAsync ( orderId ) Await ValidateOrderAsync ( order ) Await SaveOrderAsync ( order ) Return True End Function ' ❌ Bad: Blocking on async (deadlock risk) Public Function ProcessOrder ( orderId As Integer ) As Boolean Dim order = GetOrderAsync ( orderId ) . Result ' Can deadlock! Return True End Function ' ✅ Good: ConfigureAwait(False) in libraries Public Async Function GetDataAsync ( ) As Task ( Of String ) Dim result = Await httpClient . GetStringAsync ( url ) . ConfigureAwait ( False ) Return result End Function ' Parallel async operations Dim tasks = New List ( Of Task ( Of Customer ) ) From { GetCustomerAsync ( 1 ) , GetCustomerAsync ( 2 ) , GetCustomerAsync ( 3 ) } Dim customers = Await Task . WhenAll ( tasks ) Error Handling Try-Catch Patterns ' Modern structured exception handling Try Dim result = Await ProcessDataAsync ( ) Return result Catch ex As ArgumentNullException ' Handle specific exception logger . LogError ( ex , "Null argument in ProcessData" ) Throw Catch ex As HttpRequestException ' Handle another specific exception logger . LogError ( ex , "HTTP request failed" ) Return Nothing Catch ex As Exception ' Catch-all (use sparingly) logger . LogError ( ex , "Unexpected error" ) Throw Finally ' Cleanup (always runs) connection ? . Dispose ( ) End Try Exception Filters ' VB 14+ exception filters Try ProcessData ( ) Catch ex As IOException When ex . Message . Contains ( "file not found" ) ' Handle specific IO error CreateDefaultFile ( ) Catch ex As IOException When ex . Message . Contains ( "access denied" ) ' Handle different IO error RequestPermissions ( ) End Try Custom Exceptions ' Define custom exception Public Class CustomerNotFoundException Inherits Exception Public Property CustomerId As Integer Public Sub New ( customerId As Integer ) MyBase . New ( $"Customer {customerId} not found" ) Me . CustomerId = customerId End Sub Public Sub New ( customerId As Integer , innerException As Exception ) MyBase . New ( $"Customer {customerId} not found" , innerException ) Me . CustomerId = customerId End Sub End Class ' Usage If customer Is Nothing Then Throw New CustomerNotFoundException ( customerId ) End If Property Patterns Auto-Implemented Properties ' Simple auto property Public Property Name As String ' With default value Public Property IsActive As Boolean = True ' Read-only auto property (VB 14+) Public ReadOnly Property Id As Integer ' Can only be set in constructor Public Sub New ( id As Integer ) Me . Id = id End Sub Computed Properties Public Class Customer Public Property FirstName As String Public Property LastName As String ' Computed property Public ReadOnly Property FullName As String Get Return $"{FirstName} {LastName}" End Get End Property ' Property with validation Private _age As Integer Public Property Age As Integer Get Return _age End Get Set ( value As Integer ) If value < 0 Or value
150 Then Throw New ArgumentOutOfRangeException ( NameOf ( Age ) ) End If _age = value End Set End Property End Class Interfaces and Inheritance Interface Definition Public Interface IRepository ( Of T ) Function GetByIdAsync ( id As Integer ) As Task ( Of T ) Function GetAllAsync ( ) As Task ( Of IEnumerable ( Of T ) ) Function AddAsync ( entity As T ) As Task Function UpdateAsync ( entity As T ) As Task Function DeleteAsync ( id As Integer ) As Task End Interface ' Implementation Public Class CustomerRepository Implements IRepository ( Of Customer ) Public Async Function GetByIdAsync ( id As Integer ) As Task ( Of Customer ) _ Implements IRepository ( Of Customer ) . GetByIdAsync Return Await dbContext . Customers . FindAsync ( id ) End Function ' ... other implementations End Class Class Inheritance ' Base class Public MustInherit Class BaseEntity Public Property Id As Integer Public Property CreatedAt As DateTime Public Property UpdatedAt As DateTime Public MustOverride Sub Validate ( ) End Class ' Derived class Public Class Customer Inherits BaseEntity Public Property Name As String Public Property Email As String Public Overrides Sub Validate ( ) If String . IsNullOrWhiteSpace ( Name ) Then Throw New ValidationException ( "Name is required" ) End If If Not Email . Contains ( "@" ) Then Throw New ValidationException ( "Invalid email format" ) End If End Sub End Class Best Practices ✅ DO ' Always use Option Strict On Option Strict On Option Explicit On Option Infer On ' Use modern syntax (LINQ, async/await, string interpolation) Dim activeCustomers = Await customers . Where ( Function ( c ) c . IsActive ) . ToListAsync ( ) Dim message = $"Found {activeCustomers.Count} active customers" ' Use meaningful names Dim customerEmailAddress As String Dim isCustomerActive As Boolean ' Use async/await for I/O operations Public Async Function LoadDataAsync ( ) As Task ( Of Data ) ' Use IDisposable pattern Using connection = New SqlConnection ( connectionString ) ' Use connection End Using ' Use XML comments for public APIs '''
''' Gets a customer by their unique identifier. ''' ''' The customer ID to search for. '''The customer if found, Nothing otherwise. Public Async Function GetCustomerAsync ( customerId As Integer ) As Task ( Of Customer ) ❌ DON'T ' Don't use On Error (use Try-Catch) On Error Resume Next ' Legacy VB6 style - AVOID ' Don't use late binding Dim obj As Object = CreateObject ( "Excel.Application" ) ' Use typed references ' Don't block on async Dim result = GetDataAsync ( ) . Result ' Can deadlock ' Don't use underscores in new code (legacy convention) Private m_customerName As String ' Use camelCase: _customerName ' Don't concatenate strings in loops Dim result As String = "" For Each item In items result & = item ' Use StringBuilder or String.Join Next ' Don't use Hungarian notation Dim strName As String ' Just use: Dim name As String Dim intCount As Integer ' Just use: Dim count As Integer