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Extension Methods with Custom Classes

I'm attempting to extend my custom classes and running into a problem where it cannot find the extension method.. I have and can extend any built in classes or even ones contained within DLL's. I don't know if this is a compilation error or if I'm doing something wrong. Threw together a small program for an example, won't compile..
Here's the extension:
namespace ExtensionMethodTesting.Extension
{
public static class Extension
{
public static void DoSomething(this ExtensionMethodTesting.Blah.CustomClass r)
{
}
}
}
Here's the Custom Class:
namespace ExtensionMethodTesting.Blah
{
public class CustomClass
{
public static void DoNothing()
{
}
}
}
Here's the code calling it:
using ExtensionMethodTesting.Blah;
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using ExtensionMethodTesting.Extension;
namespace ExtensionMethodTesting
{
class Program
{
static void Main(string[] args)
{
CustomClass.DoNothing();
CustomClass.DoSomething();
}
}
}
I must be missing something... Anyways the exact error just for clarification is:
Error 1 'ExtensionMethodTesting.Blah.CustomClass' does not contain a definition for 'DoSomething' c:\users\damon\documents\visual studio 2013\Projects\ExtensionMethodTesting\ExtensionMethodTesting\Program.cs 16 25 ExtensionMethodTesting

Extension methods require an instance of an object. You'll have to new up a CustomClass to use it.
var custom = new CustomClass();
custom.DoSomething();
See this answer as to why that is.

You need to instantiate an object of the CustomClass to use its extension method.
CustomClass obj = new CustomClass();
obj.DoSomething();

Namespace issue with period

I have a class:
namespace FooIOS
{
public class Foo
{
public static void doThis() {...}
}
}
And this works:
using FooIOS;
namespace Sample.iOS
{
public void method () {
Foo.doThis();
}
}
However, this does not work the same way when I change the namespace to insert a period:
namespace Foo.iOS
{
public class Foo
{
public static void doThis() {...}
}
}
using Foo.iOS;
namespace Sample.iOS
{
public void method () {
// Compilation error
Foo.doThis();
// Compilation error
Foo.iOS.doThis()
// This works but I can't have it that long and complicated (I'm writing an API call)
Foo.iOS.Foo.doThis();
}
}
I'm pretty inexperienced with C# and I'm wondering if there's any way to use the period in the namespace and not deal with the complicated call.

namespace Foo.iOS
{
public class Foo
{
public static void doThis() {...}
}
}
Your namespace name is Foo.iOS, class name is Foo, static method name is doThis(). The fully qualified path to access that method is NAMESPACE.CLASS.METHOD_NAME, so it becomes:
Foo.iOS.Foo.doThis();
Here is nothing wrong with C#, but with the naming you use.
From this a couple of suggestions:
try to no use . inside names of the namespace, as this introduces confusion
try to not name namespace as the class inside it, as this introduces confusion.
I'm pretty inexperienced with C# and I'm wondering if there's any way
to use the period in the namespace and not deal with the complicated
call.
Short answer is: name your namespaces, classes and member functions in a way, that it does not look complicated to you and to others.
EDIT
Consider that you can use also Namespace Alias.
For example:
using IOS = Foo.iOS;
...
IOS.Foo.doThis();
But as I said before, it's better to avoid . in namespace name at first place.

Bring the using Foo.iOS; statement inside the namespace Sample.iOS namespace block, like shown below, then you will be able to call doThis() like in your 1st attempt Foo.doThis(); that was previously giving you a compile error.
namespace Sample.iOS
{
using Foo.iOS;
public void method () {
// this works
Foo.doThis();
}
}
Related reading: Inside or Outside? by Eric Lippert on MSDN.
Fully working Code sample:
Create a new Console App in Visual Studio, and then in the Program.cs class, delete all lines, paste the following, do a compile and then run.
using System;
namespace Foo.iOS
{
public class Foo
{
public static void doThis() { Console.Write("Inside doThis");}
}
}
namespace Sample.iOS
{
using Foo.iOS;
class Program
{
static void Main(string[] args)
{
method();
Console.ReadKey();
}
public static void method ()
{
// works fine
Foo.doThis();
}
}
}

Equivalent to Java's "restricted" and "extends" in C#?

EDIT: I apologize, I meant protected instead of restricted. I was tired.
Is there an equivalent to Java's restricted and extends in C#? I can see that neither are in C#, and they would be useful for a current programming project.
Code:
using System;
namespace CServer.API
{
public class Plugin
{
restricted Plugin ()
{
}
}
}
and say a plugin did this:
using System;
using CServer.API;
namespace Whatever
{
public class WhateverPlugin extends Plugin
{
}
}
I want to have a custom constructor that executes some code before the plugin's constructor.

It sounds like you probably want:
using System;
namespace CServer.API
{
public class Plugin
{
protected Plugin()
{
// This code will execute before the body of the constructor
// in WhateverPlugin
}
}
}
and
using System;
using CServer.API;
namespace Whatever
{
// : is broadly equivalent to both implements and extends
public class WhateverPlugin : Plugin
{
public WhateverPlugin() // implicitly calls base constructor
{
// This will execute after the Plugin constructor body
}
}
}
Note that restricted isn't a keyword in Java; I'm assuming you actually mean protected.

