blocks|key|1136012|text|is关键字检查其左侧的值是否为右侧类型的实例。例如：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1136013|if(obj+is+string)
{
+++++...
}|code-block|syntax|javascript|1136014|请注意，在这种情况下，您必须使用额外的显式强制转换来将obj转换为字符串。|1136015|as关键字用于强制转换可为nullable的类型。如果指定的值不是指定类型的实例，则返回null。例如：|1136016|string+str+=+obj+as+string;
if(str+!=+null)
{
+++++...
}|1136017|entityMap^0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|O|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|P|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|Q|8|@]|9|@]|A|$]]|$1|I|3|J|5|6|7|R|8|@]|9|@]|A|$]]|$1|K|3|L|5|D|7|S|8|@]|9|@]|A|$E|F]]|$1|M|3|-4|5|6|7|T|8|@]|9|@]|A|$]]]|N|$]]

The is keyword checks whether the value on its left side is an instance of the type on the right side. For example:

<pre><code>if(obj is string)
{
 ...
}
</code></pre>

Note that in this case you'll have to use an extra explicit cast to get obj as string.

The as keyword is used to cast nullable types. If the specified value is not an instance of the specified type, null is returned. For example:

<pre><code>string str = obj as string;
if(str != null)
{
 ...
}
</code></pre>

blocks|key|1135847|text|我会说:在线阅读MSDN，但它是这样的：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1135848|is运算符检查对象是否与给定类型兼容，计算结果为布尔值:+true或false。|1135849|as运算符永远不会抛出异常。|1135850|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|$]]

I would say: read MSDN online, but here it is:

The is operator checks whether an object is compatible with a given type, and the result of the evaluation is a Boolean: true or false. 

The as operator will never throw an exception.

blocks|key|1136170|text|Is运算符，一个强制转换，如果成功则返回true。如果强制转换失败，则返回false。使用它，您无法捕获转换后的变量。此运算符在检查if语句中的类型时最有用，而expressions.The+is-cast仅在不需要进一步使用所产生的变量时才是理想的|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1136171|就像演员阵容一样。有了它，我们可以获得性能，并避免在强制转换无效时出现异常。当无法进行强制转换时，返回Null。对于引用类型，建议使用as-cast。它既快又快，safe.We可以针对null测试结果变量，然后使用它。这消除了额外的强制转换|1136172|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|F|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|G|8|@]|9|@]|A|$]]|$1|D|3|-4|5|6|7|H|8|@]|9|@]|A|$]]]|E|$]]

Is operator , a cast, returns true if it succeeds. It returns false if the cast fails. With it, you cannot capture the converted variable. This operator is most useful when checking types in if-statements and expressions.The is-cast is only ideal if the resulting variable will not be needed for further use

As is a cast. With it, we gain performance and avoid exceptions when a cast is invalid. Null is returned when the cast is impossible. For reference types, the as-cast is recommended. It is both fast and safe.We can test the resulting variable against null and then use it. This eliminates extra casts

blocks|key|1135939|text|As运算符类似于强制转换，但如果失败，则返回null而不是异常。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1135940|Is运算符用于检查一个对象是否与某个类型兼容。它通常用在If语句中。|1135941|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|F|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|G|8|@]|9|@]|A|$]]|$1|D|3|-4|5|6|7|H|8|@]|9|@]|A|$]]]|E|$]]

The As operator is similar to a cast, but returns null instead of an exception if it fails.

