how to casting a object inherit form Form to another object in c# 2.0

[harvie wang]

Hi,
I want to implement a common Form with special interface, such as MovePoint(doubl e,double).
I create a interface first:
namespace ABC.Test
{
public Interface IMyWindowInterf ace
{
void MovePoint(doubl e,double);
}
}
then create a Form inherit form MyWindow:
namespace ABC.Test.A
{
public AWindow:Form,AB C.Test.IMyWindo w
{
public void MovePoint(doubl e x,double y)
{
//do work
}
}
public BWindow:AWindow ,ABC.Test.IMyWi ndow
{
public void MovePoint(doubl e x,double y)
{
//do work
}
}
public void Test()
{
BWindow oB = new BWindow();
AWindow oA = (AWindow)oB; //casting exception
IMyWindow oI = (IMyWindow)oB; //casting exception
AWindow oA = oB as AWindow; // 0k but it's null
IMyWindow oI = oB as IMyWindow;
//why oA == null and oI == null?????
if(oA != null)
{
oA.MovePoint(1. 0d,3.0d);
}
if(oI != null)
{
oI.MovePoint(1. 0d,2.3d);
}

}
}

thanks!

harvie

2006-4-29

[harvie wang]

using System;
using System.Collecti ons;
public interface IA
{
void Add();
}
public class A:IA
{
public void Add()
{
Console.WriteLi ne("A:IA out put");
}
}
public class B:IA
{
public void Add()
{
Console.WriteLi ne("B:IA out put");
}
}
public interface IB
{
void Work();
}

public class C:A,IB
{
new public void Add()
{
Console.WriteLi ne("C:A,IB out put");
}
public void Work()
{
Console.WriteLi ne("C:work");
}
}

public class D:System.Window s.Forms.Form,IA
{
public void Add()
{
Console.WriteLi ne("D out put");
}
}
public class MyClass
{
public static void Main()
{
D d = new D();
IA a = (IA)d;
a.Add();
d.Add();//ok
//d.Show();

A a = new A();
a.Add();
IA ia = (IA)a;
ia.Add();
B b = (B)ia;// compiler error
b.Add();// error
C c = new C();//ok
c.Add();
IA ic = (IA)c;
ic.Add();
IB ib = (IB)c;
ib.Work();
A ca = (A)c;
ca.Add();

RL();
}

#region Helper methods

private static void WL(object text, params object[] args)
{
Console.WriteLi ne(text.ToStrin g(), args);
}

private static void RL()
{
Console.ReadLin e();
}

private static void Break()
{
System.Diagnost ics.Debugger.Br eak();
}

#endregion
}
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we can cast the child class to parent class, and call the parent class's
methods.
但是如果强 制转æ�¢çˆ¶ç±» 为å*�类的è¯� ，å�³ä½¿èƒ½å¤Ÿ 转æ�¢ï¼Œä¹Ÿä¼š å�‘生问题（ 这个在Cï¼‹ï¼ ‹ä¸*å¤§å®¶éƒ½æ˜ Žç™½çš„é�“ç�†ï¼ ‰ï¼›
it's dangerous to cast a child class to parent class.
也å�¯ä»¥æŠŠå*� 类强制转化 为父类的接 å�£ç±»ï¼Œå¹¶è°ƒ 用接å�£ç±»ä¸* 声明的接å�£ ï¼›
we can cast a child class to parent interface, and can invoke the interface.
如果是通过 Asemblyæ��ä¾›çš „å��å°„æœºåˆ¶ç” Ÿæˆ�çš„ç±»åœ¨è¿ ›è¡Œå¼ºåˆ¶è½¬æ� ¢çš„æ—¶å€™ï¼Œåœ ¨C＃2ä¸*有编 译错误，Cï¼ ƒ1ä¸*è¿˜æ²¡æœ‰æ µ‹è¯•ï¼Œæœ‰å…´è ¶£çš„也å�¯ä»¥ç œ‹çœ‹ï¼›
it throw compiler error information in C# 2.0, when i cast a class which
created by assembly reflect.
接下æ�¥çš„é—® 题就是ç*”究 一下plugin技 术，看看人 家怎么实现 的了：）

