From 151e56ec2e3466389804b8874b4224bf6bd08097 Mon Sep 17 00:00:00 2001
From: Vitaly Takmazov
Date: Wed, 3 Apr 2013 05:03:20 +0400
Subject: New pages, LoginViewModel, Validation (in progress)

---
 Juick/App.xaml.cs                                | 25 +++++---
 Juick/Classes/AccountManager.cs                  | 62 +++++++++++---------
 Juick/Controls/MessageList.xaml                  |  2 +-
 Juick/Juick.csproj                               |  2 +
 Juick/LoginView.xaml                             | 36 +++++++-----
 Juick/LoginView.xaml.cs                          | 22 +++-----
 Juick/MainPage.xaml                              | 19 ++++---
 Juick/MainPage.xaml.cs                           | 55 ++++++++++--------
 Juick/NewPostView.xaml.cs                        |  2 +-
 Juick/ViewModels/LoginViewModel.cs               | 72 ++++++++++++++++++++++++
 Juick/ViewModels/PageViewModel.cs                |  4 +-
 Juick/ViewModels/Validation/DataViewModelBase.cs | 44 +++++++++++++++
 12 files changed, 245 insertions(+), 100 deletions(-)
 create mode 100644 Juick/ViewModels/LoginViewModel.cs
 create mode 100644 Juick/ViewModels/Validation/DataViewModelBase.cs

(limited to 'Juick')

diff --git a/Juick/App.xaml.cs b/Juick/App.xaml.cs
index 98dc31c..03e0d10 100644
--- a/Juick/App.xaml.cs
+++ b/Juick/App.xaml.cs
@@ -10,22 +10,31 @@ namespace Juick
 {
     public partial class App : Application
     {
-        public void NavigateTo(Uri param) {
-            RootFrame.Navigate(param);
+        public void NavigateTo(Uri param, bool removeFromStack = false)
+        {
+            var page = (PhoneApplicationPage) RootFrame.Content;
+            var service = page.NavigationService;
+            service.Navigate(param);
+            if (removeFromStack)
+            {
+                page.Dispatcher.BeginInvoke(() => service.RemoveBackEntry());
+            }
         }
-        private static AppViewModel context = null;
+        private static AppViewModel _context = null;
 
         public static AppViewModel AppContext
         {
             get
             {
                 // Delay creation of the view model until necessary
-                if (context == null) {
-                    context = new AppViewModel();
-                    context.Pages.Add(new PageViewModel(context) { RestUri = "/home?1=1" });
-                    context.Pages.Add(new PageViewModel(context) { RestUri = "/messages?1=1" });
+                if (_context == null) {
+                    _context = new AppViewModel();
+                    _context.Pages.Add(new PageViewModel(_context) { RestUri = "/home?1=1", Caption = "My feed"});
+                    _context.Pages.Add(new PageViewModel(_context) { RestUri = "/messages?1=1", Caption = "Last"});
+                    _context.Pages.Add(new PageViewModel(_context) { RestUri = "/messages?1=1&popular=1", Caption = "Top"});
+                    _context.Pages.Add(new PageViewModel(_context) { RestUri = "/messages?1=1&media=all", Caption = "Images" });
                 };
-                return context;
+                return _context;
             }
         }        
         /// <summary>
diff --git a/Juick/Classes/AccountManager.cs b/Juick/Classes/AccountManager.cs
index 8f8e366..4741992 100644
--- a/Juick/Classes/AccountManager.cs
+++ b/Juick/Classes/AccountManager.cs
@@ -1,53 +1,63 @@
 using System;
 using System.IO.IsolatedStorage;
 using System.Net;
+using System.Windows;
 using System.Windows.Controls;
 
