C# Discussion Boards - CodeProject

Image disposeOfSoon = pictureBox.Image;<br />
using (disposeOfSoon)<br />
{<br />
   // use disposeOfSoon <br />
   pictureBox.Image = newImage; <br />
}   // compiler will call Dispose on disposeOfSoon

"When the only tool you have is a hammer, a sore thumb you will have."

I'm not sure if that works, but if it does, its totally ludicrous!!!

1. IMO the variable shouldnt leave the using block.
2. No object was created, only referenced.

leppie ::AllocCPArticle("Zee blog");
Seen on my Campus BBS: Linux is free...coz no-one wants to pay for it.

I have to be honest that I could not see the point myself with the original code. So I guessed its not real and just an example.

in terms of your points:
1. the variable does not leave the using block...
2. calling dispose on an object which is pointing at a image works, as all you are doing is asking the image object to call dispose - which is worth doing if you don't want it anymore.

hope this makes sense, or else I've misunderstood your points Frown | :(

"When the only tool you have is a hammer, a sore thumb you will have."

The code is real, it describes a common situation: a picture box displays an image for some unspecified duration, then in response to some event the image should change. AFAIK this requires the soon-to-be-old current image be pointed to, the new image be displayed, and the now-old-current image be disposed. Surely this is a common problem. Nes pas?

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Gosh, it would be awful pleas'n, to reason out the reason, for things I can't explain.
Then perhaps I'd deserve ya, and be even worthy of ya..
if I only had a brain!

Philip Fitzsimons wrote:
the variable does not leave the using block...

What I meant to say was the variable was enclosed, iow declared too. Thus the compiler can pickup a problem readily.

Philip Fitzsimons wrote:
calling dispose on an object which is pointing at a image works, as all you are doing is asking the image object to call dispose - which is worth doing if you don't want it anymore.

Its all and well, but not if it someone elses object that mite need to exist after the method returns. Refer to above. IMO the object should be sandboxed in the scope.

leppie ::AllocCPArticle("Zee blog");
Seen on my Campus BBS: Linux is free...coz no-one wants to pay for it.

i agree in principle with what you're saying, that's why i wrote the post. the problem is that there isn't any good local "scope" for the image, once the pictureBox gets it it should belong to the pictureBox. perhaps i should write PictureBoxEx.. (yecch!!)

btw the snippet provided by Philip Fitzsimons "looks" kinda wierd but works great! if we could get EricGu to rename the keyword "using" to "noLongerUsing" the snippet would read:

Image tmp;
noLongerUsing (tmp = pictureBox.Image)
{pictureBox.Image = aBrandNewImage;}
Smile | :)

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Gosh, it would be awful pleas'n, to reason out the reason, for things I can't explain.
Then perhaps I'd deserve ya, and be even worthy of ya..
if I only had a brain!

what are the design tradeoffs between different constructs to collect objects based on some common functionality?

Suppose i want to rely on objects being able to "display" themselves. What's the difference between using Abstract Base, Interface, or Attribute? Since c# doesnt allow multiple inheritance i'd guess Abstract base should be reserved for "core" properties of the object, and i guess Interfaces are there exactly so my displayThyself methods can be expressed. What about [Serializable], that has properties similar to an interface except for specifying a constructor as one of the mandatory methods.

Is there a discussion of what construct to use when and why?

Thanks in advance! Smile | :)

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Gosh, it would be awful pleas'n, to reason out the reason, for things I can't explain.
Then perhaps I'd deserve ya, and be even worthy of ya..
if I only had a brain!

TuringTest1 wrote:
i'd guess Abstract base should be reserved for "core" properties of the object

Yes.

TuringTest1 wrote:
i guess Interfaces are there exactly so my displayThyself methods can be expressed.

Well,you mention that multiple inheritance is not allowed in C#,with Interfaces you can have multiple inheritane,you inherit a class from another class AND how many interface you want.

Serializable word express itself.It means you can seriallize this class. MSDN exapain these things very good,you can start from it.

Mazy

No sig. available now.

Mazdak wrote:
Serializable word express itself.It means you can seriallize this class. MSDN exapain these things very good,you can start from it.

yes, [Serializable] is implemented as an attribute, but it really looks like an Interface, doesn't it? except that for technical reasons (one of the 2 interface "methods" is a constructor) it can't be an interface. Or something like that. What are the similarities and differences between something implemented as an Interface and something like [Serializable] which is implemented via attributes?

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Gosh, it would be awful pleas'n, to reason out the reason, for things I can't explain.
Then perhaps I'd deserve ya, and be even worthy of ya..
if I only had a brain!

Actually, if you attribute your class with the SerializableAttribute, the default serialization will serialize public and private fields of your class. There is an interface, ISerializable, that allows you to control the serialization so that you, the developer, controls what gets serialized and what doesn't. This does go along - like the original poster mentioned - with a constructor that has the signature (SerializationInfo, StreamingContext). This constructor can have any access modifier, but are common protected so that subclasses can pass serialization info to its base class.

There are also other serialization interfaces that can be useful, such as the IDeserializationCallback that allows you to perform any layout or hook-ups after serialization is complete, and the ISerializationSurrogate that - with an IFormatter implementation allows you to serialize Types that are themselves serializable. You can also use a SerializationBinder with the formatter to serialize from one Type to another, using SerializationBinder.BindToType. This seems especially handy when you have to upgrade a serialized file with older versions of Types.

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So marking class Foo with [Serializable] magically adds expands Foo by implemnting the 2 ISerializable methods ending up with Foo : ISerializable?

