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3. Write one or more public constructors. The parameters to the constructor define
the positional parameters of the attribute and will become mandatory when
using the attribute.
4. Declare a public field or property for each named parameter you wish to support.
Named parameters are optional when using the attribute.
Attribute properties and constructor parameters must be of the
following types:
• A sealed primitive type: in other words, bool, byte, char,
double, float, int, long, short, or string
• The Type type
• An enum type
• A one-dimensional array of any of these
When an attribute is applied, it must also be possible for the
compiler to statically evaluate each of the properties or constructor
arguments.
The following class defines an attribute for assisting an automated unit-testing system.
It indicates that a method should be tested, the number of test repetitions, and
a message in case of failure:
[AttributeUsage (AttributeTargets.Method)]
public sealed class TestAttribute : Attribute
{
public int Repetitions;
public string FailureMessage;
public TestAttribute () : this (1) { }
public TestAttribute (int repetitions) { Repetitions = repetitions; }
}
Here’s a Foo class with methods decorated in various ways with the Test attribute:
class Foo
{
[Test]
public void Method1() { ... }
[Test(20)]
public void Method2() { ... }
[Test(20, FailureMessage="Debugging Time!")]
public void Method3() { ... }
}
704 | Chapter 18: Reflection and Metadata