CA1062: Validate arguments of public methods
TypeName | ValidateArgumentsOfPublicMethods |
CheckId | CA1062 |
Category | Microsoft.Design |
Breaking Change | Non Breaking |
All reference arguments that are passed to externally visible methods should be checked against null. If appropriate, throw a ArgumentNullException when the argument is null.
If a method can be called from an unknown assembly because it is declared public or protected, you should validate all parameters of the method. If the method is designed to be called only by known assemblies, you should make the method internal and apply the InternalsVisibleToAttribute attribute to the assembly that contains the method.
The following example shows a method that violates the rule and a method that satisfies the rule.
Imports System Namespace DesignLibrary Public Class Test ' This method violates the rule. Sub DoNotValidate(ByVal input As String) If input.Length <> 0 Then Console.WriteLine(input) End If End Sub ' This method satisfies the rule. Sub Validate(ByVal input As String) If input Is Nothing Then Throw New ArgumentNullException("input") End If If input.Length <> 0 Then Console.WriteLine(input) End If End Sub End Class End Namespace
using System; namespace DesignLibrary { public class Test { // This method violates the rule. public void DoNotValidate(string input) { if (input.Length != 0) { Console.WriteLine(input); } } // This method satisfies the rule. public void Validate(string input) { if (input == null) { throw new ArgumentNullException("input"); } if (input.Length != 0) { Console.WriteLine(input); } } } }
In Visual Studio 2005, this rule does not detect that parameters are being passed to another method that does the validation.
Public Function Method(ByVal value As String) As String EnsureNotNull(value) ' Fires incorrectly Return value.ToString() End Function Private Sub EnsureNotNull(ByVal value As String) If value Is Nothing Then Throw (New ArgumentNullException("value")) End If End Sub
public string Method(string value) { EnsureNotNull(value); // Fires incorrectly return value.ToString(); } private void EnsureNotNull(string value) { if (value == null) throw new ArgumentNullException("value"); }
Copy constructors that populate field or properties that are reference objects can also violate the CA1062 rule. The violation occurs because the copied object that is passed to the copy constructor might be null (Nothing in Visual Basic). To resolve the violation, use a static (Shared in Visual Basic) method to check that the copied object is not null.
In the following Person class example, the other object that is passed to the Person copy constructor might be null.
public class Person
{
public string Name { get; private set; }
public int Age { get; private set; }
public Person(string name, int age)
{
Name = name;
Age = age;
}
// Copy constructor CA1062 fires because other is dereferenced
// without being checked for null
public Person(Person other)
: this(other.Name, other.Age)
{
}
}
In the following revised Person example, the other object that is passed to the copy constructor is first checked for null in the PassThroughNonNull method.
public class Person
{
public string Name { get; private set; }
public int Age { get; private set; }
public Person(string name, int age)
{
Name = name;
Age = age;
}
// Copy constructor
public Person(Person other)
: this(PassThroughNonNull(other).Name,
PassThroughNonNull(other).Age)
{
}
// Null check method
private static Person PassThroughNonNull(Person person)
{
if (person == null)
throw new ArgumentNullException("person");
return person;
}
}
