Under what conditions it is good to have a "partial class?"

Question

When does it become a good idea to have your class separate into two .cs and have it as a partial class?

Are there some signs showing that it is time to go with partial class?

Thanks!

Answer 1

When you have to autogenerate a portion of those classes and manually write the rest of the content of the classes.

This is so that you can put the machine-generated content in one file and hand-coded code in another file. The advantage of doing so is that when you have to regenerate the source code, your hand-coded portion won't get wiped out.

This is how MS generates class content for its GUI designers ( think of those *.designer.cs file), and allows you to put the meat of your logic in other related file ( *.cs)

Answer 2

Like the others said, auto-generated code is a good reason. I also use partial class sometimes when I want to put a nested class in its own file.

public partial class MyClass
{
    private class NestedClass
    {
        ...
    }
}

Plus there is this little trick to nest a file in the solution explorer (to do like winform and nest the Form1.designer.cs file).

<Compile Include="Foo.1.cs">
  <DependentUpon>Foo.cs</DependentUpon>
</Compile>

Nesting file in Visual Studio

Answer 3

If you have auto-generated code you want to extend, a partial class is a great way to do that.

For example, extending LINQ to SQL classes that get generated.