Extending multiple Controls

[Wolfgang Hanke]

Hello,

I want to extend multiple Controls like TextBox, Label, ComboBox etc. with
the same new featureset (for Example all need a Method getSomething())
Because I cant alter their Base-Class I have to write one new class for each
Control like MyTextBox, MyLabel, MyComboBox implementing
IMyControlInter face.
The Code for each Control is exactly the same but C# offers no way to
"include" some code.

Do I really have to write all the code into every Class? Isnt their an
elegant way to achieve this?

Any help greatly appreciated!

Best regards,
Wolfgang Hanke

[=?ISO-8859-1?Q?Lasse_V=E5gs=E6ther_Karlsen?=]

Wolfgang Hanke wrote:

Hello,

I want to extend multiple Controls like TextBox, Label, ComboBox etc.
with the same new featureset (for Example all need a Method getSomething())
Because I cant alter their Base-Class I have to write one new class for
each Control like MyTextBox, MyLabel, MyComboBox implementing
IMyControlInter face.
The Code for each Control is exactly the same but C# offers no way to
"include" some code.

Do I really have to write all the code into every Class? Isnt their an
elegant way to achieve this?

Any help greatly appreciated!

Best regards,
Wolfgang Hanke

If you can put the code into a common method/class you can call, then
you can do that, otherwise no, you need to place the code into each class.

You could do it like this:

1. Create a common class implementing IMyControlInter face
2. Create the new control classes (MyTextBox, etc.)
3. In the new classes, add a member field of type IMyControlInter face
4. In the constructor of the new classes, construct an instance of
the common class and store into the member field
5. Implement IMyControlInter face on the new classes, each method
and/or property would just read/write/call the corresponding
member on the object in the member field

--
Lasse Vågsæther Karlsen
mailto:la***@vk arlsen.no
http://presentationmode.blogspot.com/
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[Marc Gravell]

If the code is the same... would it suffice to just have a method that
accepts Control? Or is it something specific you are doing?

Well, C# 3 extension methods could do what you describe; you'd still
need separate extension methods for each type, but they could all call
into the same implementation:

public static class ControlExt {
public static void DoSomething(thi s Label label)
{DoSomethingImp (label);}
public static void DoSomething(thi s TextBox textBox)
{DoSomethingImp (textBox);}
// etc
static void DoSomethingImp( Control control) {
// your code
}
}

Now against a Lable (for example) you will be able to use:
label1.DoSometh ing();

Marc

[Wolfgang Hanke]

Thank you, I did not know about those extension methods. I will have a
closer look at them even though it sounds as if you should not use them
extensively...

Wolfgang

[Wolfgang Hanke]

You could do it like this:

>
1. Create a common class implementing IMyControlInter face
2. Create the new control classes (MyTextBox, etc.)
3. In the new classes, add a member field of type IMyControlInter face
4. In the constructor of the new classes, construct an instance of
the common class and store into the member field
5. Implement IMyControlInter face on the new classes, each method
and/or property would just read/write/call the corresponding
member on the object in the member field

Yes, those were my thoughts, too. But Delphi offers so called "class
helpers" to extend classes where you dont have access to. So i thought there
could be something similar in C#.
Those Extension Methods mentioned by Marc seem to be the closest equivalent.

Does anyone know a Design Pattern for "extending" a base class in this way?
Dont want to invent a new wheel...

Wolfgang

[Marc Gravell]

Note that extension methods are just compiler trickery to make it *seem*
like there is an instance method (DoSomething) on the nominated control.
In reality they are just static methods that accept the instance as the
first argument, and they need the C# 3 compiler. But it might help...

Marc