blocks|key|1172966|text|一些区别是：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1172967|1172968|委托允许multicasting+(即，委托类型的多个元素在其调用列表中)。|unordered-list-item|offset|length|1172969|委托允许调用者和被调用的特定函数之间的某种程度的解耦。|1172970|上面的委托允许将委托发送到对订阅者和实现一无所知的函数中。然后，您就有了一个发布者/订阅者pattern.|1172971|Delegates的实现，它是创建事件的垫脚石，它使用委托来通知0到N个订阅者某个特定事件已经发生的事实，并将描述事件详细信息的数据传递给所有订阅者。|1172972|1172973|entityMap|0|LINK|mutability|MUTABLE|url|http://msdn.microsoft.com/en-us/library/ms173175%2528v=vs.80%2529.aspx^0|0|0|4|C|0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|W|8|@]|9|@]|A|$]]|$1|B|3|-4|5|6|7|X|8|@]|9|@]|A|$]]|$1|C|3|D|5|E|7|Y|8|@]|9|@$F|Z|G|10|1|11]]|A|$]]|$1|H|3|I|5|E|7|12|8|@]|9|@]|A|$]]|$1|J|3|K|5|E|7|13|8|@]|9|@]|A|$]]|$1|L|3|M|5|E|7|14|8|@]|9|@]|A|$]]|$1|N|3|-4|5|6|7|15|8|@]|9|@]|A|$]]|$1|O|3|-4|5|6|7|16|8|@]|9|@]|A|$]]]|P|$Q|$5|R|S|T|A|$U|V]]]]

Some differences are:

<ul>
<li>Delegates allow for <a href="http://msdn.microsoft.com/en-us/library/ms173175%28v=vs.80%29.aspx" rel="nofollow">multicasting</a> (i.e., more than one element of the delegate type in its invocation list). </li>
<li>Delegates allow for some level of decoupling between the invoker and the specific function being invoked.</li>
<li>The above allows delegates to be sent into functions that know nothing about the subscribers and the implementation. Then, you have an implementation of the publisher / subscribers pattern.</li>
<li>Delegates are a stepping stone to creating Events, which use delegates for notification of 0-N subscribers of the fact that a particular event has occurred along with passing data describing the event details to all subscribers.</li>
</ul>

blocks|key|1173034|text|不同之处在于，您告诉CalcMyTotal使用哪种方法--函数组合。CalcMyTotal不知道所涉及的任何一种方法(或者您可以想象出的任何其他方法)--也不需要知道。它所需要知道的就是“你给我一种做某事的方法，我就会去做”。在一个更典型的例子中，CalcMyTotal所做的不仅仅是调用方法，例如：|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|1173035|var+somethingTricky+=+LotsOfWork(amt);
var+intermediateValue+=+calcTotal(somethingTricky);
return+SomeMoreWork(intermediateValue);|code-block|syntax|javascript|1173036|这里的要点是:调用者不需要知道CalcMyTotal内部发生了什么-它只需要提供一些机制来“计算总数”；CalcMyTotal也不需要知道涉及到的任何机制。您可以将其视为单方法接口。|1173037|为了完整性，您还可以这样做(可能更清楚)：|1173038|public+static+double+CalcMyTotal(double+amt,+Func<double,double>+calcTotal)+{...}|1173039|(注意Func<...>的用法)，并使用lambda语法调用：|1173040|double+tot1+=+CalcMyTotal(100.34,+amt+=>+amt+*+0.014);|1173041|entityMap^0|A|B|Y|B|3G|B|0|0|F|B|1G|B|0|0|0|3|9|0|0^^$0|@$1|2|3|4|5|6|7|W|8|@$9|X|A|Y|B|C]|$9|Z|A|10|B|C]|$9|11|A|12|B|C]]|D|@]|E|$]]|$1|F|3|G|5|H|7|13|8|@]|D|@]|E|$I|J]]|$1|K|3|L|5|6|7|14|8|@$9|15|A|16|B|C]|$9|17|A|18|B|C]]|D|@]|E|$]]|$1|M|3|N|5|6|7|19|8|@]|D|@]|E|$]]|$1|O|3|P|5|H|7|1A|8|@]|D|@]|E|$I|J]]|$1|Q|3|R|5|6|7|1B|8|@$9|1C|A|1D|B|C]]|D|@]|E|$]]|$1|S|3|T|5|H|7|1E|8|@]|D|@]|E|$I|J]]|$1|U|3|-4|5|6|7|1F|8|@]|D|@]|E|$]]]|V|$]]

The difference is that you are telling <code>CalcMyTotal</code> which method to use - functional composition. <code>CalcMyTotal</code> doesn't know about either of the methods involved (or any other you could dream up) - and doesn't need to. All it needs to know is "you give me a way to do something, I'll do it". In a more typical example, <code>CalcMyTotal</code> would be doing something a bit more than just calling the method, for example:

<pre><code>var somethingTricky = LotsOfWork(amt);
var intermediateValue = calcTotal(somethingTricky);
return SomeMoreWork(intermediateValue);
</code></pre>

The point here: the caller doesn't need to know what goes on inside <code>CalcMyTotal</code> - it just needs to supply some mechanism to "calc total"; and <code>CalcMyTotal</code> doesn't need to know anything about the mechanism involved. You could think of it as a single-method interface.

