的确，Partial Class用于自动代码生成，其中一个用途是维护一个可能有上千行代码的大型类文件。你永远不知道你的类最终会有1万行，你不想用不同的名字创建一个新类。

public partial class Product
{
    // 50 business logic embedded in methods and properties..
}

public partial class Product
{
    // another 50 business logic embedded in methods and properties..
}
//finally compile with product.class file.

另一个可能的用途是多个开发人员可以使用同一个类，因为它们存储在不同的地方。人们可能会笑，但你永远不知道有时候情况会很棘手。

Product1.cs

public partial class Product
{
    //you are writing the business logic for fast moving product
}

Product2.cs

public partial class Product
{
    // Another developer writing some business logic...
}

希望这是有意义的!

服务引用是另一个例子，其中部分类用于将生成的代码与用户创建的代码分开。

您可以在更新服务引用时“扩展”服务类，而不必覆盖它们。

从MSDN:

1.在编译时，合并部分类型定义的属性。例如，考虑以下声明:

[SerializableAttribute]
partial class Moon { }

[ObsoleteAttribute]
partial class Moon { }

它们等价于以下声明:

[SerializableAttribute]
[ObsoleteAttribute]
class Moon { }

以下是所有部分类型定义的合并:

XML注释 接口 泛型类型参数属性 类属性 成员

2.另外，嵌套的分部类也可以是分部类:

partial class ClassWithNestedClass
{
    partial class NestedClass { }
}

partial class ClassWithNestedClass
{
    partial class NestedClass { }
}

在处理大型类时，或在团队中工作时，尽可能保持所有内容的干净，您可以在不重写的情况下编辑(或始终提交更改)

每当我有一个类，其中包含一个具有重要大小/复杂性的嵌套类时，我将该类标记为partial，并将嵌套类放在一个单独的文件中。我使用规则命名包含嵌套类的文件:[class name]。[嵌套类名].cs。

下面的MSDN博客解释了如何使用带有嵌套类的部分类来实现可维护性:http://blogs.msdn.com/b/marcelolr/archive/2009/04/13/using-partial-classes-with-nested-classes-for-maintainability.aspx

Multiple Developer Using Partial Classes multiple developer can work on the same class easily. Code Generator Partial classes are mainly used by code generator to keep different concerns separate Partial Methods Using Partial Classes you can also define Partial methods as well where a developer can simply define the method and the other developer can implement that. Partial Method Declaration only Even the code get compiled with method declaration only and if the implementation of the method isn't present compiler can safely remove that piece of code and no compile time error will occur. To verify point 4. Just create a winform project and include this line after the Form1 Constructor and try to compile the code partial void Ontest(string s);

以下是在实现分部类时需要考虑的几点

Use partial keyword in each part of partial class. The name of each part of partial class should be the same but the source file name for each part of partial class can be different. All parts of a partial class should be in the same namespace. Each part of a partial class should be in the same assembly or DLL, in other words you can't create a partial class in source files from a different class library project. Each part of a partial class must have the same accessibility. (i.e: private, public or protected) If you inherit a class or interface on a partial class then it is inherited by all parts of that partial class. If a part of a partial class is sealed then the entire class will be sealed. If a part of partial class is abstract then the entire class will be considered an abstract class.