How to reference an event ?

[Stig]

I have declared an interface containing an event.

The class implementing the interface should implement the event by
referring to an event on an object owns, instead of implementing the
event, but this does not seem to be possible, because I get the
compiler error:

The event 'SelectionChanged' can only appear on the left hand side of
+= or -=.

Example:

interface I
{
event MyEventHandler EventName;
}

public class C1
{
public event MyEventHandler EventName;
}

public class C2 : I
{
private C1 c1;

public event MyEventHandler EventName = c1.EventName;

}

How can the above functionality be achieved. I need this functionality
because I am implementing the Model View Presenter pattern as described
on Martin Fowlers webpage, and here it is suggested to use an interface
of the view, to make unit testing of the GUI behaviour possible.

Regards Stig Nielsson

[Vadym Stetsyak]

"The class implementing the interface should implement the event by
referring to an event on an object owns"

afaik event cannot be implemented, it can be called ( in the class that owns
it ) or subscribed to it by the class that has the object with the event.

--
Vadym Stetsyak aka Vadmyst

"Stig" <st****@gmail.com> wrote in message
news:11*********************@z14g2000cwz.googlegro ups.com...

I have declared an interface containing an event.

The class implementing the interface should implement the event by
referring to an event on an object owns, instead of implementing the
event, but this does not seem to be possible, because I get the
compiler error:

The event 'SelectionChanged' can only appear on the left hand side of
+= or -=.

Example:

interface I
{
event MyEventHandler EventName;
}

public class C1
{
public event MyEventHandler EventName;
}

public class C2 : I
{
private C1 c1;

public event MyEventHandler EventName = c1.EventName;

}

How can the above functionality be achieved. I need this functionality
because I am implementing the Model View Presenter pattern as described
on Martin Fowlers webpage, and here it is suggested to use an interface
of the view, to make unit testing of the GUI behaviour possible.

Regards Stig Nielsson

[Ignacio Machin \( .NET/ C# MVP \)]

Hi,

You need to do nothing in the class, think of it as if the event was
declared in the class, you can use it without making any further reference
to it.

cheers,

--
Ignacio Machin,
ignacio.machin AT dot.state.fl.us
Florida Department Of Transportation

"Stig" <st****@gmail.com> wrote in message
news:11*********************@z14g2000cwz.googlegro ups.com...

I have declared an interface containing an event.

The class implementing the interface should implement the event by
referring to an event on an object owns, instead of implementing the
event, but this does not seem to be possible, because I get the
compiler error:

The event 'SelectionChanged' can only appear on the left hand side of
+= or -=.

Example:

interface I
{
event MyEventHandler EventName;
}

public class C1
{
public event MyEventHandler EventName;
}

public class C2 : I
{
private C1 c1;

public event MyEventHandler EventName = c1.EventName;

}

How can the above functionality be achieved. I need this functionality
because I am implementing the Model View Presenter pattern as described
on Martin Fowlers webpage, and here it is suggested to use an interface
of the view, to make unit testing of the GUI behaviour possible.

Regards Stig Nielsson

[Jon Skeet [C# MVP]]

Stig <st****@gmail.com> wrote:

I have declared an interface containing an event.

The class implementing the interface should implement the event by
referring to an event on an object owns, instead of implementing the
event, but this does not seem to be possible, because I get the
compiler error:

The event 'SelectionChanged' can only appear on the left hand side of
+= or -=.

Example:

interface I
{
event MyEventHandler EventName;
}

public class C1
{
public event MyEventHandler EventName;
}

public class C2 : I
{
private C1 c1;

public event MyEventHandler EventName = c1.EventName;

}

How can the above functionality be achieved. I need this functionality
because I am implementing the Model View Presenter pattern as described
on Martin Fowlers webpage, and here it is suggested to use an interface
of the view, to make unit testing of the GUI behaviour possible.

You can't do that, as events are basically sets of methods (add, remove
and potentially raise, although C# doesn't support the last).

In C2, you could implement the event as:

public event MyEventHandler EventName
{
add
{
c1.EventName += value;
}
remove
{
c1.EventName -= value;
}
}

--
Jon Skeet - <sk***@pobox.com>
http://www.pobox.com/~skeet
If replying to the group, please do not mail me too