 namespace Juick.Classes
 {
     public class AccountManager
     {
-        const string FileName = "account.xml";
-        public NetworkCredential Credentials
+        private string _userName;
+        private string _password;
+        
+        public string UserName
         {
             get
             {
-                string userName;
-                string password;
-                IsolatedStorageSettings.ApplicationSettings.TryGetValue<string>("user", out userName);
-                IsolatedStorageSettings.ApplicationSettings.TryGetValue<string>("password", out password);
-                return new NetworkCredential
-                           {
-                               UserName = userName,
-                               Password = password,
-                           };
+                if (_userName == null)
+                {
+                    IsolatedStorageSettings.ApplicationSettings.TryGetValue<string>("user", out _userName);    
+                }
+                return _userName;
             }
             set
             {
-                var creds = value;
-                if (creds != null)
-                {
-                    IsolatedStorageSettings.ApplicationSettings["user"] = value.UserName;
-                    IsolatedStorageSettings.ApplicationSettings["password"] = value.Password;
-                }
-                else
+                _userName = value;
+                IsolatedStorageSettings.ApplicationSettings["user"] = _userName;
+            }
+        }
+
+        public string Password
+        {
+            get
+            {
+                if (_password == null)
                 {
-                    IsolatedStorageSettings.ApplicationSettings["user"] = null;
-                    IsolatedStorageSettings.ApplicationSettings["password"] = null;
+                    IsolatedStorageSettings.ApplicationSettings.TryGetValue<string>("password", out _password);    
                 }
+                return _password;
+            }
+            set
+            {
+                _password = value;
+                IsolatedStorageSettings.ApplicationSettings["password"] = value;
             }
         }
 
-        public void SignIn(Page page, string login, string pass, Uri nextUri)
+        public bool IsAuthenticated
         {
-            Credentials = new NetworkCredential(login, pass);
-            page.NavigationService.Navigate(nextUri);
-            page.Dispatcher.BeginInvoke(() => page.NavigationService.RemoveBackEntry());
+            get { 
+                bool authenticated;
+                IsolatedStorageSettings.ApplicationSettings.TryGetValue<bool>("authenticated", out authenticated);
+                return authenticated;
+            }
+            set { IsolatedStorageSettings.ApplicationSettings["authenticated"] = value; }
         }
-
+        
         public void SignOut(Page page)
         {
-            Credentials = null;
+            IsAuthenticated = false;
             page.NavigationService.Navigate(new Uri("/LoginView.xaml", UriKind.Relative));
             page.Dispatcher.BeginInvoke(() => page.NavigationService.RemoveBackEntry());
         }
diff --git a/Juick/Controls/MessageList.xaml b/Juick/Controls/MessageList.xaml
index 7a7d823..afa6c69 100644
--- a/Juick/Controls/MessageList.xaml
+++ b/Juick/Controls/MessageList.xaml
@@ -14,7 +14,7 @@
     d:DesignHeight="480" d:DesignWidth="480">
 
     <Grid x:Name="LayoutRoot">
-        <toolkit:LongListSelector x:Name="longList" Margin="0, 0, -12, 0"
+        <toolkit:LongListSelector Margin="0, 0, -12, 0"
                  ItemsSource="{Binding Items}" IsFlatList="true">
             <i:Interaction.Triggers>
                 <i:EventTrigger EventName="Link">
diff --git a/Juick/Juick.csproj b/Juick/Juick.csproj
index ebe128c..33fbd5c 100644
--- a/Juick/Juick.csproj
+++ b/Juick/Juick.csproj
@@ -103,9 +103,11 @@
       <DependentUpon>ThreadView.xaml</DependentUpon>
     </Compile>
     <Compile Include="ViewModels\AppViewModel.cs" />
+    <Compile Include="ViewModels\LoginViewModel.cs" />
     <Compile Include="ViewModels\PageViewModel.cs" />
     <Compile Include="ViewModels\PostItem.cs" />
     <Compile Include="ViewModels\ThreadViewModel.cs" />
+    <Compile Include="ViewModels\Validation\DataViewModelBase.cs" />
     <Compile Include="ViewModels\ViewModelBase.cs" />
   </ItemGroup>
   <ItemGroup>
diff --git a/Juick/LoginView.xaml b/Juick/LoginView.xaml
index ad1d70c..004580a 100644
--- a/Juick/LoginView.xaml
+++ b/Juick/LoginView.xaml
@@ -3,15 +3,19 @@
     xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
     xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
     xmlns:phone="clr-namespace:Microsoft.Phone.Controls;assembly=Microsoft.Phone"
-    xmlns:shell="clr-namespace:Microsoft.Phone.Shell;assembly=Microsoft.Phone"
+    xmlns:phoneshell="clr-namespace:Microsoft.Phone.Shell;assembly=Microsoft.Phone"
     xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
     xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
+    xmlns:viewModels="clr-namespace:Juick.ViewModels"
     FontFamily="{StaticResource PhoneFontFamilyNormal}"
     FontSize="{StaticResource PhoneFontSizeNormal}"
     Foreground="{StaticResource PhoneForegroundBrush}"
     SupportedOrientations="Portrait" Orientation="Portrait"
     mc:Ignorable="d" d:DesignHeight="768" d:DesignWidth="480"
-    shell:SystemTray.IsVisible="True" Loaded="PhoneApplicationPage_Loaded">
+    phoneshell:SystemTray.IsVisible="True">
+  <phone:PhoneApplicationPage.DataContext>
+    <viewModels:LoginViewModel />
+  </phone:PhoneApplicationPage.DataContext>
 
