3.10 Retrieve Type Information

Problem

You need to obtain a System.Type object that represents a specific type.

Solution

Use one of the following:

• The typeof operator

• The static GetType method of the System.Type class

• The GetType method of an existing instance of the type

• The GetNestedType or GetNestedTypes methods of the Type class

• The GetType or GetTypes methods of the Assembly class

• The GetType , GetTypes , or FindTypes methods of the System.Reflection.Module class

Discussion

The Type object provides a starting point for working with types using reflection. A Type object allows you to inspect the metadata of the type, obtain details of the type's members , and create instances of the type. Because of its importance, the .NET Framework provides a variety of mechanisms for obtaining reference to Type objects.

The most efficient method of obtaining a Type object for a specific type is to use the typeof operator shown here.

 System.Type t1 = typeof(System.Text.StringBuilder); 

The type name isn't enclosed in quotes and must be resolvable by the compiler. Because the reference is resolved at compile time, the assembly containing the type becomes a static dependency of your assembly and will be listed as such in your assembly's manifest.

An alternative to the typeof operator is the static method Type.GetType , which takes a string containing the type name. Because you use a string to specify the type, you can vary it at run time, which opens the door to a world of dynamic programming opportunities using reflection (see recipe 3.12). If you specify just the type name, the runtime must be able to locate the type in an already loaded assembly. Alternatively, you can specify an assembly-qualified type name. Refer to the .NET Framework SDK documentation for the Type.GetType method for a complete description of how to structure assembly-qualified type names . The following statements demonstrate the use of the GetType method:

 // Case sensitive, return null if not found Type t2 = Type.GetType("System.String"); // Case sensitive, throw TypeLoadException if not found Type t3 = Type.GetType("System.String", true); // Case insensitive, throw TypeLoadException if not found Type t4 = Type.GetType("system.string", true, true); // Assembly qualifed type name Type t5 = Type.GetType("System.Data.DataSet,System.Data," +     "Version=1.0.5000.0,Culture=neutral,PublicKeyToken=b77a5c561934e089"); 

To obtain a Type object representing the type of an existing object, use the GetType method, implemented by Object and inherited by all types. Here's an example:

 System.Text.StringBuilder sb = new System.Text.StringBuilder(); Type t6 = sb.GetType(); 

Table 3.2 summarizes other methods that provide access to Type objects.

Table 3.2: Methods That Return Type Objects

Method	Description
Type.GetNestedType	Gets a specified type declared as a nested type within the existing Type object
Type.GetNestedTypes	Gets an array of Type objects representing the nested types declared within the existing Type object
Assembly.GetType	Gets a Type object for the specified type declared within the assembly
Assembly.GetTypes	Gets an array of Type objects representing the types declared within the assembly
Module.GetType	Gets a Type object for the specified type declared within the module
Module.GetTypes	Gets an array of Type objects representing the types declared within the module
Module.FindTypes	Gets a filtered array of Type objects representing the types declared within the module ”the types are filtered using a delegate that determines if each Type should appear in the final array