The partial keyword allows the class, struct, or interface to span across multiple files. Typically, a class will reside entirely in a single file. However, in situations where multiple developers need access to the same class, or more likely in the situation where a code generator of some type is generating part of a class, then having the class in multiple files can be beneficial.
The way that the partial keyword is used is to simply place partial before class, struct , or interface . In the following example the class TheBigClass resides in two separate source files, BigClassPart1.cs and BigClassPart2.cs :
//BigClassPart1.cs
partial class TheBigClass
{
public void MethodOne()
{
}
}
//BigClassPart2.cs
partial class TheBigClass
{
public void MethodTwo()
{
}
}
When the project that these two source files are part of is compiled, a single type called TheBigClass will be created with two methods, MethodOne() and MethodTwo().