     <!--LayoutRoot is the root grid where all page content is placed-->
     <Grid x:Name="LayoutRoot" Background="Transparent">
@@ -28,24 +32,26 @@
 
         <!--ContentPanel - place additional content here-->
         <Grid x:Name="ContentPanel" Grid.Row="1" Margin="12,0,12,0">
-            <TextBlock Height="30" HorizontalAlignment="Left" Margin="37,119,0,0" Name="textBlock1" Text="Username" VerticalAlignment="Top" />
-            <TextBox Height="72" HorizontalAlignment="Left" Margin="25,155,0,0" Name="textBox1" Text="{Binding UserName}" VerticalAlignment="Top" Width="409" />
-            <TextBlock Height="30" HorizontalAlignment="Left" Margin="37,246,0,0" Name="textBlock2" Text="Password" VerticalAlignment="Top" />
-            <Button Content="Sign in" Height="72" HorizontalAlignment="Left" Margin="274,360,0,0" Name="button1" VerticalAlignment="Top" Width="160" Click="button1_Click" />
-            <PasswordBox Height="72" HorizontalAlignment="Left" Password="{Binding Password}" Margin="25,282,0,0" Name="textBox2" VerticalAlignment="Top" Width="409" />
+            <TextBlock Height="30" HorizontalAlignment="Left" Margin="37,119,0,0" Text="Username" VerticalAlignment="Top" />
+            <TextBox Height="72" HorizontalAlignment="Left" Margin="25,155,0,0" Text="{Binding Username, Mode=TwoWay}" VerticalAlignment="Top" Width="409" />
+            <TextBlock Height="30" HorizontalAlignment="Left" Margin="37,246,0,0" Text="Password" VerticalAlignment="Top" />
+            <Button Content="Sign in" Height="72" HorizontalAlignment="Left" Margin="274,360,0,0" 
+                    VerticalAlignment="Top" Width="160" Command="{Binding SignInCommand}" />
+            <PasswordBox Height="72" HorizontalAlignment="Left" Password="{Binding Password, Mode=TwoWay}" 
+                         Margin="25,282,0,0" VerticalAlignment="Top" Width="409" />
         </Grid>
     </Grid>
  
     <!--Sample code showing usage of ApplicationBar-->
     <!--<phone:PhoneApplicationPage.ApplicationBar>
-        <shell:ApplicationBar IsVisible="True" IsMenuEnabled="True">
-            <shell:ApplicationBarIconButton IconUri="/Images/appbar_button1.png" Text="Button 1"/>
-            <shell:ApplicationBarIconButton IconUri="/Images/appbar_button2.png" Text="Button 2"/>
-            <shell:ApplicationBar.MenuItems>
-                <shell:ApplicationBarMenuItem Text="MenuItem 1"/>
-                <shell:ApplicationBarMenuItem Text="MenuItem 2"/>
-            </shell:ApplicationBar.MenuItems>
-        </shell:ApplicationBar>
+        <phoneshell:ApplicationBar IsVisible="True" IsMenuEnabled="True">
+            <phoneshell:ApplicationBarIconButton IconUri="/Images/appbar_button1.png" Text="Button 1"/>
+            <phoneshell:ApplicationBarIconButton IconUri="/Images/appbar_button2.png" Text="Button 2"/>
+            <phoneshell:ApplicationBar.MenuItems>
+                <phoneshell:ApplicationBarMenuItem Text="MenuItem 1"/>
+                <phoneshell:ApplicationBarMenuItem Text="MenuItem 2"/>
+            </phoneshell:ApplicationBar.MenuItems>
+        </phoneshell:ApplicationBar>
     </phone:PhoneApplicationPage.ApplicationBar>-->
 
 </phone:PhoneApplicationPage>
diff --git a/Juick/LoginView.xaml.cs b/Juick/LoginView.xaml.cs
index 098275b..06ac58c 100644
--- a/Juick/LoginView.xaml.cs
+++ b/Juick/LoginView.xaml.cs
@@ -1,5 +1,6 @@
 using System.Linq;
 using System.Windows;
+using Juick.ViewModels;
 using Microsoft.Phone.Controls;
 using System;
 
