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==as operator in class hearchy==

<source lang="csharp">using System;

class A {}
class B : A {}

class MainClass {
public static void Main() {
A a = new A();
B b = new B();

b = a as B; // cast, if possible

if(b==null)
Console.WriteLine("Cast b = (B) a is NOT allowed.");
else
Console.WriteLine("Cast b = (B) a is allowed");
}
}</source>
<pre class=codeResult>Cast b = (B) a is NOT allowed.</pre>

==The As Operator for custom class type==

<source lang="csharp">using System;
interface Printable
{
void MarginX(float factor);
void MarginY(float factor);
}
public class Component
{
public Component() {}
}
public class TextField: Component, Printable
{
public TextField(string text)
{
this.text = text;
}
// implementing Printable.MarginX()
public void MarginX(float factor)
{
Console.WriteLine("MarginX: {0} {1}", text, factor);
}

// implementing Printable.MarginY()
public void MarginY(float factor)
{
Console.WriteLine("MarginY: {0} {1}", text, factor);
}

private string text;
}
class MainClass
{
public static void Main()
{
Component[] dArray = new Component[100];

dArray[0] = new Component();
dArray[1] = new TextField("A");
dArray[2] = new TextField("B");

foreach (Component d in dArray)
{
Printable scalable = d as Printable;
if (scalable != null)
{
scalable.MarginX(0.1F);
scalable.MarginY(10.0F);
}
}
}
}</source>
<pre class=codeResult>MarginX: A 0.1
MarginY: A 10
MarginX: B 0.1
MarginY: B 10</pre>

==Use the "as" operator to perform a safe cast==

<source lang="csharp">using System;
using System.IO;
class MainClass
{
public static void Main()
{
Object someObject = new StringReader("This is a StringReader");

StringReader reader = someObject as StringReader;
if (reader != null)
{
Console.WriteLine("as: someObject is a StringReader");
}
}
}</source>
<pre class=codeResult>as: someObject is a StringReader</pre>

==Using as==

<p>You can use the as operator to cast without raising an exception if the cast fails.</p>
<p>The general form:</p>

<source lang="csharp">expr as type</source>
<OL><LI>expr is the expression being cast to type.</LI><LI>On succeed, a reference to type is returned.</LI><LI>Otherwise, a null reference is returned.</LI></OL>

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в 15:31, 26 мая 2010

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