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Split partial classes into separate files

I have a very basic question. In a Visual Studio project, I found two partial classes named Startup. The classes are in different files.

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If I click on the first method (ConfigureAuth), it appears in the class file "Startup.Auth.cs". The second file appears in the class file "Startup.cs". How can I organize the classes like that?

Solution

  • You can use partial classes in C# to split a big class into several files. Refactoring a big class is often better but there are some legitimate reasons to have big classes.

    Another use of partial classes is to allow a code generated class to be manually modified. The code generated part of the class goes into one file while the manual changes are kept in a separate file. In your case there is a single Startup class that are built from seperate source files handling seperate parts of the startup. Some of these files can be added by NuGet packages and using a partial class greatly simplifices how different features are included in your application.

    It is quite simple to split a class into several source files using partial:

    Assume you have a class implemented in the source file MyClass.cs:

    class MyClass {

  public void MethodA() { ... }

  public void MethodB() { ... }

}

    You can then split it into two source files. MyClass.A.cs:

    partial class MyClass {

  public void MethodA() { ... }

}

    And MyClass.B.cs:

    partial class MyClass {

  public void MethodB() { ... }

}

    So by marking the class as partial you are allowed to spread the contents of the class across several instances of class constructs. The compiler will merge them all into a single class definition during compilation.

    You can study the details about partial classes on MSDN.