code 39 vb.net Reflecting Over an AppDomain s Assemblies in Visual Studio .NET

Painting Code 39 in Visual Studio .NET Reflecting Over an AppDomain s Assemblies

The Reflector sample is a good introduction to reflection because it shows how to reflect over an assembly s metadata. At times, however, you might want to reflect over all the assemblies contained within an AppDomain. To demonstrate how to reflect over all the assemblies in an AppDomain, I took the Reflector sample application and made a small change to the Main method. Here s the new Main method (nothing else has changed):

static void Main() { foreach (Assembly assem in AppDomain.CurrentDomain.GetAssemblies()) { Reflector.ReflectOnAssembly(assem); } }

In this version of Main, System.AppDomain s static CurrentDomain property is called. This property returns a reference to an AppDomain object that identifies the AppDomain containing the calling code. Then the AppDomain object s GetAssemblies method is called, which returns an array of System.Reflection.Assembly elements one element for each assembly loaded into the AppDomain at the time GetAssemblies is called. At this point, a loop iterates over the array of assemblies, calling Reflector s static ReflectOnAssembly method for each one. This version of the Reflector application shows all the assemblies in the AppDomain, all the modules that make up each assembly, all the types defined by each module, and all the members defined by each type. If you build and run this version of the Reflector sample application, you ll see that two assemblies are shown in the output: MSCorLib.dll and Reflector.exe. Because MSCorLib.dll defines over 1400 types, the output produced by this application is much too long to reprint in this book.

In the second version of the Reflector application, a type s members are obtained by calling the Type object s GetMembers method. Type actually offers two versions of the GetMembers method. The first overload takes no parameters. This version returns the type s publicly defined static and instance members only. The second overload of GetMembers takes a single parameter: an instance of a System.Reflection.BindingFlags enumerated type. Table 20 2 shows the relevant symbols defined by the BindingFlags enumerated type. Table 20 2: Search Symbols Defined by the BindingFlags Enumerated Type Symbol Default Value 0x00 Description A placeholder for no flags specified. Use this flag when you don t want to specify any of the flags in the remainder of this table. Search using case insensitivity. Only search members on the declared type. (Ignore inherited members.) Search instance members. Search static members. Search public members. Search nonpublic members. Search static members defined by base types.

Earlier, I pointed out that Reflector s output doesn t include a type s private members. You can specify exactly which members the GetMembers method should return by passing the desired BindingFlags when calling this method. To reflect over the nonpublic members of a type, I ve modified the original Reflector sample application again. In this version, I ve now told GetMembers to return all public and nonpublic, and static and instance members that are declared by the type itself. Any members inherited from a base type are not displayed. Here s what the new code to call GetMembers looks like (nothing else in the source code has changed):

BindingFlags bf = BindingFlags.DeclaredOnly | BindingFlags.NonPublic | BindingFlags.Public | BindingFlags.Instance | BindingFlags.Static; foreach (MemberInfo mi in t.GetMembers(bf)) WriteLine(3, "{0}: {1}", mi.MemberType, mi);

Here, bf is initialized to a set of flags, indicating that I want to iterate over the type s public and nonpublic, and static and instance members. Furthermore, the DeclaredOnly flag indicates that I only want to iterate over the members that the type defines not any of the members that the type inherits. Once bf is initialized, it is passed to the GetMembers method, which now knows exactly what members I m interested in processing. After making the above change to the Reflector source code, building and running the new version of this application yields the following output: