Reading assembly attributes at runtime using Reflection in .NET

A lot of metadata of an assembly is stored by way of attributes in the AssemblyInfo.cs file. E.g. if you create a simple Console application then this file will be readily available in the Properties folder. Assembly-related attributes are denoted by an “assembly:” prefix and can carry a lot of customisable information. Examples:

[assembly: AssemblyTitle("ReflectionCodeBits")]
[assembly: AssemblyDescription("This is a container for Reflection related code examples")]
[assembly: AssemblyConfiguration("")]
[assembly: AssemblyCompany("Great Company Ltd.")]
[assembly: AssemblyProduct("ReflectionCodeBits")]
[assembly: AssemblyCopyright("Copyright ©  2014")]
[assembly: AssemblyTrademark("GC")]
[assembly: AssemblyCulture("sv-SE")]
[assembly: ComVisible(false)]
[assembly: Guid("8376337d-c211-4507-bc0d-bcd39bc9fb4f")]
[assembly: AssemblyVersion("1.0.0.0")]
[assembly: AssemblyFileVersion("1.0.0.0")]

Most of these are self-explanatory but others deserve more attention:

• AssemblyConfiguration: to specify which configuration is used for the assembly. You can specify this value like “DEBUG”, “RELEASE” or some custom configuration name, like “ALPHA”
• AssemblyCulture: normally only used for satellite assemblies, otherwise an empty string denoting neutral culture – in fact you specify an assembly culture like I have done above you’ll get a compile error saying that executables cannot be satellite assemblies; culture should always be empty.

You can read the full documentation about assembly attributes here.

In order to extract the assembly attributes you’ll first need to get a reference to that assembly. You can then list all attributes of the assembly as follows:

Assembly executingAssembly = Assembly.GetExecutingAssembly();
IEnumerable<CustomAttributeData> assemblyAttributes = executingAssembly.CustomAttributes;
foreach (CustomAttributeData assemblyAttribute in assemblyAttributes)
{
	Type attributeType = assemblyAttribute.AttributeType;
	Console.WriteLine("Attribute type: {0}", attributeType);
	IList<CustomAttributeTypedArgument> arguments = assemblyAttribute.ConstructorArguments;
	Console.WriteLine("Attribute arguments: ");
	foreach (CustomAttributeTypedArgument arg in arguments)
	{
		Console.WriteLine(arg.Value);
	}
}

In my case I got the following output:

You can also extract a specific attribute type as follows:

AssemblyDescriptionAttribute assemblyDescriptionAttribute =     executingAssembly.GetCustomAttribute<AssemblyDescriptionAttribute>();
string assemblyDescription = assemblyDescriptionAttribute.Description;

…which returns “This is a container for Reflection related code examples” as expected.

View all posts on Reflection here.

Examining the Assembly using Reflection in .NET

The CLR code of a project is packaged into an assembly. We can inspect a range of metadata from an assembly that also the CLR uses to load and execute runnable code: classes, methods, interfaces, enumerations etc.

In order to inspect an Assembly in a .NET project we’ll first need to get a reference to the assembly in question. There are various ways to retrieve an assembly, including:

Assembly callingAssembly = Assembly.GetCallingAssembly();
Assembly entryAssembly = Assembly.GetEntryAssembly();
Assembly executingAssembly = Assembly.GetExecutingAssembly();

…where Assembly is located in the System.Reflection namespace.

The static methods above represent the following:

• GetCallingAssembly: to get the assembly one level up the call stack, i.e. which contains the method the current executing code
• GetEntryAssembly: to get the assembly which contains the entry point to the application, e.g. the Main method in a Console app
• GetExecutingAssembly: to get the assembly of the currently running code

There’s also a way to load a specific assembly using the GetAssembly(Type type) method. E.g. if you have a Customer class then you can load the assembly that contains the Customer class as follows:

Assembly specificAssembly = Assembly.GetAssembly(typeof(Customer));

Once you have the assembly you can read various metadata from it, examples:

Console.WriteLine("Full name: {0}", callingAssembly.FullName);
Console.WriteLine("Location: {0}", callingAssembly.Location);
Console.WriteLine("Loaded for reflection only? {0}", callingAssembly.ReflectionOnly);
Console.WriteLine("Loaded from GAC? {0}", callingAssembly.GlobalAssemblyCache);
Console.WriteLine(".NET Version: {0}", callingAssembly.ImageRuntimeVersion);

…which in my case outputs the following:

You may wonder what “loaded for reflection” means. You can get hold of an assembly in order to inspect its metadata without the possibility to execute any action on it. This is how we can load the assembly containing the “string” class in .NET:

Assembly reflectionOnlyAssembly = Assembly.ReflectionOnlyLoad("mscorlib, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089");

You can execute an assembly by creating an instance of it using the CreateInstance method. However, if the assembly was only loaded for reflection then CreateInstance will throw an exception. If you know that you only want to read some metadata from an assembly but not execute it then you can use the ReflectionOnlyLoad method to save time loading it fully into the AppDomain.

View all posts on Reflection here.