When you want to validate values assigned to method parameters, the validation is most often executed at runtime. You do not get any warning that something is broken until you execute a method that is being validated during testing. If you do not execute the method during testing then you are not notified about a possible bug at all.

It would be better to do the validation already at build time. Then you would not need do the testing at all and there is no chance to miss any warning.

This example demonstrates how to use PostSharp Architecture Framework to validate, at build time, that the value passed to a string parameter is a valid string in a managed resource.

The ValidateResourceStringAttribute implements the validation constraint. The ValidateResourceStringAttribute inherits from ReferentialConstraint because you need to validate the usage of the method, not the method itself.

The ValidateConstraint method validates that the [ValidateResourceString(string resourceName)] attribute is used on a parameter of type string, and checks that the resource with resourceName exists in the current project. If the resource with resourceName does not exist in the current project then the ValidateConstraint emits a build warning.

The ValidateCode method first uses the ReflectionSearch.GetMethodsUsingDeclaration method to get a list of all methods invoking the validated method. Then, you use a SyntaxTreeVisitor to analyze bodies of these methods and to check if values assigned to a validated parameter is a valid resource key.

The ValidateResourceStringAttribute constraint can validate just literal or constants passed to a validated parameter. If you pass an expression requiring runtime evaluation to a validate parameter, for example a variable or a method call expression then the validation at the build time cannot work.