blocks|key|733279|text|你的静态方法应该是：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|733280|public+static+class+SimpleUsing
{
++++public+static+void+DoUsing(Action<MyDataContext>+action)
++++{
++++++++using+(MyDataContext+db+=+new+MyDataContext())
+++++++++++action(db);
++++}
}|code-block|syntax|javascript|733281|至：|733282|public+static+class+SimpleUsing
{
++++public+static+TResult+DoUsing<TResult>(Func<MyDataContext,+TResult>+action)
++++{
++++++++using+(MyDataContext+db+=+new+MyDataContext())
+++++++++++return+action(db);
++++}
}|733283|这个答案来自评论，所以我可以提供代码。有关完整的详细信息，请参阅下面@sll的答案。|733284|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]]|$1|G|3|H|5|6|7|Q|8|@]|9|@]|A|$]]|$1|I|3|J|5|D|7|R|8|@]|9|@]|A|$E|F]]|$1|K|3|L|5|6|7|S|8|@]|9|@]|A|$]]|$1|M|3|-4|5|6|7|T|8|@]|9|@]|A|$]]]|N|$]]

Your static method should go from:

<pre><code>public static class SimpleUsing
{
 public static void DoUsing(Action&lt;MyDataContext&gt; action)
 {
 using (MyDataContext db = new MyDataContext())
 action(db);
 }
}
</code></pre>

To:

<pre><code>public static class SimpleUsing
{
 public static TResult DoUsing&lt;TResult&gt;(Func&lt;MyDataContext, TResult&gt; action)
 {
 using (MyDataContext db = new MyDataContext())
 return action(db);
 }
}
</code></pre>

This answer grew out of comments so I could provide code. For a complete elaboration, please see @sll's answer below.

blocks|key|516819|text|您还可以利用lambda或匿名方法可以关闭其封闭作用域中的变量这一事实。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|516820|MyType+result;

SimpleUsing.DoUsing(db+=>+
{
++result+=+db.SomeQuery();+//whatever+returns+the+MyType+result
});+

//do+something+with+result|code-block|syntax|javascript|516821|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|J|8|@]|9|@]|A|$E|F]]|$1|G|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|H|$]]

You can also take advantage of the fact that a lambda or anonymous method can close over variables in its enclosing scope.

<pre><code>MyType result;

SimpleUsing.DoUsing(db =&gt; 
{
 result = db.SomeQuery(); //whatever returns the MyType result
}); 

//do something with result
</code></pre>

blocks|key|516937|text|使用Func而不是Action。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|516938|Action的作用类似于带有T类型参数的空方法，而Func的作用类似于没有参数的函数，它返回T类型的对象。|516939|如果您希望为函数提供参数，请使用Func<TParameter1,+TParameter2,+...,+TReturn>。|516940|entityMap|0|LINK|mutability|MUTABLE|url|https://docs.microsoft.com/pt-br/dotnet/api/system.func-2?view=netframework-4.8|1|https://docs.microsoft.com/pt-br/dotnet/api/system.action-1?view=netframework-4.8|2|3^0|2|4|9|6|2|4|0|9|6|1|0|0|6|P|4|0|6|2|P|4|3|0|G|18|0^^$0|@$1|2|3|4|5|6|7|V|8|@$9|W|A|X|B|C]|$9|Y|A|Z|B|C]]|D|@$9|10|A|11|1|12]|$9|13|A|14|1|15]]|E|$]]|$1|F|3|G|5|6|7|16|8|@$9|17|A|18|B|C]|$9|19|A|1A|B|C]]|D|@$9|1B|A|1C|1|1D]|$9|1E|A|1F|1|1G]]|E|$]]|$1|H|3|I|5|6|7|1H|8|@$9|1I|A|1J|B|C]]|D|@]|E|$]]|$1|J|3|-4|5|6|7|1K|8|@]|D|@]|E|$]]]|K|$L|$5|M|N|O|E|$P|Q]]|R|$5|M|N|O|E|$P|S]]|T|$5|M|N|O|E|$P|S]]|U|$5|M|N|O|E|$P|Q]]]]

Use <a href="https://docs.microsoft.com/pt-br/dotnet/api/system.func-2?view=netframework-4.8" rel="noreferrer"><code>Func&lt;T&gt;</code></a> rather than <a href="https://docs.microsoft.com/pt-br/dotnet/api/system.action-1?view=netframework-4.8" rel="noreferrer"><code>Action&lt;T&gt;</code></a>. 

