C#

joelbasson wrote:

"Unable to cast object of type 'ResponseProcessingCSP' to 'ResponseProcessingCSP'

joelbasson wrote:

ResponseProcessingCSP inherits from type IResponseProcessingCSP

Control _control = new Control();
Button _button = _control as Button;
if(_button!=null)
{
}
else
{
	//this part of the code is executed, cause _button = null;
}

Button _button = new Button();
Control _control = _button;
Button _newbutton = _control as Button;
if(_newbutton!=null)
{
	//this part of the code is executed, cause _newbutton != null;
}
else
{
}

Martin# wrote:

But it was instanciated as IResponseProcessingCSP, and you can not Up'cast' it , I think!

Martin# wrote:

You should use the 'as' operator, which will not throw an exception, if the casting is not possible!

if ( o is typeA ) do something with (typeA) o
else if ( o is typeB ) do something with (typeB) o
else if ( o is typeC ) do something with (typeC) o
...

typeA tempA ;
typeB tempB ;
typeC tempC ;
...

if ( ( tempA = o as typeA ) != null ) do something with tempA
else if ( ( tempB = o as typeB ) != null ) do something with tempB
else if ( ( tempC = o as typeC ) != null ) do something with tempC
...

Colin Angus Mackay wrote:

You can't instantiate an interface.

Colin Angus Mackay wrote:

Perhaps there would be a situation where you do want an exception. Perhaps a case where the situation should never exist and so will be an exceptional case. Use "as" only when the posibility is frequent and expected.

Martin# wrote:

Colin Angus Mackay wrote:
You can't instantiate an interface.

True

Martin# wrote:

The method returns an IResponsableProcessingCSP instance

Colin Angus Mackay wrote:

You cannot have an instance of an interface. You can only have a reference to one.

Colin Angus Mackay wrote:

The instance is of some concrete object that happens to implement the interface.

Martin# wrote:

But it was instanciated as IResponseProcessingCSP

ITheInterface iface = new ClassThatImplementsITheInterface();

public interface ITest
{
    bool PTest
    {
        get;
        set;
    }
}

public class CTest_A : System.Windows.Forms.Control, ITest
{
    public CTest_A()
    {
    }
    #region ITest Member
    private bool _ptest=false;
    public bool PTest
    {
        get
        {
            return _ptest;
        }
        set
        {
            _ptest = value;
        }
    }
    #endregion

    private bool _padditional_A=false;
    public bool PAdditional_A
    {
        get
        {
            return _padditional_A;
        }
        set
        {
            _padditional_A = value;
        }
    }
}

public class CTest_B : System.Windows.Forms.Control, ITest
{
    public CTest_B()
    {
    }

    #region ITest Member
    private bool _ptest=false;
    public bool PTest
    {
        get
        {
            return _ptest;
        }
        set
        {
            _ptest = value;
        }
    }
    #endregion

    private bool _padditional_B=false;
    public bool PAdditional_B
    {
        get
        {
            return _padditional_B;
        }
        set
        {
            _padditional_B = value;
        }
    }
}

CTest_B C_B = new CTest_B();

private ITest GetIReference()
{
    return C_B as ITest;
}

public Form1()
{
    InitializeComponent();

    CTest_A C_A = (CTest_A)GetIReference(); //Throws an invalid cast exception here
        }

Vikram A Punathambekar wrote:

you are essentially trying to cast a CTest_B object to a CTest_A reference. This will work only if CTest_A is an ancestor of CTest_B or a cast is defined. You haven't, so it bombs.

Vikram A Punathambekar wrote:

Try making GetIReference() return an instance of CTest_A (don't change the sig!) and you will see what I meant

Vikram A Punathambekar wrote:

Greetings to Österreich.

Type1 reference1 = new Type2();

Type1 reference2 = reference1;

Vikram A Punathambekar wrote:

I'm sure you know this; it's probably just that you weren't using the correct terminology.

Vikram A Punathambekar wrote:

Don't worry, your English is far better than my German

Vikram A Punathambekar wrote:

Second, when you say
Type1 reference1 = new Type2();

Vikram A Punathambekar wrote:

Therefore, assuming Type2 inherits from Type1 (directly or indirectly, it doesn't matter), a subsequent cast like
Type1 reference2 = reference1;
will always work. (You don't even need a cast!)

Martin# wrote:

Vikram A Punathambekar wrote:
Second, when you say
Type1 reference1 = new Type2();

Did I?

Vikram A Punathambekar wrote:

Hee hee, when I said "When you say..." I did not imply that you said those words. I was presenting a hypothetical scenario, not saying you said something.

Vikram A Punathambekar wrote:

About the casting, I think there's just a misunderstanding. Forget all we talked about in this thread and keep up the good work.

Vikram A Punathambekar wrote:

Forget all we talked about in this thread and keep up the good work.

Vikram A Punathambekar wrote:

BTW, there are far too many languages spoken in India to list

Martin# wrote:

This perfectly fitts to you Signature (Which allways make me laugh when reading)

Martin# wrote:

I choosed the one with the most percentage

Martin# wrote:

Here is the link to the German Wikipedia page, for your training.

Vikram A Punathambekar wrote:

Is it true that there is no neuter gender in German and everything is male/female?