如何使用反射访问内部类

In general, you shouldn't do this - if a type has been marked internal, that means you're not meant to use it from outside the assembly. It could be removed, changed etc in a later version.

However, reflection does allow you to access types and members which aren't public - just look for overloads which take a BindingFlags argument, and include BindingFlags.NonPublic in the flags that you pass.

If you have the fully qualified name of the type (including the assembly information) then just calling Type.GetType(string) should work. If you know the assembly in advance, and know of a public type within that assembly, then using typeof(TheOtherType).Assembly to get the assembly reference is generally simpler, then you can call Assembly.GetType(string).

To load the assembly and type you quoted in your example:

Assembly design = Assembly.LoadFile(@"C:\WINDOWS\Microsoft.NET\Framework\v2.0.50727\System.Design.dll");
Type designHost = design.GetType("System.ComponentModel.Design.DesignerHost");