Consider we create a partial class in Project1 and we have a Project2 that has reference to Project1 .How is it possible to declare some other method of partial class in Project2 ?
thanks
The partial construct is only a compiler functionality, to allow a class to be spread out in several source files. The compiled class still lives in one and only one class library (dll file).
There are two ways to extend a class in another library:
Inheritance, unless the class is sealed. This requires that the calling code handles all object instantiation to instantiate the new derived class.
Extension methods, which makes the code look like there are new methods on that class, but that is just syntactic sugar. It won't change the class itself.
It is not possible to extend a partial class in another project. Partial is only compiler sugar. The compiler will create only one class in the resulting assembly.
You can use the Extension methods that allow you to create additional methods for existing class
Partial classes cannot exist out side assembly boundaries!
Related
I am trying to clean up all designer errors in our solutions and ran into the following error:
The designer could not be shown for this file because none of the classes within it can be designed. The designer inspected the following classes in the file: DoubleAttributeTextBoxBase --- The base class 'NumericAttributeTextBoxBase' could not be loaded. Ensure the assembly has been referenced and that all projects have been built.
The classes are both defined in the same assembly so I know it's not a reference problem. I'm wondering if it has anything to do with the fact that the base class is generic. Any ideas?
public class DoubleAttributeTextBoxBase : NumericAttributeTextBoxBase<double>
public class NumericAttributeTextBoxBase<T> : TextBox where T : IComparable, IComparable<T>
The base class for a class being designed must be non-abstract and non-generic. To make a class that inherits from a generic class designable. The workaround is to insert a trivial non-generic class in-between:
public partial class DoubleAttributeTextBoxBase
: NumericAttributeTextBoxBaseOfDouble
{
public DoubleAttributeTextBoxBase()
{
InitializeComponent();
}
// Now DoubleAttributeTextBoxBase is designable.
}
public class NumericAttributeTextBoxBaseOfDouble
: NumericAttributeTextBoxBase<double>
{
}
To make this as simple as possible, you can even put the non-generic class in the same file as the class you want to design. Just make sure to put it after the class (as I have done above) because the designer expects the first class in the file to be the one being designed.
I don't know of a solution, this has been a severe limitation of Visual studio since C# 2.0 came out. The only thing I can say is to add that control to the page at runtime, then at least you can have your designer back for everything else.
from msdn:
Your component or control cannot be a generic type, which is also called a template type or a parameterized type. The design environment does not support generic types.
http://msdn.microsoft.com/en-us/library/ms171843.aspx
Any ideas of how make internal a base class having a child class of that class public in c#?
In code:
internal class Base { }
public class Child : Base {}
I have a layered architecture and need to expose to other layers (others assemblies) the Child class but not the Base class. I'm using inherit as a way to avoid class composition and all the voile part associated with it.
Any ideas of how to manage this kind of problem?
This cannot be done. You can hide the class by encapsulation, wrapping it and hiding it as implementation.
Base types will always be known.
Instead of making the class internal, you can make all members internal instead. If you do not want Base to be inherited by other assemblies, declare Base's constructor as internal.
This is known C# limitation, however, this is not CLR limitation.
Not the best solution, but it's possible to define new public class which inherits from internal class, using intermediate language.
Also, there might be some languages which already allow you to do this, so there is a chance you don't really need to write IL.
Though, at this point, I don't understand the necessity of Base. Since it's internal, it can't be consumed by others, and polymorpishm is essentially broken. Code reuse with subclassing, but without polymorpishm does not sound good.
Thugh, as I said, imh it is possibe to create a "public" class from "internal class" using IL, after that, yu will be able to consume that "public" class in C# side, eg
public class MyDervClass : MyILPublicClass{}
I've declared a partial class with name "BusinessLayer" in BL namespace, but now I want to add another class with same name, and with keyword "partial" in that namespace. But Whenever I try to add class with with name "BusinessLayer", I'm getting an error, saying I can't declared multiple classes with same name in a namespace. Then how can I use partial classes in a single namespace?
I would fix your code if you'd write some, even just as an example.
Anyway, you should tag both as "partial".
Any declaration of this class, anywhere, should have the "partial" keyword in order to allow it to compile properly.
All declarations of the class must have the partial keyword, otherwise they will be interpreted as different classes and being in the same namespace will cause a compile time error.
My best guess is you're missing a partial keyword somewhere.
Edit: By the way, partial classes can only be declared in the same assembly, iirc. So all parts of the partial class need to be in the same assembly.
How can i create a partial class at runtime?
Example: I have a class
public partial class A
{
}
I want to create partial of my A class at runtime from an XML file.
because I don't compile my project when any change in code.
I know this is little meaning less but i need this.
XOML files work for me?
The point of partial classes is to be able to define parts of it in different source files. In the end, after compilation, what you have is a regular class, indistinguishable of any other. So there is not such a thing as "instantiating a partial class".
The partial keyword is used to separate a class across multiple code files. The compiler merges them together into a single class.
MSDN: Partial Class Definitions
You can't.
A partial class doesn't exist in the CLR. It's more of a Visual Vtudio trick than anything else.
How can I apply an Interface to a form class
partial class Form1 : Form, InterfaceA
Is this correct?
Basically I would like to implement an Interface on a form.
How To ....
A Form is just a class (that subclasses System.Windows.Forms.Form), so yes - standard syntax is fine, as you have it.
Edit: As to your partial class part of the question, no, you need only declare that you implement the interface once. From MSDN...
If any of the parts are declared abstract, then the entire type is considered abstract. If any of the parts are declared sealed, then the entire type is considered sealed. If any of the parts declare a base type, then the entire type inherits that class.
Remember, there's no magic in forms or partial classes. C#/.Net is one of the few Microsoft projects that's wizardry free - it really does tend to behave the way you think it should.
Yes - a form is just a class at the end of the day
When working with partial classes in C#, either:
any declaration with the ':' operator must specify exactly the same baseclass and interfaces
specifying baseclass and interfaces on one of the declarations will suffice
To make life easier for yourself, add the interface specs in only one place (without checking I suspect this is in the designer class part by default when working with the WinForms designer).