blocks|key|2318383|text|这看起来内联会做得更好。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|2318384|你可以这样做：|2318385|var+requestedObject+=+someObject+as+TheTypeYouWant;|code-block|syntax|javascript|2318386|当你像这样声明一些东西时，你不会得到一个空引用异常。然后你可以只做一个简单的|2318387|if(requestedObject+!=+null){
++++...
}|2318388|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|$]]

This seems like it would be done better inline.

What you can do is something like:

<pre><code>var requestedObject = someObject as TheTypeYouWant;
</code></pre>

When you declare something like so, you will not get a null reference exception. Then you can just do a simple 

<pre><code>if(requestedObject != null){
 ...
}
</code></pre>

blocks|key|2021674|text|使用泛型：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|2021675|T+foobar<T>()+where+T+:+new()
{
++++return+new+T();
}
void+somefunc()
{
++++Guid+g+=+foobar<Guid>();
}|code-block|syntax|javascript|2021676|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|$]]

Use generics:

<pre><code>T foobar&lt;T&gt;() where T : new()
{
 return new T();
}
void somefunc()
{
 Guid g = foobar&lt;Guid&gt;();
}
</code></pre>

blocks|key|720819|text|您可以像这样定义该方法：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|720820|protected+TReturnType+GetAValue<TReturnType>(Object+someObject)+where+TReturnType+:+class
{
+if(someObject+is+TReturnType)+return+(TReturnType)+someObject;
+return+null;
}|code-block|syntax|javascript|720821|或者，如果您不能保证TReturnType是引用类型，您可以不使用泛型约束(TReturnType+:+class)，而返回默认(+TReturnType+)而不是null+-这将返回TReturnType的默认类型，对于int...|720822|entityMap^0|0|0|0^^$0|@$1|2|3|4|5|6|7|K|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|L|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|M|8|@]|9|@]|A|$]]|$1|I|3|-4|5|6|7|N|8|@]|9|@]|A|$]]]|J|$]]

You can define the method like this:

<pre><code>protected TReturnType GetAValue&lt;TReturnType&gt;(Object someObject) where TReturnType : class
{
 if(someObject is TReturnType) return (TReturnType) someObject;
 return null;
}
</code></pre>

Alternatively if you can't guarantee that TReturnType is a reference type you could leave off the generic constraint (TReturnType : class) and return default(TReturnType) instead of null - this would return the default type of TReturnType which would be 0 for an int...

blocks|key|2024790|text|如果您在编译时(在编写代码时)知道类型，则可以使用泛型。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|2024791|如果你只知道运行时的类型(通过类型)，你可以使用Activator类。|offset|length|2024792|entityMap|0|LINK|mutability|MUTABLE|url|http://msdn.microsoft.com/en-us/library/system.activator.aspx^0|0|O|9|0|0^^$0|@$1|2|3|4|5|6|7|N|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|O|8|@]|9|@$D|P|E|Q|1|R]]|A|$]]|$1|F|3|-4|5|6|7|S|8|@]|9|@]|A|$]]]|G|$H|$5|I|J|K|A|$L|M]]]]

If you know the type at compile time (when writing the code) you can use generics.

If you only know the type at runtime (via Type), you can use the <a href="http://msdn.microsoft.com/en-us/library/system.activator.aspx" rel="nofollow noreferrer">Activator</a> class.

blocks|key|909824|text|这种转换可以使用as来完成|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|909825|requestedObject+as+RequestedType|code-block|syntax|javascript|909826|将这个表达式包装在一个方法中并不能买到任何东西|909827|entityMap^0|8|2|0|0|0^^$0|@$1|2|3|4|5|6|7|O|8|@$9|P|A|Q|B|C]]|D|@]|E|$]]|$1|F|3|G|5|H|7|R|8|@]|D|@]|E|$I|J]]|$1|K|3|L|5|6|7|S|8|@]|D|@]|E|$]]|$1|M|3|-4|5|6|7|T|8|@]|D|@]|E|$]]]|N|$]]

Such conversion can be done using <code>as</code> 

<pre><code>requestedObject as RequestedType
</code></pre>

Wrapping this expression in a method does not really buy your anything

blocks|key|2021748|text|在给定的示例中，只需执行以下操作可能会更好：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|2021749|MyClass+val+=+myObject+as+MyClass;|code-block|syntax|javascript|2021750|然而，为了回答你的问题-是的，答案是使用泛型：|2021751|protected+T+GetAValue<T>(object+someObject)
{
++++if+(someObject+is+T)
++++{
++++++++return+(T)someObject;
++++}
++++else
++++{
++++++++//+We+cannot+return+null+as+T+may+not+be+nullable
++++++++//+see+http://stackoverflow.com/questions/302096/how-can-i-return-null-from-a-generic-method-in-c
++++++++return+default(T);+
++++}
}|2021752|在此方法中，T是类型的参数。您可以在代码中以与使用任何其他类型(例如字符串)完全相同的方式使用T，但是请注意，在这种情况下，我们没有对T是什么进行任何限制，因此类型T的对象只具有基本object的属性和方法(GetType()、ToString()等)。|offset|length|style|BOLD|CODE|2021753|显然，我们必须先声明T是什么，然后才能使用它-例如：|2021754|MyClass+val+=+GetAValue<MyClass>(myObject);
string+strVal+=+GetAValue<string>(someObject);|2021755|有关更多信息，请查看MSDN+documentation+on+Generics|2021756|entityMap|0|LINK|mutability|MUTABLE|url|http://msdn.microsoft.com/en-us/library/512aeb7t%2528VS.80%2529.aspx^0|0|0|0|0|8|5|2J|6|2W|9|36|A|0|0|0|A|U|0|0^^$0|@$1|2|3|4|5|6|7|15|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|16|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|17|8|@]|9|@]|A|$]]|$1|I|3|J|5|D|7|18|8|@]|9|@]|A|$E|F]]|$1|K|3|L|5|6|7|19|8|@$M|1A|N|1B|O|P]|$M|1C|N|1D|O|Q]|$M|1E|N|1F|O|Q]|$M|1G|N|1H|O|Q]]|9|@]|A|$]]|$1|R|3|S|5|6|7|1I|8|@]|9|@]|A|$]]|$1|T|3|U|5|D|7|1J|8|@]|9|@]|A|$E|F]]|$1|V|3|W|5|6|7|1K|8|@]|9|@$M|1L|N|1M|1|1N]]|A|$]]|$1|X|3|-4|5|6|7|1O|8|@]|9|@]|A|$]]]|Y|$Z|$5|10|11|12|A|$13|14]]]]