And the Is operator is used to check if one object is compatible with a certain type. It's usually used in If statements.

blocks|key|921523|text|is：is运算符用于检查对象的运行时类型是否与给定类型兼容|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|921524|as：as运算符用于执行兼容类型之间的转换。|921525|object+s+=+"this+is+a+test";
string+str=string.Empty;
if(+s+is+string)
++++str+=+s+as+string;|code-block|syntax|javascript|921526|entityMap|0|LINK|mutability|MUTABLE|url|http://msdn.microsoft.com/en-us/library/scekt9xw%2528v=VS.71%2529.aspx|1|http://msdn.microsoft.com/en-us/library/cscsdfbt%2528v=VS.71%2529.aspx^0|0|2|0|2|0|0|0|2|0|2|1|0|0^^$0|@$1|2|3|4|5|6|7|W|8|@$9|X|A|Y|B|C]]|D|@$9|Z|A|10|1|11]]|E|$]]|$1|F|3|G|5|6|7|12|8|@$9|13|A|14|B|C]]|D|@$9|15|A|16|1|17]]|E|$]]|$1|H|3|I|5|J|7|18|8|@]|D|@]|E|$K|L]]|$1|M|3|-4|5|6|7|19|8|@]|D|@]|E|$]]]|N|$O|$5|P|Q|R|E|$S|T]]|U|$5|P|Q|R|E|$S|V]]]]

<a href="http://msdn.microsoft.com/en-us/library/scekt9xw%28v=VS.71%29.aspx" rel="nofollow"><code>is</code></a>: The is operator is used to check whether the run-time type of an object is compatible with a given type

<a href="http://msdn.microsoft.com/en-us/library/cscsdfbt%28v=VS.71%29.aspx" rel="nofollow"><code>as</code></a>: The as operator is used to perform conversions between compatible types. 

<pre><code>object s = "this is a test";
string str=string.Empty;
if( s is string)
 str = s as string;
</code></pre>

blocks|key|1136102|text|看看下面的youtube视频，它以更具说明性和可视化的方式解释了其中的不同之处：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1136103|https://www.youtube.com/watch?v=IKmRtJcRX_I|offset|length|1136104|下面是长长的答案和代码解释。|1136105|“is”关键字对于检查对象是否与某个类型兼容非常有用。例如，在下面的代码中，我们检查“ocust”对象是否是“Customer”类的类型。|1136106|object+ocust+=+new+Customer();

if+(ocust+is+Customer)
{+|code-block|syntax|javascript|1136107|“AS”关键字有助于完成从一种类型到另一种类型的转换。例如，在下面的代码中，我们将对象转换为字符串数据类型。如果“AS”关键字不能进行类型转换，它将返回NULL。|1136108|object+o+=+"somestring";
string+str+=+o+as+string;|1136109|entityMap|0|LINK|mutability|MUTABLE|url^0|0|0|17|0|0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|Z|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|10|8|@]|9|@$D|11|E|12|1|13]]|A|$]]|$1|F|3|G|5|6|7|14|8|@]|9|@]|A|$]]|$1|H|3|I|5|6|7|15|8|@]|9|@]|A|$]]|$1|J|3|K|5|L|7|16|8|@]|9|@]|A|$M|N]]|$1|O|3|P|5|6|7|17|8|@]|9|@]|A|$]]|$1|Q|3|R|5|L|7|18|8|@]|9|@]|A|$M|N]]|$1|S|3|-4|5|6|7|19|8|@]|9|@]|A|$]]]|T|$U|$5|V|W|X|A|$Y|C]]]]

Have a look at the below youtube video which explains the difference in a more demonstrative and visual way :- 

<a href="https://www.youtube.com/watch?v=IKmRtJcRX_I" rel="nofollow">https://www.youtube.com/watch?v=IKmRtJcRX_I</a> 

Below goes the long answer with code explanation.

“IS” keyword is useful to check if objects are compatible with a type. For instance in the below code we are checking if “ocust” object is a type of “Customer” class.

<pre><code>object ocust = new Customer();

if (ocust is Customer)
{ 
</code></pre>

“AS” keyword helps to do conversion from one type to other type. For instance in the below code we are converting object to a string data type. If the “AS” keyword is not able to type cast it returns NULL.

