I want to inherit from Bitmap to add a property but I can't because it's
sealed. Is there any reason to seal a class?
Thanks,
Michael
32  9429 
Michael C schreef:
I want to inherit from Bitmap to add a property but I can't because it's
sealed. Is there any reason to seal a class?
Thanks,
Michael
The main purpose of a sealed class is to take away the inheritance
feature so the user can not derive a class from that particular class.
In this way you can seal the boundaries of your application. Normally
it is done with static classes. Structs are always sealed.
The only thing i can think of in this case is that the Microsoft
programmers didn't want any derivation because the Bitmap class
implements the members declared in the Image class. Perhaps that
overriding them could cause problems in other classes.
I hope that this answer gives you all the information that you want.
Hi,
It's a design decision , it's an indication that there is no further
inheritance expected for that class.
--
--
Ignacio Machin,
ignacio.machin AT dot.state.fl.us
Florida Department Of Transportation
"Michael C" <no****@nospam. comwrote in message
news:en******** *****@TK2MSFTNG P05.phx.gbl...
>I want to inherit from Bitmap to add a property but I can't because it's
sealed. Is there any reason to seal a class?
Thanks,
Michael
"Ignacio Machin ( .NET/ C# MVP )" <ignacio.mach in AT dot.state.fl.us wrote
in message news:OK******** ******@TK2MSFTN GP05.phx.gbl...
Hi,
It's a design decision , it's an indication that there is no further
inheritance expected for that class.
It's a pity, I just want to add some fairly harmless properties like a Tag
property so I can pass some extra info around with the bitmap. It seams to
me that if inheriting the bitmap could cause problems if certain method are
overridden isn't really that big a deal. We can cause all sorts of problems
using the api but we still get to go that :-)
Michael
There are other way rather than inheritance, for example you can use
aggregation -realizing you own custom Bitmap class and using it everywhere
--
WBR,
Michael Nemtsev :: blog: http://spaces.msn.com/laflour
"At times one remains faithful to a cause only because its opponents do not
cease to be insipid." (c) Friedrich Nietzsche
"Michael C" wrote:
"Ignacio Machin ( .NET/ C# MVP )" <ignacio.mach in AT dot.state.fl.us wrote
in message news:OK******** ******@TK2MSFTN GP05.phx.gbl...
Hi,
It's a design decision , it's an indication that there is no further
inheritance expected for that class.
It's a pity, I just want to add some fairly harmless properties like a Tag
property so I can pass some extra info around with the bitmap. It seams to
me that if inheriting the bitmap could cause problems if certain method are
overridden isn't really that big a deal. We can cause all sorts of problems
using the api but we still get to go that :-)
Michael
"Michael C" <no****@nospam. comwrote in
news:el******** ******@TK2MSFTN GP05.phx.gbl:
It's a pity, I just want to add some fairly harmless properties like a
Tag property so I can pass some extra info around with the bitmap. It
seams to me that if inheriting the bitmap could cause problems if
certain method are overridden isn't really that big a deal. We can
cause all sorts of problems using the api but we still get to go that
While I agree with you in principle and in practice, I can offer the
(obvious?) suggestion to write a class that has a Bitmap as a member, plus
whatever other properties you want to pass around. Then use an instance of
that class in place of Bitmap, and reference the bitmap member when you
want to use the bitmap itself.
-mdb
"Michael Bray" <mbray@makeDInt oDot_ctiusaDcom wrote in message
news:Xn******** *************** ***@207.46.248. 16...
While I agree with you in principle and in practice, I can offer the
(obvious?) suggestion to write a class that has a Bitmap as a member, plus
whatever other properties you want to pass around. Then use an instance
of
that class in place of Bitmap, and reference the bitmap member when you
want to use the bitmap itself.
That makes sense and is possibly a better solution. What I'm doing is faking
16 bit grayscale bitmaps by using two 8 bit bitmaps as the high and low
order bits. I was hoping to make the low order bitmap a property of the high
order bitmap so that I can can have functions that accept a bitmap as a
parameter check for the low order bitmap.
Michael
Hi Michael,
In .NET 3.0 (shipping with Windows Vista, so I've heard) there are Extender
methods so you can decorate instances of any object or interface with your
own methods and their implementations .
I just thought you might find that interesting. You can download the LINQ
preview for VS.NET 2005 and play around with the up-and-coming functionality
yourself.
I wish it was available for production already 'cause I could sure use LINQ
now. http://msdn.microsoft.com/data/ref/linq/
- Dave Sexton
"Michael C" <no****@nospam. comwrote in message
news:el******** ********@TK2MSF TNGP05.phx.gbl. ..
"Ignacio Machin ( .NET/ C# MVP )" <ignacio.mach in AT dot.state.fl.us >
wrote in message news:OK******** ******@TK2MSFTN GP05.phx.gbl...
>Hi,
It's a design decision , it's an indication that there is no further
inheritance expected for that class.
It's a pity, I just want to add some fairly harmless properties like a Tag
property so I can pass some extra info around with the bitmap. It seams to
me that if inheriting the bitmap could cause problems if certain method
are overridden isn't really that big a deal. We can cause all sorts of
problems using the api but we still get to go that :-)
Michael
Michael C wrote:
I want to inherit from Bitmap to add a property but I can't because it's
sealed. Is there any reason to seal a class?
Supporting the possibility of inheritance--in a published interface
like the .NET Framework--is a lot of work. You have to design your
class's public and protected members with inheritance in mind, ensuring
that anyone inheriting from the class can insert functionality at
useful points, and ensuring that it's reasonably hard to do stupid
things and jackpot one's self while inheriting.
As well, usually, you expose more about the internal workings of your
class and therefore make it more difficult to change in the future,
because the class's contract with the "public" (which now includes
public users and protected inheritors) is stronger.
An example of a badly designed class that supports inheritance is
PrintPreviewDia log, which allows inheritance but has almost every
behaviour / appearance element you could possibly want to modify in a
child class secured as "private". Some writers prefer to simply seal
the class rather than release nonsense like this.
Hello Dave,
Take into account that .NET 3.0 is just .NET 2.0 + WinFX, there is no .net
3.0 framework at all.
..net 3.0 is just marketing and nothing else
DSIn .NET 3.0 (shipping with Windows Vista, so I've heard) there are
DSExtender methods so you can decorate instances of any object or
DSinterface with your own methods and their implementations .
DS>
DSI just thought you might find that interesting. You can download
DSthe LINQ preview for VS.NET 2005 and play around with the
DSup-and-coming functionality yourself.
DS>
DSI wish it was available for production already 'cause I could sure
DSuse LINQ now.
DS>
DS http://msdn.microsoft.com/data/ref/linq/
DS>
DS- Dave Sexton
DS>
DS"Michael C" <no****@nospam. comwrote in message
DSnews:el****** **********@TK2M SFTNGP05.phx.gb l...
DS>
>"Ignacio Machin ( .NET/ C# MVP )" <ignacio.mach in AT dot.state.fl.us >
wrote in message news:OK******** ******@TK2MSFTN GP05.phx.gbl...
>>Hi,
It's a design decision , it's an indication that there is no further
inheritance expected for that class.
It's a pity, I just want to add some fairly harmless properties like
a Tag property so I can pass some extra info around with the bitmap.
It seams to me that if inheriting the bitmap could cause problems if
certain method are overridden isn't really that big a deal. We can
cause all sorts of problems using the api but we still get to go that
:-)
Michael
---
WBR,
Michael Nemtsev :: blog: http://spaces.msn.com/laflour
"At times one remains faithful to a cause only because its opponents do not
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