/Sample/Sample.ViewModels.WPF+WinRT/ValidationViewModel.cs

using System;

using System.ComponentModel.DataAnnotations;

using System.Linq;

using System.Reactive;

using System.Reactive.Linq;

using System.Windows;

using Codeplex.Reactive;

using Codeplex.Reactive.Extensions;



namespace Sample.ViewModels

{

    public class ValidationViewModel

    {

        [Required]

        [Range(0, 100)]

        public ReactiveProperty<string> ValidationAttr { get; private set; }

        public ReactiveProperty<string> ValidationData { get; private set; }

        [StringLength(5)]

        public ReactiveProperty<string> ValidationBoth { get; private set; }

        public ReactiveProperty<string> ErrorInfo { get; private set; }

        public ReactiveCommand NextCommand { get; private set; }

        public ReactiveProperty<string> AlertMessage { get; private set; }



        public ValidationViewModel()

        {

            // DataAnnotation Attribute, call SetValidateAttribute and select self property

            // Note:error result dispatch to IDataErrorInfo, not exception.

            //      therefore, XAML is ValidatesOnDataErrors=True

            ValidationAttr = new ReactiveProperty<string>()

                .SetValidateAttribute(() => ValidationAttr);



            // IDataErrorInfo, call SetValidateError and set validate condition

            // null is success(have no error), string is error message

            ValidationData = new ReactiveProperty<string>()

                .SetValidateNotifyError((string s) => 

                    string.IsNullOrEmpty(s) ? 

                        "required" :

                        s.Cast<char>().All(Char.IsUpper) ? 

                            null : 

                            "not all uppercase");



            // Can set both validation

            ValidationBoth = new ReactiveProperty<string>()

                .SetValidateAttribute(() => ValidationBoth)

                .SetValidateNotifyError((string s) => string.IsNullOrEmpty(s) ? 

                    "required" : 

                    s.Cast<char>().All(Char.IsLower) ? 

                        null : 

                        "not all lowercase");



            // Validation result is pushed to ObserveErrorChanged

            var errors = Observable.Merge(

                ValidationAttr.ObserveErrorChanged,

                ValidationData.ObserveErrorChanged,

                ValidationBoth.ObserveErrorChanged);



            // Use OfType, choose error source

            ErrorInfo = Observable.Merge(

                    errors.Where(o => o == null).Select(_ => ""), // success

                    errors.OfType<Exception>().Select(e => e.Message), // from attribute

                    errors.OfType<string>()) // from IDataErrorInfo

                .ToReactiveProperty();



            // Validation is view initialized not run in default.

            // If want to validate on view initialize,

            // use ReactivePropertyMode.RaiseLatestValueOnSubscribe to ReactiveProperty

            // that mode is validate values on initialize.

            NextCommand = ValidationAttr.ObserveErrorChanged

                .CombineLatest(

                    ValidationData.ObserveErrorChanged,

                    ValidationBoth.ObserveErrorChanged, 

                    (a, b, c) => new[] { a, b, c }.All(x => x == null))

                .ToReactiveCommand(initialValue: false);

            this.AlertMessage = this.NextCommand.Select(_ => "Can go to next!")

                .ToReactiveProperty(mode: ReactivePropertyMode.None);

        }

    }

}