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  Partial classes

Partial classes provide an ability to split class declaration (usually into separate files). A common problem that can be solved with partial classes is allowing users to modify auto-generated code without fearing that their changes will be overwritten if the code is regenerated. Also multiple developers can work on same class or methods.

using System;

namespace PartialClassAndMethods
{
    public partial class PartialClass
    {
        public void ExampleMethod() {
            Console.WriteLine("Method call from the first declaration.");
        }
    }

    public partial class PartialClass
    {
        public void AnotherExampleMethod()
        {
            Console.WriteLine("Method call from the second declaration.");
        }
    }

    class Program
    {
        static void Main(string[] args)
        {
            PartialClass partial = new PartialClass();
            partial.ExampleMethod(); // outputs "Method call from the first declaration."
            partial.AnotherExampleMethod(); // outputs "Method call from the second declaration."
        }
    }
}
  Partial methods

Partial method consists of the definition in one partial class declaration (as a common scenario - in the auto-generated one) and the implementation in another partial class declaration.

using System;

namespace PartialClassAndMethods
{
    public partial class PartialClass // Auto-generated
    {
        partial void PartialMethod();
    }

    public partial class PartialClass // Human-written
    {
        public void PartialMethod()
        {
            Console.WriteLine("Partial method called.");
        }
    }

    class Program
    {
        static void Main(string[] args)
        {
            PartialClass partial = new PartialClass();
            partial.PartialMethod(); // outputs "Partial method called."
        }
    }
}
  Partial classes inheriting from a base class

When inheriting from any base class, only one partial class needs to have the base class specified.

// PartialClass1.cs
public partial class PartialClass : BaseClass {}

// PartialClass2.cs
public partial class PartialClass {}

You can specify the same base class in more than one partial class. It will get flagged as redundant by some IDE tools, but it does compile correctly.

// PartialClass1.cs
public partial class PartialClass : BaseClass {}

// PartialClass2.cs
public partial class PartialClass : BaseClass {} // base class here is redundant

You cannot specify different base classes in multiple partial classes, it will result in a compiler error.

// PartialClass1.cs
public partial class PartialClass : BaseClass {} // compiler error

// PartialClass2.cs
public partial class PartialClass : OtherBaseClass {} // compiler error

Syntax

  • public partial class MyPartialClass { }

Remarks

  • Partial classes must be defined within the same assembly, and namespace, as the class that they are extending.
  • All parts of the class must use the `partial` keyword.
  • All parts of the class must have the same accessibility; `public`/`protected`/`private` etc..
  • If any part uses the `abstract` keyword, then the combined type is considered abstract.
  • If any part uses the `sealed` keyword, then the combined type is considered sealed.
  • If any part uses the a base type, then the combined type inherits from that type.
  • The combined type inherits all the interfaces defined on all the partial classes. 

    • Read Article
    https://develop.horje.com/learn/1434/reference

     

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