@@ -10,27 +11,18 @@ namespace Juick
         public LoginView()
         {
             InitializeComponent();
-            DataContext = App.AppContext.Account.Credentials;
+            Loaded += (sender, args) =>
+                          {
+                              while (NavigationService.BackStack.Any())
+                                  NavigationService.RemoveBackEntry();
+                          };
         }
 
-        private Uri nextUri;
-
         protected override void OnNavigatedTo(System.Windows.Navigation.NavigationEventArgs e)
         {
-            nextUri = NavigationContext.QueryString.ContainsKey("FileId")
+            ((LoginViewModel)DataContext).NextUri = NavigationContext.QueryString.ContainsKey("FileId")
                 ? new Uri(string.Format("/NewPostView.xaml?FileId={0}", NavigationContext.QueryString["FileId"]), UriKind.Relative)
                 : new Uri("/MainPage.xaml", UriKind.Relative);
         }
-
-        private void button1_Click(object sender, RoutedEventArgs e)
-        {
-            App.AppContext.Account.SignIn(this, textBox1.Text, textBox2.Password, nextUri);
-        }
-
-        private void PhoneApplicationPage_Loaded(object sender, RoutedEventArgs e)
-        {
-            while (NavigationService.BackStack.Any())
-                NavigationService.RemoveBackEntry();
-        }
     }
 }
\ No newline at end of file
diff --git a/Juick/MainPage.xaml b/Juick/MainPage.xaml
index 2e40d0f..45e1ff9 100644
--- a/Juick/MainPage.xaml
+++ b/Juick/MainPage.xaml
@@ -22,14 +22,19 @@
             <RowDefinition Height="*" />
         </Grid.RowDefinitions>
         
-        <controls:Pivot Title="juick" Grid.Row="1">
-            <controls:PivotItem Header="My feed" Margin="0, -5, 0, 0">
-                <usercontrols:MessageList x:Name="Home" />
-            </controls:PivotItem>
-            <controls:PivotItem Header="Last" Margin="0, -5, 0, 0">
-                <usercontrols:MessageList x:Name="Last"/>
-            </controls:PivotItem>            
+        <controls:Pivot x:Name="Pages" Title="juick" Grid.Row="1" ItemsSource="{Binding Pages}">
+          <controls:Pivot.HeaderTemplate>
+            <DataTemplate>
+              <TextBlock Text="{Binding Caption}"></TextBlock>
+            </DataTemplate>
+          </controls:Pivot.HeaderTemplate>
+          <controls:Pivot.ItemTemplate>
+            <DataTemplate>
+              <usercontrols:MessageList />
+            </DataTemplate>
+          </controls:Pivot.ItemTemplate>
         </controls:Pivot>
+        
     </Grid>
     <phone:PhoneApplicationPage.ApplicationBar>
         <phoneshell:ApplicationBar IsVisible="True" IsMenuEnabled="True">
diff --git a/Juick/MainPage.xaml.cs b/Juick/MainPage.xaml.cs
index a634e7f..1c76ee1 100644
--- a/Juick/MainPage.xaml.cs
+++ b/Juick/MainPage.xaml.cs
@@ -4,10 +4,12 @@ using System.Text;
 using System.Windows;
 using System.Windows.Controls;
 using System.Windows.Data;
+using Juick.Controls;
 using Microsoft.Phone.Controls;
 using Microsoft.Phone.Notification;
 using Microsoft.Phone.Shell;
 using Juick.ViewModels;
+using RestSharp;
 
 namespace Juick
 {
@@ -23,7 +25,7 @@ namespace Juick
             //string channelName = "JuickChannel"; // unused variable
 
             InitializeComponent();
-            
+
             /*      // Try to find the push channel.
                   pushChannel = HttpNotificationChannel.Find(channelName);
 
@@ -61,33 +63,32 @@ namespace Juick
 
                   }*/
 
-            // Set the data context of the listbox control to the sample data
             DataContext = App.AppContext;
-            Home.DataContext = ((AppViewModel)DataContext).Pages[0];
-            Last.DataContext = ((AppViewModel)DataContext).Pages[1];
+
             Loaded += (o, args) =>
-            {
-                var progressIndicator = SystemTray.ProgressIndicator;
+                          {
+                              Pages.SelectedIndex = 0;
+                              var progressIndicator = SystemTray.ProgressIndicator;
 
