Validate with Custom Annotations in C#

Create Attributes

Create new folder named Attributes and create new attributes as below:

Email Attribute

Create new file named Email.cs as below:

using System;

namespace LearnAdvancedCSharpWithRealApps.Attributes
{
	[AttributeUsage(AttributeTargets.Field | AttributeTargets.Property)]
	public class Email : Attribute
	{
	}
}				

Max Annotation

Create new file named Max.cs as below:

using System;

namespace LearnAdvancedCSharpWithRealApps.Attributes
{
	[AttributeUsage(AttributeTargets.Field | AttributeTargets.Property)]
	public class Max : Attribute
	{
		public int Value { get; set; }
	}
}				

Min Annotation

Create new file named Min.cs as below:

using System;

namespace LearnAdvancedCSharpWithRealApps.Attributes
{
	[AttributeUsage(AttributeTargets.Field | AttributeTargets.Property)]
	public class Min : Attribute
	{
		public int Value { get; set; }
	}
}							

MinLength Annotation

Create new file named MinLength.cs as below:

using System;

namespace LearnAdvancedCSharpWithRealApps.Attributes
{
	[AttributeUsage(AttributeTargets.Field | AttributeTargets.Property)]
	public class MinLength : Attribute
	{
		public int Value { get; set; }
	}
}				

MaxLength Annotation

Create new file named MaxLength.cs as below:

using System;

namespace LearnAdvancedCSharpWithRealApps.Attributes
{
	[AttributeUsage(AttributeTargets.Field | AttributeTargets.Property)]
	public class MaxLength : Attribute
	{
		public int Value { get; set; }
	}
}						

NotEmpty Annotation

Create new file named NotEmpty.cs as below:

using System;

namespace LearnAdvancedCSharpWithRealApps.Attributes
{
	[AttributeUsage(AttributeTargets.Field | AttributeTargets.Property)]
	public class NotEmpty : Attribute
	{
	}
}			

URL Annotation

Create new file named URL.cs as below:

using System;

namespace LearnAdvancedCSharpWithRealApps.Attributes
{
	[AttributeUsage(AttributeTargets.Field | AttributeTargets.Property)]
	public class URL : Attribute
	{
	}
}		

Create Entity Class

Create Entities folder and create new class named Account.cs as below:

using LearnAdvancedCSharpWithRealApps.Attributes;

namespace LearnAdvancedCSharpWithRealApps.Entities
{
	public class Account
	{
		[NotEmpty]
		[MinLength(Value = 3)]
		[MaxLength(Value = 10)]
		public string Username { get; set; }

		[NotEmpty]
		[Email]
		public string Email { get; set; }

		[Min(Value = 18)]
		[Max(Value = 60)]
		public int Age { get; set; }

		[URL]
		public string Website { get; set; }
	}
}					

Run Application

using LearnAdvancedCSharpWithRealApps.Attributes;
using LearnAdvancedCSharpWithRealApps.Entities;
using System;
using System.Reflection;

namespace LearnAdvancedCSharpWithRealApps
{
	class Program
	{
		static void Main(string[] args)
		{
			var account = new Account
			{
				Username = "abca",
				Age = 22,
				Email = "aa@gmail.com",
				Website = "https://learningprogramming.net"
			};

			Console.WriteLine("Valid: " + isValid(account));

			Console.ReadLine();
		}

		private static bool isValid(object obj)
		{
			bool result = true;
			try
			{
				foreach (var propertyInfo in obj.GetType().GetProperties())
				{
					foreach (object ob in propertyInfo.GetCustomAttributes())
					{
						if (ob is NotEmpty)
						{
							var value = propertyInfo.GetValue(obj).ToString();
							if (string.IsNullOrEmpty(value))
							{
								result = false;
							}
						}
						if (ob is MinLength)
						{
							var minLength = ob as MinLength;
							var value = propertyInfo.GetValue(obj).ToString();
							if (value.Length < minLength.Value)
							{
								result = false;
							}
						}
						if (ob is MaxLength)
						{
							var maxLength = ob as MaxLength;
							var value = propertyInfo.GetValue(obj).ToString();
							if (value.Length > maxLength.Value)
							{
								result = false;
							}
						}
						if (ob is Min)
						{
							var min = ob as Min;
							var value = int.Parse(propertyInfo.GetValue(obj).ToString());
							if (value < min.Value)
							{
								result = false;
							}
						}
						if (ob is Max)
						{
							var max = ob as Max;
							var value = int.Parse(propertyInfo.GetValue(obj).ToString());
							if (value > max.Value)
							{
								result = false;
							}
						}
						if (ob is Email)
						{
							var value = propertyInfo.GetValue(obj).ToString();
							if (!IsValidEmail(value))
							{
								result = false;
							}
						}
						if (ob is URL)
						{
							var value = propertyInfo.GetValue(obj).ToString();
							if (!IsValidURL(value))
							{
								result = false;
							}
						}
					}
				}
			}
			catch
			{
				result = false;
			}
			return result;
		}

		private static bool IsValidURL(string url)
		{
			Uri uriResult;
			return Uri.TryCreate(url, UriKind.Absolute, out uriResult) && uriResult.Scheme == Uri.UriSchemeHttp;
		}

		private static bool IsValidEmail(string email)
		{
			try
			{
				var addr = new System.Net.Mail.MailAddress(email);
				return addr.Address == email;
			}
			catch
			{
				return false;
			}
		}

	}
}									

Structure of Project

Output

Valid: False