• Article

Contract.Invariant Method (Boolean, String)

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Specifies an invariant contract for the enclosing class, and displays a message if the condition for the contract fails.

Namespace:  System.Diagnostics.Contracts
Assembly:  mscorlib (in mscorlib.dll)

Syntax

'Declaration
<ConditionalAttribute("CONTRACTS_FULL")> _
Public Shared Sub Invariant ( _
    condition As Boolean, _
    userMessage As String _
)

[ConditionalAttribute("CONTRACTS_FULL")]
public static void Invariant(
    bool condition,
    string userMessage
)

Parameters

  • userMessage
    Type: System.String
    The message to display if the condition is false.

Remarks

Invariant contracts are contained within a method that is identified by the ContractInvariantMethodAttribute attribute; typically, the method is named ObjectInvariant.

  • This contract can be specified only in a dedicated invariant method that is declared on a class.

  • This contract is not exposed to clients; therefore, it may reference members that are less visible than the enclosing method.

  • You must use the binary rewriter for run-time enforcement of this invariant.

  • Invariants are conditionally defined on the CONTRACTS FULL symbol. During run-time checking, invariants are checked at the end of each public method. If an invariant mentions a public method in the same class, the invariant check that would normally happen at the end of that public method is disabled and checked only at the end of the outermost method call to that class. This also happens if the class is re-entered because of a call to a method on another class.

Version Information

Silverlight

Supported in: 5, 4

Platforms

For a list of the operating systems and browsers that are supported by Silverlight, see Supported Operating Systems and Browsers.