blocks|key|1498792|text|Using在留下using-block之后调用Dispose()，即使代码抛出异常。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|1498793|因此，您通常将using用于需要清理的类，如IO。|1498794|所以，这个using代码块：|1498795|using+(MyClass+mine+=+new+MyClass())
{
++mine.Action();
}|code-block|syntax|javascript|1498796|会做同样的事情：|1498797|MyClass+mine+=+new+MyClass();
try
{
++mine.Action();
}
finally
{
++if+(mine+!=+null)
++++mine.Dispose();
}|1498798|使用using更短，也更容易阅读。|1498799|entityMap^0|0|5|8|5|N|9|0|7|5|0|0|0|0|0|2|5|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|6|7|13|8|@$9|14|A|15|B|C]]|D|@]|E|$]]|$1|H|3|I|5|6|7|16|8|@]|D|@]|E|$]]|$1|J|3|K|5|L|7|17|8|@]|D|@]|E|$M|N]]|$1|O|3|P|5|6|7|18|8|@]|D|@]|E|$]]|$1|Q|3|R|5|L|7|19|8|@]|D|@]|E|$M|N]]|$1|S|3|T|5|6|7|1A|8|@$9|1B|A|1C|B|C]]|D|@]|E|$]]|$1|U|3|-4|5|6|7|1D|8|@]|D|@]|E|$]]]|V|$]]

<code>Using</code> calls <code>Dispose()</code> after the <code>using</code>-block is left, even if the code throws an exception.

So you usually use <code>using</code> for classes that require cleaning up after them, like IO.

So, this using block:

<pre><code>using (MyClass mine = new MyClass())
{
 mine.Action();
}
</code></pre>

would do the same as:

<pre><code>MyClass mine = new MyClass();
try
{
 mine.Action();
}
finally
{
 if (mine != null)
 mine.Dispose();
}
</code></pre>

Using <code>using</code> is way shorter and easier to read.

blocks|key|1713892|text|将代码放在using块中可确保在控制离开该块时立即释放(尽管不一定是回收)对象。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1713893|entityMap^0|0^^$0|@$1|2|3|4|5|6|7|D|8|@]|9|@]|A|$]]|$1|B|3|-4|5|6|7|E|8|@]|9|@]|A|$]]]|C|$]]

Placing code in a using block ensures that the objects are disposed (though not necessarily collected) as soon as control leaves the block.

blocks|key|1498868|text|如果该类型实现了IDisposable，它会自动释放该类型。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1498869|给定：|1498870|public+class+SomeDisposableType+:+IDisposable
{
+++...implmentation+details...
}|code-block|syntax|javascript|1498871|这些是等效的：|1498872|SomeDisposableType+t+=+new+SomeDisposableType();
try+{
++++OperateOnType(t);
}
finally+{
++++if+(t+!=+null)+{
++++++++((IDisposable)t).Dispose();
++++}
}|1498873|using+(SomeDisposableType+u+=+new+SomeDisposableType())+{
++++OperateOnType(u);
}|1498874|第二个更容易阅读和维护。|1498875|1498876|从C#+8开始，有一个new+syntax+for+using可以让代码更具可读性：|offset|length|style|CODE|1498877|using+var+x+=+new+SomeDisposableType();|1498878|它没有自己的{+}块，使用的范围是从声明点到声明它的块的末尾。这意味着你可以避免像这样的事情：|1498879|string+x+=+null;
using(var+someReader+=+...)
{
++x+=+someReader.Read();
}|1498880|并拥有以下内容：|1498881|using+var+someReader+=+...;
string+x+=+someReader.Read();|1498882|entityMap|0|LINK|mutability|MUTABLE|url|https://docs.microsoft.com/en-us/dotnet/csharp/whats-new/csharp-8#using-declarations^0|0|0|0|0|0|0|0|0|Q|5|B|K|0|0|0|6|3|0|0|0|0^^$0|@$1|2|3|4|5|6|7|1F|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|1G|8|@]|9|@]|A|$]]|$1|D|3|E|5|F|7|1H|8|@]|9|@]|A|$G|H]]|$1|I|3|J|5|6|7|1I|8|@]|9|@]|A|$]]|$1|K|3|L|5|F|7|1J|8|@]|9|@]|A|$G|H]]|$1|M|3|N|5|F|7|1K|8|@]|9|@]|A|$G|H]]|$1|O|3|P|5|6|7|1L|8|@]|9|@]|A|$]]|$1|Q|3|-4|5|6|7|1M|8|@]|9|@]|A|$]]|$1|R|3|S|5|6|7|1N|8|@$T|1O|U|1P|V|W]]|9|@$T|1Q|U|1R|1|1S]]|A|$]]|$1|X|3|Y|5|F|7|1T|8|@]|9|@]|A|$G|H]]|$1|Z|3|10|5|6|7|1U|8|@$T|1V|U|1W|V|W]]|9|@]|A|$]]|$1|11|3|12|5|F|7|1X|8|@]|9|@]|A|$G|H]]|$1|13|3|14|5|6|7|1Y|8|@]|9|@]|A|$]]|$1|15|3|16|5|F|7|1Z|8|@]|9|@]|A|$G|H]]|$1|17|3|-4|5|6|7|20|8|@]|9|@]|A|$]]]|18|$19|$5|1A|1B|1C|A|$1D|1E]]]]

