C# Partial Class & Method

In C#, a partial class is a class that is split into multiple files, allowing the definition of a class to be spread across several physical files. This can be useful in large projects where different developers can work on different parts of the same class without stepping on each other's toes.

To define a partial class, you simply use the partial keyword in front of the class definition. Here's an example:

public partial class MyClass
{
    public void Method1()
    {
        // implementation of Method1
    }
}

public partial class MyClass
{
    public void Method2()
    {
        // implementation of Method2
    }
}

In this example, the class MyClass is defined as a partial class in two different files. The Method1 method is defined in one file, while the Method2 method is defined in another file. Both files are compiled into a single class by the C# compiler.

Partial methods are a special kind of method that is defined in a partial class, but the implementation is optional. This means that you can define a partial method in one part of the class and not provide an implementation for it. The implementation can be added in another part of the class, but it is not required. Partial methods are always private, and the method signature must match in all parts of the class.

Here's an example of a partial class with a partial method:

public partial class MyClass
{
    partial void Method3();

    public void DoSomething()
    {
        // implementation of DoSomething
        Method3();
    }
}

public partial class MyClass
{
    partial void Method3()
    {
        // implementation of Method3
    }
}

In this example, the MyClass class has a Method3 partial method that is defined in one part of the class but implemented in another. The Method3 method is called by the DoSomething method in the first part of the class, but the actual implementation is provided in the second part of the class.

Partial classes and partial methods are useful in large projects where different parts of a class need to be implemented by different developers or where a class is too large to be defined in a single file.