CA2208: Instantiate argument exceptions correctly

Cause

When a method has a parameter, and it throws an exception type that is, or derives from, ArgumentException, it is expected to call a constructor accepting a paramName parameter correctly. Possible causes include the following situations:

• A call is made to the default (parameterless) constructor of an exception type that is, or derives from, ArgumentException that also has a constructor that accepts a paramName parameter.
• An incorrect string argument is passed to a parameterized constructor of an exception type that is, or derives from, ArgumentException. For example, the paramName argument doesn't match the name of one of the method's parameters.
• A parameter name is passed for the message argument of the constructor of an exception type that is, or derives from, ArgumentException.

Rule description

Instead of calling the default constructor, call one of the constructor overloads that allows a more meaningful exception message to be provided. The exception message should target the developer and clearly explain the error condition and how to correct or avoid the exception.

The signatures of the one and two string constructors of ArgumentException and its derived types are not consistent with respect to the position message and paramName parameters. Make sure these constructors are called with the correct string arguments. The signatures are as follows:

• ArgumentException(string message)
• ArgumentException(string message, string paramName)
• ArgumentNullException(string paramName)
• ArgumentNullException(string paramName, string message)
• ArgumentOutOfRangeException(string paramName)
• ArgumentOutOfRangeException(string paramName, string message)
• DuplicateWaitObjectException(string parameterName)
• DuplicateWaitObjectException(string parameterName, string message)

How to fix violations

To fix a violation of this rule, call a constructor that takes a message, a parameter name, or both, and make sure the arguments are proper for the type of ArgumentException being called.

When to suppress warnings

It's safe to suppress a warning from this rule only if a parameterized constructor is called with the correct string arguments.

Suppress a warning

If you just want to suppress a single violation, add preprocessor directives to your source file to disable and then re-enable the rule.

#pragma warning disable CA2208 // The code that's violating the rule is on this line. #pragma warning restore CA2208 

To disable the rule for a file, folder, or project, set its severity to none in the configuration file.

[*.{cs,vb}] dotnet_diagnostic.CA2208.severity = none 

For more information, see How to suppress code analysis warnings.

Configure code to analyze

Use the following option to configure which parts of your codebase to run this rule on.

• Include specific API surfaces

You can configure this option for just this rule, for all rules it applies to, or for all rules in this category (Design) that it applies to. For more information, see Code quality rule configuration options.

Include specific API surfaces

You can configure which parts of your codebase to run this rule on, based on their accessibility, by setting the api_surface option. For example, to specify that the rule should run only against the non-public API surface, add the following key-value pair to an .editorconfig file in your project:

dotnet_code_quality.CAXXXX.api_surface = private, internal 

By default, the CA2208 rule applies to all API surfaces (public, internal, and private).

Example

The following code shows a constructor that incorrectly instantiates an instance of ArgumentNullException.

public class Book { public Book(string title) { Title = title ?? throw new ArgumentNullException("All books must have a title.", nameof(title)); } public string Title { get; } } 

Public Class Book Private ReadOnly _Title As String Public Sub New(ByVal title As String) ' Violates this rule (constructor arguments are switched) If (title Is Nothing) Then Throw New ArgumentNullException("title cannot be a null reference (Nothing in Visual Basic)", "title") End If _Title = title End Sub Public ReadOnly Property Title() Get Return _Title End Get End Property End Class 

The following code fixes the previous violation by switching the constructor arguments.

public class Book { public Book(string title) { Title = title ?? throw new ArgumentNullException(nameof(title), "All books must have a title."); } public string Title { get; } } 

Public Class Book Private ReadOnly _Title As String Public Sub New(ByVal title As String) If (title Is Nothing) Then Throw New ArgumentNullException("title", "title cannot be a null reference (Nothing in Visual Basic)") End If _Title = title End Sub Public ReadOnly Property Title() Get Return _Title End Get End Property End Class 

The following code shows a method that incorrectly throws ArgumentNullException with a paramName that doesn't match any of the method's parameters. The rule fires because description is a local variable, not a method parameter.

public class Product { public string? Description { get; set; } public string Name { get; set; } = string.Empty; } public class Example { // Violates CA2208: 'description' is not a parameter of this method. public void ProcessProduct(Product product) { string? description = product.Description; if (description is null) { throw new ArgumentNullException(nameof(description), $"Product named {product.Name} had no description!"); } // Process description... } } 

Public Class Product Public Property Description As String Public Property Name As String = String.Empty End Class Public Class Example ' Violates CA2208: 'description' is not a parameter of this method. Public Sub ProcessProduct(ByVal product As Product) Dim description As String = product.Description If description Is Nothing Then Throw New ArgumentNullException(NameOf(description), $"Product named {product.Name} had no description!") End If ' Process description... End Sub End Class 

The following code fixes the previous violation by using InvalidOperationException instead, which is appropriate when an object's state is invalid.

public class Product { public string? Description { get; set; } public string Name { get; set; } = string.Empty; } public class Example { // Fixed: Use InvalidOperationException for invalid object state. public void ProcessProduct(Product product) { string? description = product.Description; if (description is null) { throw new InvalidOperationException($"Product named {product.Name} had no description!"); } // Process description... } } 

Public Class Product Public Property Description As String Public Property Name As String = String.Empty End Class Public Class Example ' Fixed: Use InvalidOperationException for invalid object state. Public Sub ProcessProduct(ByVal product As Product) Dim description As String = product.Description If description Is Nothing Then Throw New InvalidOperationException($"Product named {product.Name} had no description!") End If ' Process description... End Sub End Class 

Related rules

• CA1507: Use nameof in place of string