-                if (progressIndicator != null)
-                {
-                    return;
-                }
+                              if (progressIndicator != null)
+                              {
+                                  return;
+                              }
 
-                progressIndicator = new ProgressIndicator();
+                              progressIndicator = new ProgressIndicator();
 
-                SystemTray.SetProgressIndicator(this, progressIndicator);
+                              SystemTray.SetProgressIndicator(this, progressIndicator);
 
-                Binding binding = new Binding("IsDataLoading") { Source = DataContext };
+                              Binding binding = new Binding("IsDataLoading") { Source = DataContext };
 
-                BindingOperations.SetBinding(
-                    progressIndicator, ProgressIndicator.IsVisibleProperty, binding);
+                              BindingOperations.SetBinding(
+                                  progressIndicator, ProgressIndicator.IsVisibleProperty, binding);
 
-                binding = new Binding("IsDataLoading") { Source = DataContext };
+                              binding = new Binding("IsDataLoading") { Source = DataContext };
 
-                BindingOperations.SetBinding(
-                    progressIndicator, ProgressIndicator.IsIndeterminateProperty, binding);
-            };
+                              BindingOperations.SetBinding(
+                                  progressIndicator, ProgressIndicator.IsIndeterminateProperty, binding);
+                          };
         }
 
         protected override void OnNavigatedTo(System.Windows.Navigation.NavigationEventArgs e)
@@ -102,7 +103,7 @@ namespace Juick
             // Ensure that there is at least one key in the query string, and check 
             // whether the "FileId" key is present.
 
-            navigateUri = string.IsNullOrEmpty(App.AppContext.Account.Credentials.UserName) ? loginUriPart : newPostUriPart;
+            navigateUri = App.AppContext.Account.IsAuthenticated ? newPostUriPart : loginUriPart;
             if (queryStrings.ContainsKey("FileId"))
             {
                 FileId = queryStrings["FileId"];
@@ -112,6 +113,11 @@ namespace Juick
             {
                 NavigationService.Navigate(new Uri(navigateUri, UriKind.Relative));
             }
+            App.AppContext.Client.Authenticator = new HttpBasicAuthenticator(App.AppContext.Account.UserName, App.AppContext.Account.Password);
+            if (App.AppContext.Account.IsAuthenticated)
+                foreach (var page in ((AppViewModel)DataContext).Pages)
+                    page.RefreshData();
+            
         }
 
         void PushChannel_ChannelUriUpdated(object sender, NotificationChannelUriEventArgs e)
@@ -163,10 +169,11 @@ namespace Juick
 
         private void ApplicationBarIconButtonClick(object sender, EventArgs e)
         {
-            App.AppContext.Pages[0].Items.Clear();
-            App.AppContext.Pages[1].Items.Clear();
-            App.AppContext.Pages[0].RefreshData();
-            App.AppContext.Pages[1].RefreshData();
+            foreach (var page in App.AppContext.Pages)
+            {
+                page.Items.Clear();
+                page.RefreshData();
+            }
         }
 
