Web Page Extensions to Associate Domain Models With Web Forms

namespace System.Web.UI
{
    using System;
    using System.Reflection;
    using System.Collections.Generic;
    using System.ComponentModel.DataAnnotations;

    /// <summary>
    /// Provides validation information of the model instance.
    /// </summary>
    /// <typeparam name="T">Type of model object.</typeparam>
    public class ModelStateValidator<T> : Dictionary<String, String>
    {
        T model;
        RequiredAttribute required;
        RangeAttribute range;
        RegularExpressionAttribute regex;
        StringLengthAttribute stringlngt;

        /// <summary>
        /// Creates a new instance of the current System.Object
        /// </summary>
        /// <param name="model">Model instace to validate.</param>
        public ModelStateValidator(T model)
        {
            this.model = model;
        }

        /// <summary>
        /// Indicating whether this instance of the model is valid asper validation rules applied.
        /// </summary>
        public virtual bool IsValid
        {
            get
            {
                bool isValid = true;
                foreach (PropertyInfo property in typeof(T).GetProperties())
                {
                    //// If RequiredAttribute is defined, checks whether the property is valid of not.
                    if (property.GetCustomAttributes(typeof(RequiredAttribute), false).Length > 0)
                    {
                        required = (RequiredAttribute)property.GetCustomAttributes(typeof(RequiredAttribute), false)[0];
                        if (!required.IsValid(property.GetValue(model, null)))
                        {
                            isValid = false;
                            this.Add(property.Name, String.IsNullOrEmpty(required.ErrorMessage) ? property.Name + " is required." : required.ErrorMessage);
                        }
                    }
                    //// If RangeAttribute is defined, checks whether the property is valid of not.
                    else if (property.GetCustomAttributes(typeof(RangeAttribute), false).Length > 0)
                    {
                        range = (RangeAttribute)property.GetCustomAttributes(typeof(RangeAttribute), false)[0];
                        if (!range.IsValid(property.GetValue(model, null)))
                        {
                            isValid = false;
                            this.Add(property.Name, String.IsNullOrEmpty(range.ErrorMessage) ? property.Name + " is invalid." : range.ErrorMessage);
                        }
                    }
                    //// If RegularExpressionAttribute is defined, checks whether the property is valid of not.
                    else if (property.GetCustomAttributes(typeof(RegularExpressionAttribute), false).Length > 0)
                    {
                        regex = (RegularExpressionAttribute)property.GetCustomAttributes(typeof(RegularExpressionAttribute), false)[0];
                        if (!regex.IsValid(property.GetValue(model, null)))
                        {
                            isValid = false;
                            this.Add(property.Name, String.IsNullOrEmpty(regex.ErrorMessage) ? property.Name + " is invalid." : regex.ErrorMessage);
                        }
                    }
                    //// If StringLengthAttribute is defined, checks whether the property is valid of not.
                    else if (property.GetCustomAttributes(typeof(StringLengthAttribute), false).Length > 0)
                    {
                        stringlngt = (StringLengthAttribute)property.GetCustomAttributes(typeof(StringLengthAttribute), false)[0];
                        if (!stringlngt.IsValid(property.GetValue(model, null)))
                        {
                            isValid = false;
                            this.Add(property.Name, String.IsNullOrEmpty(stringlngt.ErrorMessage) ? property.Name + " exceeds maximum length." : stringlngt.ErrorMessage);
                        }
                    }
                }
                return isValid;
            }
        }
    }
}