в 15:31, 26 мая 2010

2010-05-26T15:31:53Z

Admin: 1 версия

2010-05-26T12:17:26Z

1 версия

Новая страница

=="is" operator for value data type: int, long and float==

<source lang="csharp">class MainClass
{
public static void Main()
{
int myInt = 0;
bool compatible = myInt is int;
System.Console.WriteLine("myInt is int = " + compatible);
compatible = myInt is long;
System.Console.WriteLine("myInt is long = " + compatible);
compatible = myInt is float;
System.Console.WriteLine("myInt is float = " + compatible);
}
}</source>
<pre class=codeResult>myInt is int = True
myInt is long = False
myInt is float = False</pre>

==is operator in class hiearchy==

<source lang="csharp">using System;

class A {}
class B : A {}

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

if(a is A)
Console.WriteLine("a is an A");
if(b is A)
Console.WriteLine("b is an A because it is derived from A");
if(a is B)
Console.WriteLine("This won"t display -- a not derived from B");
if(b is B)
Console.WriteLine("B is a B");
if(a is object)
Console.WriteLine("a is an object");
}
}</source>
<pre class=codeResult>a is an A
b is an A because it is derived from A
B is a B
a is an object</pre>

==Test if someObject is, or is derived from, a TextReader using the is operator==

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

if (someObject is TextReader)
{
Console.WriteLine(
"is: someObject is a TextReader or a derived class");
}
}
}</source>
<pre class=codeResult>is: someObject is a TextReader or a derived class</pre>

==Type operators: Is==

Testing a Type with "is".
You can determine whether an object is of a certain type by using the "is" operator.
Its general form is shown here:

<source lang="csharp">expr is type</source>

==Use is in Console.WriteLine==

<source lang="csharp">using System;
public class MainClass
{
static void Main() {
String derivedObj = "Dummy";
Object baseObj1 = new Object();
Object baseObj2 = derivedObj;
Console.WriteLine( "baseObj2 {0} String", baseObj2 is String ? "is" : "isnot" );
Console.WriteLine( "baseObj1 {0} String", baseObj1 is String ? "is" : "isnot" );
Console.WriteLine( "derivedObj {0} Object", derivedObj is Object ? "is" : "isnot" );
}
}</source>
<pre class=codeResult>baseObj2 is String
baseObj1 isnot String
derivedObj is Object</pre>

==Use "is" to avoid an invalid cast.==

<source lang="csharp">using System;

class A {}
class B : A {}

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

if(a is B)
b = (B) a;
}
}</source>

==Working with Interfaces: is operator==

<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);
// scale the object here.
}

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

private string text;
}
class Test
{
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)
{
if (d is Printable)
{
Printable scalable = (Printable) d;
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>

← Предыдущая	Версия 15:31, 26 мая 2010
(нет различий)

Csharp/CSharp Tutorial/Operator/is - История изменений

в 15:31, 26 мая 2010

Admin: 1 версия