Getting started with Visual Basic .NET Language Console Array Visual Basic 14.0 Features Extension methods Reflection Looping Enum Threading Dictionaries File Handling Short-Circuiting Operators (AndAlso - OrElse)Task-based asynchronous pattern LINQ Data Access Disposable objects Operators Declaring variables Classes Lists Date Introduction to Syntax Option Strict NullReferenceException FTP server Error Handling OOP Keywords Working with Windows Forms File/Folder Compression ByVal and ByRef keywords Type conversion Option Explicit Option Infer GDI+Google Maps in a Windows Form BackgroundWorker Connection Handling Using BackgroundWorker Generics Multithreading Unit Testing in VB.NET Reading compressed textfile on-the-fly Conditions Recursion Using Statement WPF XAML Data Binding WinForms SpellCheckBox Debugging your application Functions Using axWindowsMediaPlayer in VB.Net Random

NullReferenceException

Remarks:

NullReferenceException is thrown whenever a variable is empty and one of its method/properties are referenced. To avoid this, be sure all variables are initialized correctly (new operator), and all methods returns a non-null value.

Uninitialized variable

BAD CODE

Dim f As System.Windows.Forms.Form
f.ShowModal()

GOOD CODE

Dim f As System.Windows.Forms.Form = New System.Windows.Forms.Form
' Dim f As New System.Windows.Forms.Form ' alternative syntax
f.ShowModal()

EVEN BETTER CODE (Ensure proper disposal of IDisposable object more info)

Using f As System.Windows.Forms.Form = New System.Windows.Forms.Form
' Using f As New System.Windows.Forms.Form ' alternative syntax
    f.ShowModal()
End Using

Empty Return

Function TestFunction() As TestClass
    Return Nothing
End Function

BAD CODE

TestFunction().TestMethod()

GOOD CODE

Dim x = TestFunction()
If x IsNot Nothing Then x.TestMethod()

14.0

Null Conditional Operator

TestFunction()?.TestMethod()

Contributors

Topic Id: 4076

Example Ids: 14196,14197

This site is not affiliated with any of the contributors.