Attribute targets and usage in C Sharp (C#) - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is an attribute target in C#?

An attribute target specifies where an attribute can be applied, such as a class, method, property, or assembly.

beginner

How do you specify that an attribute can only be used on methods?

Use [AttributeUsage(AttributeTargets.Method)] above the attribute class definition.

intermediate

What does the AttributeUsage attribute control?

It controls where the custom attribute can be applied and whether it can be applied multiple times or inherited.

intermediate

Can an attribute be applied to multiple targets? How?

Yes, by combining targets using a bitwise OR, for example: [AttributeUsage(AttributeTargets.Class | AttributeTargets.Method)].

beginner

What happens if you apply an attribute to a target not allowed by its AttributeUsage?

The compiler will show an error because the attribute is used on an invalid target.

Which AttributeTargets value allows an attribute to be applied to properties?

A AttributeTargets.Field

B AttributeTargets.Method

C AttributeTargets.Class

D AttributeTargets.Property

AttributeTargets.Property is used to specify that an attribute can be applied to properties.

How do you allow an attribute to be used multiple times on the same target?

A Use multiple attribute declarations

B Set AllowMultiple = true in AttributeUsage

C Set Inherited = true in AttributeUsage

D Use AttributeTargets.All

AllowMultiple = true in AttributeUsage allows applying the attribute multiple times on the same target.

What is the default target if AttributeUsage is not specified?

A All targets

B Class only

C Method only

D Property only

By default, attributes can be applied to all targets if AttributeUsage is not specified.

Which of these is NOT a valid AttributeTargets value?

A AttributeTargets.Interface

B AttributeTargets.Event

C AttributeTargets.Namespace

D AttributeTargets.Parameter

AttributeTargets.Namespace does not exist; namespaces cannot have attributes.

What does setting Inherited = false in AttributeUsage do?

A Prevents derived classes from inheriting the attribute

B Allows multiple attributes on the same target

C Restricts attribute to methods only

D Makes attribute internal

Inherited = false means the attribute is not inherited by derived classes.

Explain how to restrict a custom attribute to be used only on classes and methods.

Think about combining targets with a bitwise OR.

Describe what happens if you try to apply an attribute to a target not allowed by its AttributeUsage.

Consider compiler checks for attribute placement.