Aborting a constructor

[Marc Scheuner [MVP ADSI]]

Folks,

I have a plug-in system where I have a host that creates child forms
to be displayed (in an MDI manner). One requirement is that if certain
conditions apply, a child form should not be created, e.g. I would
have to be able to abort the child's constructor, if I see that
certain things are missing.

How can I do this? I come from Delphi, and we used to have a "silent"
exception called "Abort" there - throw it in the constructor and the
execution of the constructor was stopped right there, and a null
pointer was returned (instead of a created instance) - is there
something similar in C# ? Can't seem to find anything to that
effect.....

Thanks!
Marc

================================================== ==============
Marc Scheuner May The Source Be With You!
Bern, Switzerland m.scheuner(at)inova.ch

[Jon Skeet]

Marc Scheuner [MVP ADSI] <m.********@inova.SPAMBEGONE.ch> wrote:

I have a plug-in system where I have a host that creates child forms
to be displayed (in an MDI manner). One requirement is that if certain
conditions apply, a child form should not be created, e.g. I would
have to be able to abort the child's constructor, if I see that
certain things are missing.

How can I do this? I come from Delphi, and we used to have a "silent"
exception called "Abort" there - throw it in the constructor and the
execution of the constructor was stopped right there, and a null
pointer was returned (instead of a created instance) - is there
something similar in C# ? Can't seem to find anything to that
effect.....

The equivalent is to have a static method which calls a constructor and
either returns the new reference or null if an exception occurs. I for
one am very glad that constructors can't silently return null!

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

[Jay B. Harlow [MVP - Outlook]]

Marc,
To further Jon's comment.

I would considering having the static method return a NullObject instead of
null. Depending on how far & wide the returned object was going to be used.
This avoids checking for null all over your code...

A NullObject is an application of the Special Case pattern.
http://www.martinfowler.com/eaaCatalog/specialCase.html

Hope this helps
Jay

"Marc Scheuner [MVP ADSI]" <m.********@inova.SPAMBEGONE.ch> wrote in message
news:km********************************@4ax.com...

Folks,

I have a plug-in system where I have a host that creates child forms
to be displayed (in an MDI manner). One requirement is that if certain
conditions apply, a child form should not be created, e.g. I would
have to be able to abort the child's constructor, if I see that
certain things are missing.

How can I do this? I come from Delphi, and we used to have a "silent"
exception called "Abort" there - throw it in the constructor and the
execution of the constructor was stopped right there, and a null
pointer was returned (instead of a created instance) - is there
something similar in C# ? Can't seem to find anything to that
effect.....

Thanks!
Marc

================================================== ==============
Marc Scheuner May The Source Be With You!
Bern, Switzerland m.scheuner(at)inova.ch