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Gosh, it would be awful pleas'n, to reason out the reason, for things I can't explain.
Then perhaps I'd deserve ya, and be even worthy of ya..
if I only had a brain!

No, you still have to implement ISerializable if you wish. Just attributing the class as I mentioned before with SerializableAttribute serializes all private and public fields. Implementing ISerializable is required if you want to control what gets serialized. See the ISerializable documentation for both more detail and an example.

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Heath Stewart wrote:
Actually, if you attribute your class with the SerializableAttribute, the default serialization will serialize public and private fields of your class.

how does this happen? doesnt it require "somebody" to implement a default ISerializable for the class? or is it just done at runtime via reflection? [[need more smiley flavors for "huh??"!!!)

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Gosh, it would be awful pleas'n, to reason out the reason, for things I can't explain.
Then perhaps I'd deserve ya, and be even worthy of ya..
if I only had a brain!

If you'll read the documentation for SerializableAttribute, you'll see that the serialization infrastructure serializes private and public fields by default if a class is attributed (the class itself - inheriting the attribute doesn't make a derivative class serializable). This is done via reflection, yes. Note that your class must be attributed with the SerializableAttribute even if it implements ISerializable to be serializable. Implementing the interface just gives you explicit control over serialization of your Type.

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GCS/G/MU d- s: a- C++++ UL@ P++(+++) L+(--) E--- W+++ N++ o+ K? w++++ O- M(+) V? PS-- PE Y++ PGP++ t++@ 5 X+++ R+@ tv+ b(-)>b++ DI++++ D+ G e++>+++ h---* r+++ y+++
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ok, i guess i see how this is done-- pls correct me if i'm wrong: on invoking Formatter.Serialize, Formatter uses reflection to check whether ISerializable is implemented in the class of the object. if so it calls the interface. If not it uses reflection to serialize all the fields, checking for the NonSerialized as it goes.

is that what happens? and if this is, how is that done efficiently enough to not take forever to serialize each two-bit-- i mean two-byte-- object in the graph? does BinaryFormatter perform some sort of run time analysis or "compilation" like regex?

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Gosh, it would be awful pleas'n, to reason out the reason, for things I can't explain.
Then perhaps I'd deserve ya, and be even worthy of ya..
if I only had a brain!

You should read Serializing Objects[^] in the .NET Framework. I think it'll help understand many of these concepts.

As far as performance, it is true that reflecting all those fields and Types takes a while but it is necessary when crossing contexts (via Remoting) or serialing to streams for any other means. The process of serialization is actually pretty complex. If you're interested in the details, you should use ildasm.exe (if you know IL) or a good decompiler like .NET Reflector[^] to see how much of that is done.

Our application I designed uses A LOT of Remoting in the Internet-deployed edition and it functions pretty fast - not much slower than the LAN version (and most people don't even notice). As far as I can tell, nothing is cached from serialization to serialization either because everything changes from call to call.

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thanks, yes i also use BinaryFormatter on pretty big objects and it seems remarkably efficient. Thanks for the suggestion on Reflector (do i also need to learn il?).

Thanks for the insights and the Reflector fishing rod!! Big Grin | :-D

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Gosh, it would be awful pleas'n, to reason out the reason, for things I can't explain.
Then perhaps I'd deserve ya, and be even worthy of ya..
if I only had a brain!

Why not learn IL? You can never know too much. Besides, decompilers don't always do such a great job so you'll have to look at IL at some point to see what's really going on. At least knowing what the instructions do is important, which is also documented in the .NET Framework SDK.

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yikes! i guess you're right, that probably is the key to a lot of things i wish i knew how they were implemented, but i must admit it sounds fairly daunting!!

also brings up a dumb question, is it obvious that the inner loop of the serialization (in BinaryFormatter?) would likely be written in IL not native x86?

Thx!

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Gosh, it would be awful pleas'n, to reason out the reason, for things I can't explain.
Then perhaps I'd deserve ya, and be even worthy of ya..
if I only had a brain!

All compilers targeting the CLR using pure managed code produce Intermediate Language, or IL. So yes, it is IL. In fact, the Managed C++ compiler is the only compiler publicly available from Microsoft that can produce native code in an assembly (known as mixed mode).

But using an loop for serialization would be a poor idea. Recursion is most likely at work since for every Type that is added to the SerializationInfo, it has to be serialized, and then their Types, and so on so forth.

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By decorating your class with the Serializable attribute you are just telling other classes that you pass it to that it is "auto-serializable", by which it is meant that it contains no volatile references (i.e. a SQLConnection object) or references to other classes that are not serializable. This way a remoting object (for example) knows that it does not need any special instructions to serialize/deserialize.

DTrent

i hadn't thought about the volatile references, thanks!

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Gosh, it would be awful pleas'n, to reason out the reason, for things I can't explain.
Then perhaps I'd deserve ya, and be even worthy of ya..
if I only had a brain!

I was working on POP3 mail application. I'm able to implement the POP3 protocol and get the mails and attachments.. etc. But i'm unable to decode some of the mails encoded by Quoted-Printable Content-Transfer-Encoding.
Please help ASAP.

If you're looking for the rules for decoding quoted-printable encodings, see RFC 1521: http://www.ietf.org/rfc/rfc1521.txt, section 5.1.

When you say you're unable to decode, is there some specific problem or are you just having problems with the rules required for decoding? The link above should help.

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Thanks Heath for your reply. But....
I needed the code in C# for decoding Quoted-Printable text.