In your given example you are probably better served just doing the following:

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

However to answer your question - yes, the answer is to use generics:

<pre><code>protected T GetAValue&lt;T&gt;(object someObject)
{
 if (someObject is T)
 {
 return (T)someObject;
 }
 else
 {
 // We cannot return null as T may not be nullable
 // see http://stackoverflow.com/questions/302096/how-can-i-return-null-from-a-generic-method-in-c
 return default(T); 
 }
}
</code></pre>

In this method T is a type parameter. You can use T in your code in exactly the same way that you would any other type (for example a string), however note that in this case we haven't placed any restriction on what T is, and so objects of type T only have the properties and methods of the base <code>object</code> (<code>GetType()</code>, <code>ToString()</code> etc...)

We must obviously declare what T is before we can use it - for example:

<pre><code>MyClass val = GetAValue&lt;MyClass&gt;(myObject);
string strVal = GetAValue&lt;string&gt;(someObject);
</code></pre>

For more information take a look at the <a href="http://msdn.microsoft.com/en-us/library/512aeb7t%28VS.80%29.aspx" rel="noreferrer">MSDN documentation on Generics</a>

blocks|key|909939|text|我认为您实际上可能正在寻找一种Convert.ChangeType机制。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|909940|private+static+object+ChangeTypeTo<T>(this+object+value)
{
++++if+(value+==+null)
++++++++return+null;

++++Type+underlyingType+=+typeof+(T);
++++if+(underlyingType+==+null)
++++++++throw+new+ArgumentNullException("value");

++++if+(underlyingType.IsGenericType+&&+
+++++++++++underlyingType.GetGenericTypeDefinition().Equals(typeof+(Nullable<>)))
++++{
++++++++var+converter+=+new+NullableConverter(underlyingType);
++++++++underlyingType+=+converter.UnderlyingType;
++++}

++++//+Guid+convert
++++if+(underlyingType+==+typeof+(Guid))
++++{
++++++++return+new+Guid(value.ToString());
++++}

++++//+Check+for+straight+conversion+or+value.ToString+conversion
++++var+objType+=+value.GetType();

++++//+If+this+is+false,+lets+hope+value.ToString+can+convert+otherwise+exception
++++bool+objTypeAssignable2typeT+=+underlyingType.IsAssignableFrom(objType);

++++//+Do+conversion
++++return+objTypeAssignable2typeT+?+Convert.ChangeType(value,+underlyingType)
++++++++++++:+Convert.ChangeType(value.ToString(),+underlyingType);
}|code-block|syntax|javascript|909941|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|$]]

I think you might actually be looking for a Convert.ChangeType mechanism.

<pre><code>private static object ChangeTypeTo&lt;T&gt;(this object value)
{
 if (value == null)
 return null;

 Type underlyingType = typeof (T);
 if (underlyingType == null)
 throw new ArgumentNullException("value");

 if (underlyingType.IsGenericType &amp;&amp; 
 underlyingType.GetGenericTypeDefinition().Equals(typeof (Nullable&lt;&gt;)))
 {
 var converter = new NullableConverter(underlyingType);
 underlyingType = converter.UnderlyingType;
 }

 // Guid convert
 if (underlyingType == typeof (Guid))
 {
 return new Guid(value.ToString());
 }

 // Check for straight conversion or value.ToString conversion
 var objType = value.GetType();

 // If this is false, lets hope value.ToString can convert otherwise exception
 bool objTypeAssignable2typeT = underlyingType.IsAssignableFrom(objType);

 // Do conversion
 return objTypeAssignable2typeT ? Convert.ChangeType(value, underlyingType)
 : Convert.ChangeType(value.ToString(), underlyingType);
}
</code></pre>

This seems like it would be possible. 

<pre><code>protected SameObjectTypeAsInputParameterObjectType GetAValue(someObject,TypeOrReturnObjectYouWant){

//check to see if someObject is null, if not, cast it and send the cast back

}
</code></pre>

C# Is it possible to pass a type into a method and have the method return an object of that type?

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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这似乎是可能的。protected SameObjectTypeAsInputParameterObjectType GetAValue(someObject,TypeOrReturnObjectYouWant){//check to see if someObject is null, if not, cast it...

问C#是否可以将一个类型传递给一个方法，然后让该方法返回该类型的对象？
EN

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问C#是否可以将一个类型传递给一个方法，然后让该方法返回该类型的对象？EN