If the type implements IDisposable, it automatically disposes that type.
Given:
<pre><code>public class SomeDisposableType : IDisposable
{
 ...implmentation details...
}
</code></pre>
These are equivalent:
<pre><code>SomeDisposableType t = new SomeDisposableType();
try {
 OperateOnType(t);
}
finally {
 if (t != null) {
 ((IDisposable)t).Dispose();
 }
}
</code></pre>
 
<pre><code>using (SomeDisposableType u = new SomeDisposableType()) {
 OperateOnType(u);
}
</code></pre>
The second is easier to read and maintain.
<hr />
Since C# 8 there is a <a href="https://docs.microsoft.com/en-us/dotnet/csharp/whats-new/csharp-8#using-declarations" rel="noreferrer">new syntax for <code>using</code></a> that may make for more readable code:
<pre><code>using var x = new SomeDisposableType();
</code></pre>
It doesn't have a <code>{ }</code> block of its own and the scope of the using is from the point of declaration to the end of the block it is declared in. It means you can avoid stuff like:
<pre><code>string x = null;
using(var someReader = ...)
{
 x = someReader.Read();
}
</code></pre>
And have this:
<pre><code>using var someReader = ...;
string x = someReader.Read();
</code></pre>

blocks|key|1498913|text|它实际上只是一些语法糖，不需要您显式地调用Dispose来实现IDisposable。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1498914|entityMap^0|0^^$0|@$1|2|3|4|5|6|7|D|8|@]|9|@]|A|$]]|$1|B|3|-4|5|6|7|E|8|@]|9|@]|A|$]]]|C|$]]

It is really just some syntatic sugar that does not require you to explicity call Dispose on members that implement IDisposable.

blocks|key|1713949|text|using+(B+a+=+new+B())
{
+++DoSomethingWith(a);
}|type|code-block|depth|inlineStyleRanges|entityRanges|data|syntax|javascript|1713950|等同于|unstyled|1713951|B+a+=+new+B();
try
{
++DoSomethingWith(a);
}
finally
{
+++((IDisposable)a).Dispose();
}|1713952|entityMap^0|0|0|0^^$0|@$1|2|3|4|5|6|7|K|8|@]|9|@]|A|$B|C]]|$1|D|3|E|5|F|7|L|8|@]|9|@]|A|$]]|$1|G|3|H|5|6|7|M|8|@]|9|@]|A|$B|C]]|$1|I|3|-4|5|F|7|N|8|@]|9|@]|A|$]]]|J|$]]