Hi,
I want to implement a common Form with special interface, such as
MovePoint(doubl e,double).
I create a interface first:
namespace ABC.Test
{
public Interface IMyWindowInterf ace
{
void MovePoint(doubl e,double);
}
}
then create a Form inherit form MyWindow:
namespace ABC.Test.A
{
public AWindow:Form,AB C.Test.IMyWindo w
{
public void MovePoint(doubl e x,double y)
{
//do work
}
}
public BWindow:AWindow ,ABC.Test.IMyWi ndow
{
public void MovePoint(doubl e x,double y)
{
//do work
}
}
public void Test()
{
BWindow oB = new BWindow();
AWindow oA = (AWindow)oB; //casting
exception
IMyWindow oI = (IMyWindow)oB; //casting
exception
AWindow oA = oB as AWindow; // 0k but it's
null
IMyWindow oI = oB as IMyWindow;
//why oA == null and oI == null?????
if(oA != null)
{
oA.MovePoint(1. 0d,3.0d);
}
if(oI != null)
{
oI.MovePoint(1. 0d,2.3d);
}
}
}
thanks!

harvie

2006-4-29

[Greg Young]

> public class B:IA ...

A a = new A();
a.Add();
IA ia = (IA)a;
ia.Add();
B b = (B)ia;// compiler error
b.Add();// error
You are trying to convert an A to a B .. an A is not a B and therefor fails
...

B is always an IA
an IA is not always a B

an A is never a B
"harvie wang" <qu*****@gmail. com> wrote in message
news:5e******** *************** ***@news.micros oft.com... using System;
using System.Collecti ons;
public interface IA
{
void Add();
}
public class A:IA
{
public void Add()
{
Console.WriteLi ne("A:IA out put");
}
}
public class B:IA
{
public void Add()
{
Console.WriteLi ne("B:IA out put");
}
}
public interface IB
{
void Work();
}

public class C:A,IB
{
new public void Add()
{
Console.WriteLi ne("C:A,IB out put");
}
public void Work()
{
Console.WriteLi ne("C:work");
}
}

public class D:System.Window s.Forms.Form,IA
{
public void Add()
{
Console.WriteLi ne("D out put");
}
}
public class MyClass
{
public static void Main()
{
D d = new D();
IA a = (IA)d;
a.Add();
d.Add();//ok
//d.Show();

A a = new A();
a.Add();
IA ia = (IA)a;
ia.Add();
B b = (B)ia;// compiler error
b.Add();// error
C c = new C();//ok
c.Add();
IA ic = (IA)c;
ic.Add();
IB ib = (IB)c;
ib.Work();
A ca = (A)c;
ca.Add();

RL();
}

#region Helper methods

private static void WL(object text, params object[] args)
{
Console.WriteLi ne(text.ToStrin g(), args); }

private static void RL()
{
Console.ReadLin e(); }

private static void Break() {
System.Diagnost ics.Debugger.Br eak();
}

#endregion
}
??????????????? ?,????????;
we can cast the child class to parent class, and call the parent class's
methods.
??????????????? ,??????,??????( ???C++????????? );
it's dangerous to cast a child class to parent class.
??????????????? ??,???????????? ;
we can cast a child class to parent interface, and can invoke the
interface.
?????Asembly??? ??????????????? ???,?C#2??????, C#1??????,????? ????;
it throw compiler error information in C# 2.0, when i cast a class which
created by assembly reflect.
????????????plu gin??,????????? ?:)

Hi,
I want to implement a common Form with special interface, such as
MovePoint(doubl e,double).
I create a interface first:
namespace ABC.Test
{
public Interface IMyWindowInterf ace
{
void MovePoint(doubl e,double);
}
}
then create a Form inherit form MyWindow:
namespace ABC.Test.A
{
public AWindow:Form,AB C.Test.IMyWindo w
{
public void MovePoint(doubl e x,double y)
{
//do work
}
}
public BWindow:AWindow ,ABC.Test.IMyWi ndow
{
public void MovePoint(doubl e x,double y)
{
//do work
}
}
public void Test()
{
BWindow oB = new BWindow();
AWindow oA = (AWindow)oB; //casting
exception
IMyWindow oI = (IMyWindow)oB; //casting
exception
AWindow oA = oB as AWindow; // 0k but it's
null
IMyWindow oI = oB as IMyWindow;
//why oA == null and oI == null?????
if(oA != null)
{
oA.MovePoint(1. 0d,3.0d);
}
if(oI != null)
{
oI.MovePoint(1. 0d,2.3d);
}
}
}
thanks!

harvie

2006-4-29