Class structure confirmation

I have this class file call SMSHelper.cs First I just wanted to know is my written structure is Correct or Wrong?(My class file name is also SMSHelper.cs & my first class also SMSHelper here you can see in the code.).
Basically I have 3 classes in same file. One class has the same name as the file name.
using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Text;
using System.Text.RegularExpressions;
namespace SMSBase.SMSFunction
{
public class SMSHelper : DotNetNuke.Entities.Modules.PortalModuleBase
{
// Some Code here
// Return Something here
}
public class Validator
{
public bool IsValidate(string Item)
{
// Some Code Here Not return anything
}
public class HuntingDate
{
//Implementation & Constructor here.. Return Something
}
}
}

There is nothing wrong in your class structure (except one missing bracket). And there is no matter your class name and file name are same. You can access and initialize your class objects like that...
SMSBase.SMSFunction.SMSHelper objSMSHelper = new SMSBase.SMSFunction.SMSHelper();
SMSBase.SMSFunction.Validator objValidator = new SMSBase.SMSFunction.Validator();
SMSBase.SMSFunction.HuntingDate objHuntingDate = new SMSBase.SMSFunction.HuntingDate();
This SMSBase.SMSFunction is your namespace... you can access classes by your namespace or include this namespace in the class header like
using SMSBase.SMSFunction

There is a problem in opening closing brackets:
namespace SMSBase.SMSFunction
{
public class SMSHelper : DotNetNuke.Entities.Modules.PortalModuleBase
{ // Some Code here // Return Something here
}
public class Validator
{
public bool IsValidate(string Item)
{ // Some Code Here Not return anything
}
}
public class HuntingDate
{ //Implementation & Constructor here.. Return Something
}
}
If that is what you are asking.

Yes as Talha ,said one bracket is missing.Try to put that.
When we want to call the class name its better to call with "namespace.ClassName" format which gives clarity to the compiler.

Why do extension methods not work with namespace aliasing?

This may be an ignorant question, but I'm unsure why I can not use namespace aliasing and extension methods together.
The following example works just fine:
Program.cs
using System;
using ExtensionMethodTest.Domain;
namespace ExtensionMethodTest
{
class Program
{
static void Main(string[] args)
{
var m = new Domain.MyClass();
var result = m.UpperCaseName();
}
}
}
MyClass.cs
using System;
namespace ExtensionMethodTest.Domain
{
public class MyClass
{
public string Name { get; set; }
}
}
MyClassExtensions.cs
using System;
namespace ExtensionMethodTest.Domain
{
public static class MyClassExtensions
{
public static string UpperCaseName (this MyClass myClass)
{
return myClass.Name.ToUpper();
}
}
}
However, when I alias domain as follows in Program.cs:
using Domain = ExtensionMethodTest.Domain;
The extension method no longer works..
This can be rather frustrating when I'm dealing with converting various domain objects to contract objects (let's say I have 4 domain assemblies and 4 contract assemblies) for use in a web service. Using aliasing would be very handy as I could alias as follows and continue to use the various extension methods (such as ToContract, etc.):
using BillingContracts = Namespace.Billing.Contracts;
using IssuingContracts = Namespace.Issuing.Contracts;
etc...
I look forward to the answer.. I'm sure it's straight forward, but I, for the life of me, can't figure out why it doesn't work.
Thanks!

Make sure to still add a non-aliased using statement:
Program.cs
using System;
using ExtensionMethodTest.Domain; //DON'T FORGET A NON-ALIASED USING
using MyDomain = ExtensionMethodTest.Domain;
namespace ExtensionMethodTest
{
class Program
{
static void Main(string[] args)
{
var m = new MyDomain.MyClass();
var result = m.UpperCaseName();
}
}
}
MyClass.cs
using System;
namespace ExtensionMethodTest.Domain
{
public class MyClass
{
public string Name { get; set; }
}
}
MyClassExtensions.cs
using System;
namespace ExtensionMethodTest.Domain
{
public static class MyClassExtensions
{
public static string UpperCaseName (this MyClass myClass)
{
return myClass.Name.ToUpper();
}
}
}

I also love to use namespace aliasing but its not working in case of Extension methods. So one thing that i did is, I changed the namespace of extension class to same namespace that my main project has (although my extension class resides in sub folder of main project).
Suppose I have a project myFirstProj which surely has namespace myFirstProj for root classes. My extension class is present in myFirstProj/Common/myExtensionClass with contains namespace myFirstProj.Common { //myExtensionClass }.
So now what I did is, I changed the namespace of myExtensionClass from namespace myFirstProj.Common{ //myExtensionClass } to namespace myFirstProj{ //myExtensionClass } .
Now i can use my extension methods in my whole project myFirstProj event without specifying using statement for my extension class.
I know this isn't a standard way to that but I haven't found any other workaround for it expect this one because for my Project there is a requirement to go with namespace aliasing for project namespaces.