Attributes question!

[CSharper]

Hi All,

I have seen lot of programs uses attributes.

[Attribute]
public class method()
{
}

I know attribute is nothing but a class derived from Attribute. I
still couldn't wrap my head around when to use and what it does during
run time. Can some one kindly point me to a detailed place where I can
read? Most of the examples are very simple and I don't see any use or
need of those. If you have time, could you kindly explain me what is
this?

Thanks,

 

[Larry Smith]

Hi All,

I have seen lot of programs uses attributes.

[Attribute]
public class method()
{
}

I know attribute is nothing but a class derived from Attribute. I
still couldn't wrap my head around when to use and what it does during
run time. Can some one kindly point me to a detailed place where I can
read? Most of the examples are very simple and I don't see any use or
need of those. If you have time, could you kindly explain me what is
this?

An "attribute" simply represents any piece of information you may want to
store about a given entity (class, method, etc.) that can later be read by
3rd-party tools or the code itself at runtime. Why would you want to do
this? For the same reason you would store information about anything.
Someone might need it. Look at "System.ObsoleteAttribute" as one simple
example. By applying this to any method, you're telling the rest of the
world that the method is now considered obsolete. If you now call this
method in your program for instance, a compiler can detect that the method
is obsolete and display a warning for you. Or perhaps someone wants to write
a utility that will display all obsolete methods being called from your
program simply by reading the assembly itself (since the attribute info is
stored there). And what if you want to add your own information about some
entitry, say, which developer wrote a particular method for instance. You
can create your own "MethodAuthorAttribute" that takes the developers's
employee # (or some other appropriate ID) and this can appplied to every
method in your program. The attrbute can then be used for any number of
reasons. Perhaps you want to dump this to a log at runtime if an unexpected
exception is thrown (for diagnostic purposes). The code can determine which
method was involved and then dump the author's ID out by reading that
method's "MethodAuthorAttribute". Your help staff would then be able to
quickly determine which developer originally wrote the function (or maybe
your company's QA staff uses it during internal testing only). This example
is contrived of course but you get the idea. Have a look at the "Inheritance
Hierarchy" section under the "Attribute" class in MSDN
(http://msdn.microsoft.com/en-us/library/system.attribute.aspx). These are
the native .NET attributes and many are used for obscure purposes but they
still fulfill their role, namely, they provide information about the
entities they apply to (to those who need it).

 

[CSharper]

Hi All,

I have seen lot of programs uses attributes.

[Attribute]
public class method()
{
}

I know attribute is nothing but a class derived from Attribute. I
still couldn't wrap my head around when to use and what it does during
run time. Can some one kindly point me to a detailed place where I can
read? Most of the examples are very simple and I don't see any use or
need of those. If you have time, could you kindly explain me what is
this?

An "attribute" simply represents any piece of information you may want to
store about a given entity (class, method, etc.) that can later be read by
3rd-party tools or the code itself at runtime. Why would you want to do
this? For the same reason you would store information about anything.
Someone might need it. Look at "System.ObsoleteAttribute" as one simple
example. By applying this to any method, you're telling the rest of the
world that the method is now considered obsolete. If you now call this
method in your program for instance, a compiler can detect that the method
is obsolete and display a warning for you. Or perhaps someone wants to write
a utility that will display all obsolete methods being called from your
program simply by reading the assembly itself (since the attribute info is
stored there). And what if you want to add your own information about some
entitry, say, which developer wrote a particular method for instance. You
can create your own "MethodAuthorAttribute" that takes the developers's
employee # (or some other appropriate ID) and this can appplied to every
method in your program. The attrbute can then be used for any number of
reasons. Perhaps you want to dump this to a log at runtime if an unexpected
exception is thrown (for diagnostic purposes). The code can determine which
method was involved and then dump the author's ID out by reading that
method's "MethodAuthorAttribute". Your help staff would then be able to
quickly determine which developer originally wrote the function (or maybe
your company's QA staff uses it during internal testing only). This example
is contrived of course but you get the idea. Have a look at the "Inheritance
Hierarchy" section under the "Attribute" class in MSDN
(http://msdn.microsoft.com/en-us/library/system.attribute.aspx). These are
the native .NET attributes and many are used for obscure purposes but they
still fulfill their role, namely, they provide information about the
entities they apply to (to those who need it).

Thank you very much.

 

[Jeff Johnson]

I have seen lot of programs uses attributes.

[Attribute]
public class method()
{
}

I know attribute is nothing but a class derived from Attribute. I
still couldn't wrap my head around when to use and what it does during
run time.

For the most part (in my experience), attributes have very little to do with
RUN time and much more to do with design time and compile time. The
PropertyGrid control is a big consumer of attributes. You can control the
way properties in the grid behave (such as whether they display at all, or
what editor will be used for them) by decorating them with attributes.

 

[Arne Vajhøj]

I have seen lot of programs uses attributes.

[Attribute]
public class method()
{
}

I know attribute is nothing but a class derived from Attribute. I
still couldn't wrap my head around when to use and what it does during
run time. Can some one kindly point me to a detailed place where I can
read? Most of the examples are very simple and I don't see any use or
need of those. If you have time, could you kindly explain me what is
this?

The attributes of a class are typical used when some other code is
looking at the class via reflection and use the information in the
attributes to do something.

Examples:
- an XML serializer uses the attributes to decide which properties
becomes XML elements and which becomes XML attributes
- an O/R-mappers uses the the attributes to decide on table
names and column names

Arne