Vanara/Core/Extensions/ReflectionExtensions.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Reflection;
using System.Reflection.Emit;

namespace Vanara.Extensions
{
	/// <summary>Extensions related to <c>System.Reflection</c></summary>
	public static class ReflectionExtensions
	{
		/// <summary>Gets all loaded types in the <see cref="AppDomain"/>.</summary>
		/// <param name="appDomain">The application domain.</param>
		/// <returns>All loaded types.</returns>
		public static IEnumerable<Type> GetAllTypes(this AppDomain appDomain) => appDomain.GetAssemblies().SelectMany(a => a.GetTypes());

		/// <summary>Returns an array of custom attributes applied to this member and identified by <typeparamref name="TAttr"/>.</summary>
		/// <typeparam name="TAttr">The type of attribute to search for. Only attributes that are assignable to this type are returned.</typeparam>
		/// <param name="element">An object derived from the MemberInfo class that describes a constructor, event, field, method, or property member of a class.</param>
		/// <param name="inherit"><c>true</c> to search this member's inheritance chain to find the attributes; otherwise, <c>false</c>. This parameter is ignored for properties and events.</param>
		/// <param name="predicate">An optional predicate to refine the results.</param>
		/// <returns></returns>
		public static IEnumerable<TAttr> GetCustomAttributes<TAttr>(this MemberInfo element, bool inherit = false, Func<TAttr, bool> predicate = null) where TAttr : Attribute =>
			element.GetCustomAttributes(typeof(TAttr), inherit).Cast<TAttr>().Where(predicate ?? (a => true));

		/// <summary>Returns an array of custom attributes applied to this member and identified by <typeparamref name="TAttr"/>.</summary>
		/// <typeparam name="TAttr">The type of attribute to search for. Only attributes that are assignable to this type are returned.</typeparam>
		/// <param name="type">The type of the <see cref="Type"/> to examine.</param>
		/// <param name="inherit"><c>true</c> to search this member's inheritance chain to find the attributes; otherwise, <c>false</c>. This parameter is ignored for properties and events.</param>
		/// <param name="predicate">An optional predicate to refine the results.</param>
		/// <returns></returns>
		public static IEnumerable<TAttr> GetCustomAttributes<TAttr>(this Type type, bool inherit = false, Func<TAttr, bool> predicate = null) where TAttr : Attribute =>
			type.GetCustomAttributes(typeof(TAttr), inherit).Cast<TAttr>().Where(predicate ?? (a => true));

		/// <summary>Gets a named property value from an object.</summary>
		/// <typeparam name="T">The expected type of the property to be returned.</typeparam>
		/// <param name="obj">The object from which to retrieve the property.</param>
		/// <param name="propertyName">Name of the property.</param>
		/// <param name="defaultValue">The default value to return in the instance that the property is not found.</param>
		/// <returns>The property value, if found, or the <paramref name="defaultValue"/> if not.</returns>
		public static T GetPropertyValue<T>(this object obj, string propertyName, T defaultValue = default(T))
		{
			var prop = obj.GetType().GetProperty(propertyName, BindingFlags.Public | BindingFlags.NonPublic | BindingFlags.Instance, null, typeof(T), Type.EmptyTypes, null);
			if (prop == null) return defaultValue;
			var val = prop.GetValue(obj, null);
			if (val == null) return defaultValue;
			return (T)val;
		}

		/// <summary>Invokes a named method on a created instance of a type with parameters.</summary>
		/// <typeparam name="T">The expected type of the method's return value.</typeparam>
		/// <param name="type">The type to be instantiated and then used to invoke the method. This method assumes the type has a default public constructor.</param>
		/// <param name="methodName">Name of the method.</param>
		/// <param name="args">The arguments to provide to the method invocation.</param>
		/// <returns>The value returned from the method.</returns>
		public static T InvokeMethod<T>(this Type type, string methodName, params object[] args)
		{
			var o = Activator.CreateInstance(type);
			return InvokeMethod<T>(o, methodName, args);
		}

		/// <summary>Invokes a named method on a created instance of a type with parameters.</summary>
		/// <typeparam name="T">The expected type of the method's return value.</typeparam>
		/// <param name="type">The type to be instantiated and then used to invoke the method.</param>
		/// <param name="instArgs">The arguments to supply to the constructor.</param>
		/// <param name="methodName">Name of the method.</param>
		/// <param name="args">The arguments to provide to the method invocation.</param>
		/// <returns>The value returned from the method.</returns>
		public static T InvokeMethod<T>(this Type type, object[] instArgs, string methodName, params object[] args)
		{
			var o = Activator.CreateInstance(type, instArgs);
			return InvokeMethod<T>(o, methodName, args);
		}

		/// <summary>Invokes a named method on an object with parameters and no return value.</summary>
		/// <param name="obj">The object on which to invoke the method.</param>
		/// <param name="methodName">Name of the method.</param>
		/// <param name="args">The arguments to provide to the method invocation.</param>
		public static void InvokeMethod(this object obj, string methodName, params object[] args)
		{
			var argTypes = args == null || args.Length == 0 ? Type.EmptyTypes : Array.ConvertAll(args,
				o => o?.GetType() ?? typeof(object));
			InvokeMethod(obj, methodName, argTypes, args);
		}

