Recipe 13.15. Accessing Local Variable Information

Problem

You are building a tool that examines code and you need to get access to the local variables within a method.

Solution

Use the LocalVariables property on the MethodBody class to return an IList of LocalVariableInfo objects, each of which describes a local variable within the method:

	public static IList<LocalVariableInfo> GetLocalVars(string asmPath,
	                                    string typeName, string methodName)
	{
	    Assembly asm = Assembly.LoadFrom(asmPath);
	    Type asmType = asm.GetType(typeName);
	    MethodInfo mi = asmType.GetMethod(methodName);
	    MethodBody mb = mi.GetMethodBody();

	    IList<LocalVariableInfo> vars = mb.LocalVariables;

	    // Display information about each local variable.
	    foreach (LocalVariableInfo lvi in vars)
	    {
	        Console.WriteLine("IsPinned: " + lvi.IsPinned);
	        Console.WriteLine("LocalIndex: " + lvi.LocalIndex);
	        Console.WriteLine("LocalType.Module: " + lvi.LocalType.Module);
	        Console.WriteLine("LocalType.FullName: " + lvi.LocalType.FullName);
	        Console.WriteLine("ToString(): " + lvi.ToString());
	    }

	    return (vars);
	}

The GetLocalVars method can be called using the following code:

	public static void TestGetLocalVars()
	{
	    Process current = Process.GetCurrentProcess();

	    // Get the path of the current module.
	    string path = current.MainModule.FileName;

	    // Get all local var info for the CSharpRecipes.Reflection.GetLocalVars method.
	    System.Collections.ObjectModel.ReadOnlyCollection<LocalVariableInfo> vars =
	        (System.Collections.ObjectModel.ReadOnlyCollection<LocalVariableInfo>)
	        GetLocalVars(path, "CSharpRecipes.Reflection", "GetLocalVars");
	}

The output of this method is shown here:

	IsPinned: False
	LocalIndex: 0
	LocalType.Module: CommonLanguageRuntimeLibrary
	LocalType.FullName: System.Reflection.Assembly
	ToString( ): System.Reflection.Assembly (0)
	IsPinned: False
	LocalIndex: 1
	LocalType.Module: CommonLanguageRuntimeLibrary
	LocalType.FullName: System.Type
	ToString( ): System.Type (1)
	IsPinned: False
	LocalIndex: 2
	LocalType.Module: CommonLanguageRuntimeLibrary
	LocalType.FullName: System.Reflection.MethodInfo
	ToString( ): System.Reflection.MethodInfo (2)
	IsPinned: False
	LocalIndex: 3
	LocalType.Module: CommonLanguageRuntimeLibrary
	LocalType.FullName: System.Reflection.MethodBody
	ToString( ): System.Reflection.MethodBody (3)
	IsPinned: False
	LocalIndex: 4
	LocalType.Module: CommonLanguageRuntimeLibrary
	LocalType.FullName: System.Collections.ObjectModel.ReadOnlyCollection`1[[System.
	Reflection.LocalVariableInfo, mscorlib, Version=2.0.0.0, Culture=neutral, Public
	KeyToken=b77a5c561934e089]]
	ToString( ): System.Collections.ObjectModel.ReadOnlyCollection`1[System.Reflectio
	n.LocalVariableInfo] (4)

The LocalVariableInfo objects for each local variable found in the CSharpRecipes. Reflection.GetLocalVars method will be returned in the vars IList collection.

Discussion

The LocalVariables property can give you a good amount of information about variables within a method. The LocalVariables property returns an IList<LocalVariableInfo> collection. Each LocalVariableInfo object contains the information described in Table 13-5.

Table 13-5. LocalVariableInfo information

Member	Definition
IsPinned	Returns a bool indicating if the object that this variable refers to is pinned in memory (TRue) or not (false)
LocalIndex	Returns the index of this variable within this method's body
LocalType	Returns a Type object that describes the type of this variable
ToString	Returns the LocalType.FullName, a space, and then the LocalIndex value surrounded by parentheses

See Also

See the "MethodInfo Class," "MethodBody Class," "ReadOnlyCollection<T> Class," and "LocalVariableInfo Class" topics in the MSDN documentation.