How to mark a method as obsolete or deprecated?

To mark as obsolete with a warning:

[Obsolete]
private static void SomeMethod()

You get a warning when you use it:

And with IntelliSense:

If you want a message:

[Obsolete("My message")]
private static void SomeMethod()

Here's the IntelliSense tool tip:

Finally if you want the usage to be flagged as an error:

[Obsolete("My message", true)]
private static void SomeMethod()

When used this is what you get:

Note: Use the message to tell people what they should use instead, not why it is obsolete.

With ObsoleteAttribute you can mark a method as deprecated. It has three constructors:

1. [Obsolete]: is a no parameter constructor and is a default using this attribute.
2. [Obsolete(string message)]: in this format you can get message of why this method is deprecated.
3. [Obsolete(string message, bool error)]: in this format message is very explicit but error means, in compilation time, compiler must be showing error and cause to fail compiling or not.

For dependency injected methods, Apply the [Obsolete("description")] attribute to the declaration rather than implementation (:doh: moment for me)