		/// <summary>Invokes a named method on an object with parameters and no return value.</summary>
		/// <typeparam name="T">The expected type of the method's return value.</typeparam>
		/// <param name="obj">The object on which to invoke the method.</param>
		/// <param name="methodName">Name of the method.</param>
		/// <param name="args">The arguments to provide to the method invocation.</param>
		/// <returns>The value returned from the method.</returns>
		public static T InvokeMethod<T>(this object obj, string methodName, params object[] args)
		{
			var argTypes = args == null || args.Length == 0 ? Type.EmptyTypes : Array.ConvertAll(args,
				o => o?.GetType() ?? typeof(object));
			return InvokeMethod<T>(obj, methodName, argTypes, args);
		}

		/// <summary>Invokes a named method on an object with parameters and no return value.</summary>
		/// <param name="obj">The object on which to invoke the method.</param>
		/// <param name="methodName">Name of the method.</param>
		/// <param name="argTypes">The argument types.</param>
		/// <param name="args">The arguments to provide to the method invocation.</param>
		public static void InvokeMethod(this object obj, string methodName, Type[] argTypes, object[] args)
		{
			var mi = obj?.GetType().GetMethod(methodName, argTypes);
			if (mi == null) throw new ArgumentException(@"Method not found", nameof(methodName));
			mi.Invoke(obj, args);
		}

		/// <summary>Invokes a named method on an object with parameters and no return value.</summary>
		/// <typeparam name="T">The expected type of the method's return value.</typeparam>
		/// <param name="obj">The object on which to invoke the method.</param>
		/// <param name="methodName">Name of the method.</param>
		/// <param name="argTypes">The argument types.</param>
		/// <param name="args">The arguments to provide to the method invocation.</param>
		/// <returns>The value returned from the method.</returns>
		public static T InvokeMethod<T>(this object obj, string methodName, Type[] argTypes, object[] args)
		{
			var mi = obj?.GetType().GetMethod(methodName, argTypes);
			if (mi == null) throw new ArgumentException(@"Method not found", nameof(methodName));
			var tt = typeof(T);
			if (tt != typeof(object) && mi.ReturnType != tt && !mi.ReturnType.IsSubclassOf(tt))
				throw new ArgumentException(@"Return type mismatch", nameof(T));
			return (T)mi.Invoke(obj, args);
		}

#if !(NETSTANDARD2_0)
		/// <summary>Invokes a method from a derived base class.</summary>
		/// <param name="methodInfo">The <see cref="MethodInfo"/> instance from the derived class for the method to invoke.</param>
		/// <param name="targetObject">The target object.</param>
		/// <param name="arguments">The arguments.</param>
		/// <returns>The value returned from the method.</returns>
		public static object InvokeNotOverride(this MethodInfo methodInfo, object targetObject, params object[] arguments)
		{
			var parameters = methodInfo.GetParameters();
			if (parameters.Length != arguments.Length)
				throw new Exception("Arguments count doesn't match");

			Type returnType = null;
			if (methodInfo.ReturnType != typeof(void))
				returnType = methodInfo.ReturnType;

			var type = targetObject.GetType();
			var dynamicMethod = new DynamicMethod("", returnType, new [] { type, typeof(object) }, type);
			var iLGenerator = dynamicMethod.GetILGenerator();
			iLGenerator.Emit(OpCodes.Ldarg_0); // this

			for (var i = 0; i < parameters.Length; i++)
			{
				var parameter = parameters[i];

				iLGenerator.Emit(OpCodes.Ldarg_1); // load array argument

				// get element at index
				iLGenerator.Emit(OpCodes.Ldc_I4_S, i); // specify index
				iLGenerator.Emit(OpCodes.Ldelem_Ref); // get element

				var parameterType = parameter.ParameterType;
				iLGenerator.Emit(OpCodes.Unbox_Any, parameterType);
			}

			iLGenerator.Emit(OpCodes.Call, methodInfo);
			iLGenerator.Emit(OpCodes.Ret);

			return dynamicMethod.Invoke(null, new [] { targetObject, arguments });
		}
#endif

		/// <summary>Loads a type from a named assembly.</summary>
		/// <param name="typeName">Name of the type.</param>
		/// <param name="asmRef">The name or path of the file that contains the manifest of the assembly.</param>
		/// <returns>The <see cref="Type"/> reference, or <c>null</c> if type or assembly not found.</returns>
		public static Type LoadType(string typeName, string asmRef = null)
		{
			Type ret = null;
			Assembly asm = null;
			try { asm = Assembly.LoadFrom(asmRef); } catch { }
			if (!TryGetType(asm, typeName, ref ret))
			{
				foreach (var asm2 in AppDomain.CurrentDomain.GetAssemblies())
					if (TryGetType(asm2, typeName, ref ret)) break;
			}
			return ret;
		}

		/// <summary>Tries the retrieve a <see cref="Type"/> reference from an assembly.</summary>
		/// <param name="typeName">Name of the type.</param>
		/// <param name="asm">The assembly from which to load the type.</param>
		/// <param name="type">The <see cref="Type"/> reference, if found.</param>
		/// <returns><c>true</c> if the type was found in the assembly; otherwise, <c>false</c>.</returns>
		private static bool TryGetType(Assembly asm, string typeName, ref Type type)
		{
			if (asm == null) return false;
			return (type = asm.GetType(typeName, false, false)) != null;
		}
	}
}