For completeness, you could also do that (perhaps more clearly) as:

<pre><code>public static double CalcMyTotal(double amt, Func&lt;double,double&gt; calcTotal) {...}
</code></pre>

(note the <code>Func&lt;...&gt;</code> usage), and invoke with lambda syntax:

<pre><code>double tot1 = CalcMyTotal(100.34, amt =&gt; amt * 0.014);
</code></pre>

blocks|key|1182365|text|这是因为你正在处理微不足道的例子……|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1182366|想象一下，如果你是一个库的设计者，你希望其他人将不同的方法传递到CalcMyTotal中。|1182367|或者..。也许更简单，当有人单击用户界面上的按钮时，您希望能够插入不同的功能，以便在单击按钮时执行不同的操作|1182368|entityMap^0|0|0|0^^$0|@$1|2|3|4|5|6|7|H|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|I|8|@]|9|@]|A|$]]|$1|D|3|E|5|6|7|J|8|@]|9|@]|A|$]]|$1|F|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|G|$]]

Its because you are dealing with trivial examples.....

Imagine if you are a designer of a library, you want other people to pass different methods into CalcMyTotal.

or..... perhaps simpler, when someone clicks a button on a user interface, you want to be able to plug different functions in to do different things when the button is clicked

blocks|key|4958184|text|当您需要传递对方法的引用时，委托是最有用的。示例包括events+in+C#和sorting+with+a+custom+comparator。|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|4958185|后者的一个示例：|4958186|class+Thing
{
++++private+int+value;

++++public+static+int+CompareTwoThings(Thing+one,+Thing+other)
++++{
++++++++if+(one.value+<+other.value)+return+-1;
++++++++if+(one.value+>+other.value)+return+1;
++++++++return+0;
++++}
}

//+elsewhere
List<Thing>+things+=+GetSomeThings();
things.Sort(Thing.CompareTwoThings);|code-block|syntax|javascript|4958187|当然，在这种情况下，您确实应该让Thing实现IComparable，但这只是一个示例，说明如何将委托用作自定义排序函数。|style|CODE|4958188|entityMap|0|LINK|mutability|MUTABLE|url|http://msdn.microsoft.com/en-us/library/aa645739(v=vs.71).aspx|1|http://msdn.microsoft.com/en-us/library/w56d4y5z.aspx^0|Q|C|0|13|W|1|0|0|0|G|5|N|B|0^^$0|@$1|2|3|4|5|6|7|Y|8|@]|9|@$A|Z|B|10|1|11]|$A|12|B|13|1|14]]|C|$]]|$1|D|3|E|5|6|7|15|8|@]|9|@]|C|$]]|$1|F|3|G|5|H|7|16|8|@]|9|@]|C|$I|J]]|$1|K|3|L|5|6|7|17|8|@$A|18|B|19|M|N]|$A|1A|B|1B|M|N]]|9|@]|C|$]]|$1|O|3|-4|5|6|7|1C|8|@]|9|@]|C|$]]]|P|$Q|$5|R|S|T|C|$U|V]]|W|$5|R|S|T|C|$U|X]]]]

Delegates are most useful when you need to pass a reference to a method around. Examples include <a href="http://msdn.microsoft.com/en-us/library/aa645739(v=vs.71).aspx" rel="nofollow">events in C#</a> and <a href="http://msdn.microsoft.com/en-us/library/w56d4y5z.aspx" rel="nofollow">sorting with a custom comparator</a>.

An example of the latter:

<pre><code>class Thing
{
 private int value;

 public static int CompareTwoThings(Thing one, Thing other)
 {
 if (one.value &lt; other.value) return -1;
 if (one.value &gt; other.value) return 1;
 return 0;
 }
}

// elsewhere
List&lt;Thing&gt; things = GetSomeThings();
things.Sort(Thing.CompareTwoThings);
</code></pre>

Of course, in this case you really should have <code>Thing</code> implement <code>IComparable</code> instead, but this is just an example of how you can use a delegate as a custom sort function.

I finally understood how to use delegates, but can't really figure out why use them instead of method calls. I found this answer pasted bellow, but I can't figure out what is a big difference between those two, because I could simply say

<pre><code>double tot1 = CalcTotalMethod1(100.34);
double tot2 = CalcTotalMethod2(100.34);
</code></pre>

instead of 

<pre><code>double tot1 = CalcMyTotal(100.34, CalcTotalMethod1);
double tot2 = CalcMyTotal(100.34, CalcTotalMethod2);
</code></pre>

This is a example:

<pre><code>public static double CalcTotalMethod1(double amt)
{
 return amt * .014;
}

public static double CalcTotalMethod2(double amt)
{
 return amt * .056 + 42.43;
}


public delegate double calcTotalDelegate(double amt);

public static double CalcMyTotal(double amt, calcTotalDelegate calcTotal)
{
 return calcTotal(amt);
}

double tot1 = CalcMyTotal(100.34, CalcTotalMethod1);
double tot2 = CalcMyTotal(100.34, CalcTotalMethod2);
Console.WriteLine(tot1);
Console.WriteLine(tot2);
</code></pre>

Delegates in C# (un)explained example - looks same as method call would appear

翻译质量差，导致语言生硬或混乱。

没有提供实际的解决方法或示例。

解答不清晰，无法理解或解决问题。

页面排版不美观，阅读体验差。

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我终于明白了如何使用委托，但我真的搞不懂为什么要用委托而不是方法调用。我发现这个答案贴得很低，但我不知道这两个之间有什么大的区别，因为我可以简单地说double tot1 = CalcTotalMethod1(100.34);double tot2 = CalcTotalMethod2(100.34);而不是doubl...

问C# (Un)中的委托解释示例-看起来与出现的方法调用相同
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