<pre><code>using (B a = new B())
{
 DoSomethingWith(a);
}
</code></pre>

is equivalent to

<pre><code>B a = new B();
try
{
 DoSomethingWith(a);
}
finally
{
 ((IDisposable)a).Dispose();
}
</code></pre>

blocks|key|1498957|text|using语句获取一个或多个资源，执行一条语句，然后释放资源。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1498958|entityMap^0|0^^$0|@$1|2|3|4|5|6|7|D|8|@]|9|@]|A|$]]|$1|B|3|-4|5|6|7|E|8|@]|9|@]|A|$]]]|C|$]]

The using statement obtains one or more resources, executes a statement, and then disposes of the resource.

blocks|key|1714016|text|using语句用于处理实现IDisposable接口的C#中的对象。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|1714017|IDisposable接口有一个名为Dispose的公共方法，用于释放对象。当我们使用using语句时，我们不需要显式地处理代码中的对象，using语句会处理它。|1714018|using+(SqlConnection+conn+=+new+SqlConnection())
{

}|code-block|syntax|javascript|1714019|当我们使用上面的代码块时，在内部生成的代码如下：|1714020|SqlConnection+conn+=+new+SqlConnection()+
try
{

}
finally
{
++++//+calls+the+dispose+method+of+the+conn+object
}|1714021|有关更多细节，请阅读：Understanding+the+'using'+statement+in+C#。|1714022|entityMap|0|LINK|mutability|MUTABLE|url|http://www.codeproject.com/KB/cs/tinguusingstatement.aspx^0|D|B|0|0|B|I|7|0|0|0|0|B|15|0|0^^$0|@$1|2|3|4|5|6|7|10|8|@$9|11|A|12|B|C]]|D|@]|E|$]]|$1|F|3|G|5|6|7|13|8|@$9|14|A|15|B|C]|$9|16|A|17|B|C]]|D|@]|E|$]]|$1|H|3|I|5|J|7|18|8|@]|D|@]|E|$K|L]]|$1|M|3|N|5|6|7|19|8|@]|D|@]|E|$]]|$1|O|3|P|5|J|7|1A|8|@]|D|@]|E|$K|L]]|$1|Q|3|R|5|6|7|1B|8|@]|D|@$9|1C|A|1D|1|1E]]|E|$]]|$1|S|3|-4|5|6|7|1F|8|@]|D|@]|E|$]]]|T|$U|$5|V|W|X|E|$Y|Z]]]]

The using statement is used to work with an object in C# that implements the <code>IDisposable</code> interface. 

The <code>IDisposable</code> interface has one public method called <code>Dispose</code> that is used to dispose of the object. When we use the using statement, we don't need to explicitly dispose of the object in the code, the using statement takes care of it.

<pre><code>using (SqlConnection conn = new SqlConnection())
{

}
</code></pre>

When we use the above block, internally the code is generated like this:

<pre><code>SqlConnection conn = new SqlConnection() 
try
{

}
finally
{
 // calls the dispose method of the conn object
}
</code></pre>

For more details read: <a href="http://www.codeproject.com/KB/cs/tinguusingstatement.aspx" rel="noreferrer">Understanding the 'using' statement in C#</a>.

blocks|key|1714069|text|还要注意，通过using实例化的对象在using块中是只读的。请参考官方的C#参考here。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|1714070|entityMap|0|LINK|mutability|MUTABLE|url|http://msdn.microsoft.com/en-us//library/yh598w02.aspx^0|7|5|15|4|0|0^^$0|@$1|2|3|4|5|6|7|N|8|@$9|O|A|P|B|C]]|D|@$9|Q|A|R|1|S]]|E|$]]|$1|F|3|-4|5|6|7|T|8|@]|D|@]|E|$]]]|G|$H|$5|I|J|K|E|$L|M]]]]

Also take note that the object instantiated via <code>using</code> is read-only within the using block. Refer to the official C# reference <a href="http://msdn.microsoft.com/en-us//library/yh598w02.aspx" rel="noreferrer">here</a>.

What is the purpose of the <code>Using</code> block in C#? How is it different from a local variable?

What is the C# Using block and why should I use it?

C#中Using块的用途是什么？它与局部变量有什么不同？

问C#使用块是什么?我为什么要使用它？
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