As stated in "Learning C# 3.0: Master the fundamentals of C# 3.0"
General Scenario: When a head of state dies, the President of the United States typically does not have time to attend the funeral
personally. Instead, he dispatches a delegate. Often this delegate is
the Vice President, but sometimes the VP is unavailable and the
President must send someone else, such as the Secretary of State or
even the First Lady. He does not want to “hardwire” his delegated
authority to a single person; he might delegate this responsibility to
anyone who is able to execute the correct international protocol.
The President defines in advance what responsibility will be delegated
(attend the funeral), what parameters will be passed (condolences,
kind words), and what value he hopes to get back (good will). He then
assigns a particular person to that delegated responsibility at
“runtime” as the course of his presidency progresses.
In programming Scenario: You are often faced with situations where you need to execute a particular action, but you don’t know in
advance which method, or even which object, you’ll want to call upon
to execute it.
For Example: A button might not know which object or objects need to be notified. Rather than wiring the button to a particular
object, you will connect the button to a delegate and then resolve
that delegate to a particular method when the program executes.
与恶龙缠斗过久,自身亦成为恶龙；凝视深渊过久,深渊将回以凝视…
