Can I split my C# class across multiple files?

Question

I have a class that looks like this:

public static class ReferenceData
{

    public static IEnumerable<SelectListItem> GetAnswerType()
    {
        return new[]
            {
                new SelectListItem { Value = "1", Text = "1 answer"  },
                new SelectListItem { Value = "2", Text = "2 answers" },
                new SelectListItem { Value = "3", Text = "3 answers" }
            };
    }

    public static IEnumerable<SelectListItem> GetDatastore()
    {
        return new[]
            {
                new SelectListItem { Value = "DEV", Text = "Development"  },
                new SelectListItem { Value = "DC1", Text = "Production" }
            };
    }
    public static string GetDatastoreText(string datastoreValue)
    {
        return GetDatastore().Single(s => s.Value == datastoreValue).Text;
    }
    public static string GetDatastoreValue(string datastoreText)
    {
        return GetDatastore().Single(s => s.Text == datastoreText).Value;
    }

    // Lots more here
    // Lots more here

}

There's a lot more that I didn't show above.

Currently all of the class information is in one file. However I would like to split this into multiple files. Is there some way that I can spread the contents of the ReferenceData class across more than one file?

Mark Byers · Accepted Answer · 2011-10-29 13:05:39Z

58

Yes, you can use partial classes. This allows you to split your class over multiple files.

File 1:

public static partial class ReferenceData
{
    /* some methods */
}

File 2:

public static partial class ReferenceData
{
    /* some more methods */
}

Use this feature carefully. Overuse can make it hard to read the code.

edited Oct 29, 2011 at 13:05

answered Oct 29, 2011 at 12:58

Mark Byers

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2 Comments

Jason Williams Over a year ago

+1. However, consider using regions to organise the code better within a single file. If you still 'need' several files it is usually a sign that your class is not well designed. Consider breaking it into several classes with clearly defined jobs/behaviours.

Tesserex Over a year ago

@JasonWilliams Agreed but keep in mind that there are cases where partial classes are necessary, such as in asp mvc where half the class is auto-generated, and you may want to add to it.

Tesserex · Accepted Answer · 2011-10-29 12:57:45Z

45

Yes, include the keyword partial in the class declaration in every file where you do so.

http://msdn.microsoft.com/en-us/library/wa80x488.aspx

answered Oct 29, 2011 at 12:57

Tesserex

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1 Comment

Jehonathan Thomas Over a year ago

Partial classes must be having the same namespace, just an info.

FXQuantTrader · Accepted Answer · 2020-01-08 05:27:13Z

Yes you can of course, just use the partial keyword before the class keyword at all declarations. For example, make 4 different files (but in the same namespace) containing methods and members for the ReferenceData class like this:

File1.css

public static partial class ReferenceData
{

    public static IEnumerable<SelectListItem> GetAnswerType()
    {
        return new[]
            {
                new SelectListItem { Value = "1", Text = "1 answer"  },
                new SelectListItem { Value = "2", Text = "2 answers" },
                new SelectListItem { Value = "3", Text = "3 answers" }
            };
    }
}

File2.cs

public static partial class ReferenceData
{

    public static IEnumerable<SelectListItem> GetDatastore()
    {
        return new[]
            {
                new SelectListItem { Value = "DEV", Text = "Development"  },
                new SelectListItem { Value = "DC1", Text = "Production" }
            };
    }
}

File3.cs

public static partial class ReferenceData
{

    public static string GetDatastoreText(string datastoreValue)
    {
        return GetDatastore().Single(s => s.Value == datastoreValue).Text;
    }
    public static string GetDatastoreValue(string datastoreText)
    {
        return GetDatastore().Single(s => s.Text == datastoreText).Value;
    }
}

File4.cs

public static partial class ReferenceData
{

    // Lots more here
    // Lots more here
}

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