<a href="https://docs.microsoft.com/pt-br/dotnet/api/system.action-1?view=netframework-4.8" rel="noreferrer"><code>Action&lt;T&gt;</code></a> acts like a void method with parameter of type T, while <a href="https://docs.microsoft.com/pt-br/dotnet/api/system.func-2?view=netframework-4.8" rel="noreferrer"><code>Func&lt;T&gt;</code></a> works like a function with no parameters and which returns an object of type T. 

If you wish to give parameters to your function, use <code>Func&lt;TParameter1, TParameter2, ..., TReturn&gt;</code>.

blocks|key|517095|text|除了ssls回答:对于一个软件，我们调用很多“微方法”来从本地机器上查询这个和那个。有时会出现异常(文件/文件夹不存在等)。为了不重复使用try/catch块，我们使用了带有返回值的ssls方法：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|517096|private+T+ExecuteAndCatch<T>(Func<T>+action,+T+defaultReturn)
{
++++try
++++{
++++++++return+action();
++++}
++++catch+(Exception+ex)
++++{
++++++++Log.e("Exception+during+ExecuteAndCatch",+ex);
++++++++return+defaultReturn;
++++}
}|code-block|syntax|javascript|517097|上面提到的微方法示例：|517098|private+Boolean+CheckKasperskyInstalled()+=>+System.IO.File.Exists(Environment.ExpandEnvironmentVariables(@"%25pf_x86%25\Kaspersky+Lab\Kaspersky+Endpoint+Security+for+Windows\avp.exe"));
private+Boolean+CheckKasperskyRunning()+=>+System.Diagnostics.Process.GetProcessesByName("avp").Length+>+0;|517099|在使用时，我们不再需要关心这些方法是否会因为某种原因抛出异常：|517100|cci+=+new+ComputerComplianceInfo();
cci.KasperskyInstalled+=+ExecuteAndCatch(()+=>+CheckKasperskyInstalled(),+false);
cci.KasperskyRunning+=+ExecuteAndCatch(()+=>+CheckKasperskyRunning(),+false);|517101|entityMap^0|0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|Q|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|R|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|S|8|@]|9|@]|A|$]]|$1|I|3|J|5|D|7|T|8|@]|9|@]|A|$E|F]]|$1|K|3|L|5|6|7|U|8|@]|9|@]|A|$]]|$1|M|3|N|5|D|7|V|8|@]|9|@]|A|$E|F]]|$1|O|3|-4|5|6|7|W|8|@]|9|@]|A|$]]]|P|$]]

In addition to ssls answer: For a software we call a lot of &quot;micro methods&quot; to query this and that from the local machine. Sometimes exceptions appear (file / folder not existing, etc). In order to not repeat our self over and over with try/catch blocks, we used ssls approach with return values:
<pre><code>private T ExecuteAndCatch&lt;T&gt;(Func&lt;T&gt; action, T defaultReturn)
{
 try
 {
 return action();
 }
 catch (Exception ex)
 {
 Log.e(&quot;Exception during ExecuteAndCatch&quot;, ex);
 return defaultReturn;
 }
}
</code></pre>
Example of mentioned micro-methods:
<pre><code>private Boolean CheckKasperskyInstalled() =&gt; System.IO.File.Exists(Environment.ExpandEnvironmentVariables(@&quot;%pf_x86%\Kaspersky Lab\Kaspersky Endpoint Security for Windows\avp.exe&quot;));
private Boolean CheckKasperskyRunning() =&gt; System.Diagnostics.Process.GetProcessesByName(&quot;avp&quot;).Length &gt; 0;
</code></pre>
And when using, we no longer have to care if these Methods might throw an exception for whatever reason:
<pre><code>cci = new ComputerComplianceInfo();
cci.KasperskyInstalled = ExecuteAndCatch(() =&gt; CheckKasperskyInstalled(), false);
cci.KasperskyRunning = ExecuteAndCatch(() =&gt; CheckKasperskyRunning(), false);
</code></pre>