<pre><code>object o = "somestring";
string str = o as string;
</code></pre>

blocks|key|921643|text|MyClass+myObject+=+(MyClass)+obj;|type|code-block|depth|inlineStyleRanges|entityRanges|data|syntax|javascript|921644|vs|unstyled|921645|MyClass+myObject+=+obj+as+MyClass;|921646|如果obj不是MyClass，则第二个函数将返回null，而不是抛出类类型转换异常。|921647|is将只返回true或false|921648|entityMap^0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|O|8|@]|9|@]|A|$B|C]]|$1|D|3|E|5|F|7|P|8|@]|9|@]|A|$]]|$1|G|3|H|5|6|7|Q|8|@]|9|@]|A|$B|C]]|$1|I|3|J|5|F|7|R|8|@]|9|@]|A|$]]|$1|K|3|L|5|F|7|S|8|@]|9|@]|A|$]]|$1|M|3|-4|5|F|7|T|8|@]|9|@]|A|$]]]|N|$]]

<pre><code>MyClass myObject = (MyClass) obj;
</code></pre>

vs

<pre><code>MyClass myObject = obj as MyClass;
</code></pre>

The second will return null if obj isn't a MyClass, rather than throw a class cast exception.

is will only return true or false

blocks|key|921711|text|IS和AS都用于安全类型转换|type|unstyled|depth|inlineStyleRanges|entityRanges|data|921712|IS+Keyword-->检查给定对象的类型是否与新对象类型兼容。它从不抛出异常。这是一个布尔型type..returns，可以为true或false|921713|`student+stud+=+new+student(){}
if(stud+is+student){}+//+It+returns+true+//+let+say+boys+as+derived+class
if(stud+is+boys){}//+It+returns+false+since+stud+is+not+boys+type
+//this+returns+true+when,
student+stud+=+new+boys()+//+this+return+true+for+both+if+conditions.`|code-block|syntax|javascript|921714|AS关键字:检查给定对象的类型是否与新对象类型兼容。如果给定对象与新对象兼容，则返回非null，否则返回null。这会抛出一个异常。|921715|`student+stud+=+new+student(){}
+//+let+say+boys+as+derived+class
boys+boy+=+stud+as+boys;//this+returns+null+since+we+cant+convert+stud+type+from+base+class+to+derived+class
student+stud+=+new+boys()
boys+boy+=+stud+as+boys;//+this+returns+not+null+since+the+obj+is+pointing+to+derived+class`|921716|entityMap^0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|O|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|P|8|@]|9|@]|A|$]]|$1|D|3|E|5|F|7|Q|8|@]|9|@]|A|$G|H]]|$1|I|3|J|5|6|7|R|8|@]|9|@]|A|$]]|$1|K|3|L|5|F|7|S|8|@]|9|@]|A|$G|H]]|$1|M|3|-4|5|6|7|T|8|@]|9|@]|A|$]]]|N|$]]

<h2>Both IS and AS are used for Safe Type Casting</h2>

IS Keyword-->
checks whether the type of an given object is compatible with the new object type. It Never Throws an exception. This is a Boolean type..returns either true or false

<pre><code>`student stud = new student(){}
if(stud is student){} // It returns true // let say boys as derived class
if(stud is boys){}// It returns false since stud is not boys type
 //this returns true when,
student stud = new boys() // this return true for both if conditions.`
</code></pre>

AS Keyword:
checks whether the type of an given object is compatible with the new object type. It returns non-null if given object is compatible with new one, else null.. This throws an exception.

<pre><code>`student stud = new student(){}
 // let say boys as derived class
boys boy = stud as boys;//this returns null since we cant convert stud type from base class to derived class
student stud = new boys()
boys boy = stud as boys;// this returns not null since the obj is pointing to derived class`
</code></pre>

Please tell what is the difference between <code>is</code> and <code>as</code> keyword in C#

Difference between is and as keyword

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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请告诉我C#中的is和as关键字有什么区别

问is和as关键字的区别
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