Add method to a class from another project

Question

Is it possible to add a method to a class from another project?

I have a class:

namespace ProjectLibrary
{
    public class ClassA
    {
        // some methods
    }
}

I want to add a method to save my object in a file, but I don't want to add this method in my project ProjectLibrary because I don't want to add reference to System.IO (I want to use this project for android application and PC application).

Is there a possibility to add a method SaveToFile() usable only in another project? Or create an abstract method in ClassA but define it in other project.

Like this :

using ProjectLibrary;
namespace ProjectOnPC
{
    void methodExample()
    {
        ClassA obj = new ClassA();
        // do something
        obj.SaveToFile();// => available only in namespace ProjectOnPC
    }
}

Thank you for help

Your declaration `public ClassA` is not valid C#. But as the other comments say, inheritance and extension method are good options -- or even just a method that takes ClassA as a parameter. (Which is all an extension method boils down to anyway.) — Petter Hesselberg, Nov 25 '16 at 10:23

score 3 · Answer 1 · answered Nov 25 '16 at 10:23

3

You can use extension methods.

Example:

namespace ProjectOnPC
{
    public static void SaveToFile(this Class myClass)
    {
      //Save to file.
    }
}

answered Nov 25 '16 at 10:23

Carra

17,808
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You missed the class declaration. – Mitulát báti Nov 25 '16 at 12:57

score 2 · Accepted Answer · edited May 23 '17 at 12:13

The thing You are looking for is called Extension method:

Code for base class:

namespace ProjectLibrary
{
    public ClassA
    {
        // some methods
    }
}

Extension method:

using ProjectLibrary;
namespace ProjectOnPC
{
    void SaveToFile(this ClassA Obj, string Path)
    {
        //Implementation of saving Obj to Path
    }
}

Calling in Your program:

using ProjectLibrary;
using ProjectOnPc; //if You won't include this, You cannot use ext. method

public void Main(string[] args)
{
    ClassA mObj = new ClassA();
    mObj.SaveToFile("c:\\MyFile.xml");
}

Didn,'t know that, thank you for answer and documentation. – A.Pissicat Nov 25 '16 at 10:28 — A.Pissicat, Nov 25 '16 at 10:28

Mitulát báti · Answer 3 · 2016-11-25T12:54:58.520

You can create an extension method for this purpose.

Here's an example.
In your ProjectOnPc namespace create a class like this:

public static class ClassAExtension
{
    public static void SaveToFile(this ClassA obj)
    {
        // write your saving logic here.
        // obj will represent your current instance of ClassA on which you're invoking the method.
        SaveObject(obj).
    }
}

You can learn more about extension methods here:
https://msdn.microsoft.com/en-us//library/bb383977.aspx

Add method to a class from another project

3 Answers3

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