Contract.Requires<'TException> Method (Boolean, String)


Specifies a precondition contract for the enclosing method or property, and throws an exception with the provided message if the condition for the contract fails.

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

static member Requires<'TException when 'TException : Exception> : 
        condition:bool *
        userMessage:string -> unit


Type: System.Boolean

The conditional expression to test.

Type: System.String

The message to display if the condition is false.

Type Parameters


The exception to throw if the condition is false.

  • System_CAPS_importantImportant

    You must turn on run-time checking to use the Requires<'TException> method. If run-time checking is turned off, the process will be terminated. To obtain the tools for runtime checking, see Code Contracts on the MSDN DevLabs Web site.

    This method call must be at the beginning of a method or property, before any other code.

  • This contract is exposed to clients; therefore, it must only reference members that are at least as visible as the enclosing method.

  • Use this method instead of the Contract.Requires(Boolean, String) method when you want to throw an exception if the precondition fails.

Universal Windows Platform
Available since 8
.NET Framework
Available since 4.0
Portable Class Library
Supported in: portable .NET platforms
Available since 4.0
Windows Phone Silverlight
Available since 8.0
Windows Phone
Available since 8.1
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