blocks|key|516992|text|我也有这个需求，但是涉及到跨线程的问题--+MainForm中的方法从UserControl中的控件中返回数据。后来，我需要返回一个值，正如@sll所建议的那样，我不得不使用Original+code+was+an+extension+method+that+perform+an+Action委托。|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|516993|在ControlExtensions类中：|516994|+++++public+static+TResult+RunOnUiThread<TResult>(this+Control+@this,+Func<TResult>+code)
++++++++{
++++++++++++if+(@this.InvokeRequired)
++++++++++++{
++++++++++++++++var+toReturn+=+@this.BeginInvoke(code);++++++++++++++++++
++++++++++++++++return+(TResult)@this.EndInvoke(toReturn);
++++++++++++}
++++++++++++else
++++++++++++{
++++++++++++++++return+code.Invoke();
++++++++++++}
+++++++}|code-block|syntax|javascript|516995|此扩展方法从MainForm中的方法调用，从UserControl中的控件获取一些值；在本例中，我从ListBox返回SelectedItem的值：|516996|++++++++++++++++return+UserControl1.listBox1.RunOnUiThread(
++++++++++++++++++++()+=>+UserControl1.listBox1.GetItemText(
++++++++++++++++++++++++++++UserControl1.listBox1.SelectedItem)
++++++++++++++++++++);|516997|entityMap|0|LINK|mutability|MUTABLE|url|https://stackoverflow.com/a/3588137/2752308^0|2F|1O|0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|W|8|@]|9|@$A|X|B|Y|1|Z]]|C|$]]|$1|D|3|E|5|6|7|10|8|@]|9|@]|C|$]]|$1|F|3|G|5|H|7|11|8|@]|9|@]|C|$I|J]]|$1|K|3|L|5|6|7|12|8|@]|9|@]|C|$]]|$1|M|3|N|5|H|7|13|8|@]|9|@]|C|$I|J]]|$1|O|3|-4|5|6|7|14|8|@]|9|@]|C|$]]]|P|$Q|$5|R|S|T|C|$U|V]]]]

I had this need too, but involving cross-thread concerns - Method in MainForm returning data out of a control in an UserControl. <a href="https://stackoverflow.com/a/3588137/2752308">Original code was an extension method that perform an Action</a>; later, I needed to return a value, and as @sll suggested, had to use the Func delegate instead.
In a ControlExtensions class:
<pre><code> public static TResult RunOnUiThread&lt;TResult&gt;(this Control @this, Func&lt;TResult&gt; code)
 {
 if (@this.InvokeRequired)
 {
 var toReturn = @this.BeginInvoke(code); 
 return (TResult)@this.EndInvoke(toReturn);
 }
 else
 {
 return code.Invoke();
 }
 }
</code></pre>
This extension method is called from a method in MainForm, getting some value from a control inside an UserControl; in this example, I'm returning the value of the SelectedItem from a ListBox:
<pre><code> return UserControl1.listBox1.RunOnUiThread(
 () =&gt; UserControl1.listBox1.GetItemText(
 UserControl1.listBox1.SelectedItem)
 );
</code></pre>

In regards to the answer for this question <a href="https://stackoverflow.com/questions/8098950/passing-datacontext-into-action">Passing DataContext into Action()</a>, how do I return a value from action(db)?

<pre><code>SimpleUsing.DoUsing(db =&gt; { 
// do whatever with db 
}); 
</code></pre>

Should be more like:

<pre><code>MyType myType = SimpleUsing.DoUsing&lt;MyType&gt;(db =&gt; { 
// do whatever with db. query buit using db returns MyType.
}); 
</code></pre>

How to return value from Action()?

Windows

关于这个问题的答案，我如何从操作(Db)返回一个值？SimpleUsing.DoUsing(db => { // do whatever with db }); 应该更像这样：MyType myType = SimpleUsing.DoUsing<MyType>(db => { // do whatever with db. query buit using db returns MyType.

问如何从Action()中返回值？
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