         private void ApplicationBarMenuItemClick(object sender, EventArgs e)
diff --git a/Juick/NewPostView.xaml.cs b/Juick/NewPostView.xaml.cs
index 4f3cc06..dbc45c4 100644
--- a/Juick/NewPostView.xaml.cs
+++ b/Juick/NewPostView.xaml.cs
@@ -43,7 +43,7 @@ namespace Juick
             // whether the "FileId" key is present.
             if (queryStrings.ContainsKey("FileId"))
             {
-                App.AppContext.Client.Authenticator = new HttpBasicAuthenticator(App.AppContext.Account.Credentials.UserName, App.AppContext.Account.Credentials.Password);
+                App.AppContext.Client.Authenticator = new HttpBasicAuthenticator(App.AppContext.Account.UserName, App.AppContext.Account.Password);
                 // Retrieve the picture from the media library using the FileID
                 // passed to the application.
                 MediaLibrary library = new MediaLibrary();
diff --git a/Juick/ViewModels/LoginViewModel.cs b/Juick/ViewModels/LoginViewModel.cs
new file mode 100644
index 0000000..95528fe
--- /dev/null
+++ b/Juick/ViewModels/LoginViewModel.cs
@@ -0,0 +1,72 @@
+using System;
+using System.Net;
+using System.Windows;
+using Juick.Classes;
+using Juick.ViewModels.Validation;
+using RestSharp;
+
+namespace Juick.ViewModels
+{
+    public class LoginViewModel : DataViewModelBase 
+    {
+        private string _username;
+        private string _password;
+        private DelegateCommand<RoutedEventArgs> _signInCommand;
+
+        public string Username
+        {
+            get
+            {
+                return _username ?? (_username = App.AppContext.Account.UserName);
+            }
+            set
+            {
+                _username = value;
+                NotifyPropertyChanged("Username");
+            }
+        }
+
+        public string Password
+        {
+            get
+            {
+                return _password ?? (_password = App.AppContext.Account.Password);
+            }
+            set
+            {
+                _password = value;
+                NotifyPropertyChanged("Password");
+            }
+        }
+
+        public Uri NextUri { get; set; }
+
+        public DelegateCommand<RoutedEventArgs> SignInCommand
+        {
+            get
+            {
+                return _signInCommand ?? (_signInCommand = new DelegateCommand<RoutedEventArgs>(CheckAuth, () => true));
+            }
+        }
+
+        public void CheckAuth(RoutedEventArgs e)
+        {
+            App.AppContext.Client.Authenticator = new HttpBasicAuthenticator(Username, Password);
+            App.AppContext.Client.ExecuteAsync(new RestRequest("/post", Method.POST), response =>
+                                                                             {
+                                                                                 if (response.StatusCode ==
+                                                                                     HttpStatusCode.BadRequest)
+                                                                                 {
+                                                                                     App.AppContext.Account.UserName = Username;
+                                                                                     App.AppContext.Account.Password = Password;
+                                                                                     App.AppContext.Account.IsAuthenticated = true;
+                                                                                     ((App)Application.Current).NavigateTo(NextUri, true);
+                                                                                 }
+                                                                                 else
+                                                                                 {
+                                                                                     AddError("Username", "Invalid username or password", false);
+                                                                                 }
+                                                                             });
+        }
+    }
+}
diff --git a/Juick/ViewModels/PageViewModel.cs b/Juick/ViewModels/PageViewModel.cs
index 02f86ff..e398caf 100644
--- a/Juick/ViewModels/PageViewModel.cs
+++ b/Juick/ViewModels/PageViewModel.cs
@@ -31,11 +31,10 @@ namespace Juick.ViewModels
             set
             {
                 _restUri = value;
-                RefreshData();
             }
         }
 
-        public virtual string Caption { get { return "juick"; } }
+        public virtual string Caption { get; set; }
 
         public ObservableCollection<PostItem> Items { get; private set; }
 
@@ -70,7 +69,6 @@ namespace Juick.ViewModels
             }
 
             var request = new RestRequest(requestUri);
-            _context.Client.Authenticator = new HttpBasicAuthenticator(_context.Account.Credentials.UserName, _context.Account.Credentials.Password);
             _context.Client.ExecuteAsync<List<Message>>(request, response =>
             {
                 _context.IsDataLoading = false;
diff --git a/Juick/ViewModels/Validation/DataViewModelBase.cs b/Juick/ViewModels/Validation/DataViewModelBase.cs
new file mode 100644
index 0000000..dcbf34b
--- /dev/null
+++ b/Juick/ViewModels/Validation/DataViewModelBase.cs
@@ -0,0 +1,44 @@
+using System;
+using System.Collections.Generic;
+using System.ComponentModel;
+
+namespace Juick.ViewModels.Validation
+{
+    public class DataViewModelBase : ViewModelBase, IDataErrorInfo
+    {
+
+        private readonly Dictionary<String, List<String>> _errors =
+           new Dictionary<string, List<string>>();
+
+        // Adds the specified error to the errors collection if it is not already 
+        // present, inserting it in the first position if isWarning is false. 
+        public void AddError(string propertyName, string error, bool isWarning)
+        {
+            if (!_errors.ContainsKey(propertyName))
+                _errors[propertyName] = new List<string>();
+
+            if (_errors[propertyName].Contains(error)) return;
+            if (isWarning) _errors[propertyName].Add(error);
+            else _errors[propertyName].Insert(0, error);
+        }
+
+        // Removes the specified error from the errors collection if it is present. 
+        public void RemoveError(string propertyName, string error)
+        {
+            if (!_errors.ContainsKey(propertyName) || !_errors[propertyName].Contains(error)) return;
+            _errors[propertyName].Remove(error);
+            if (_errors[propertyName].Count == 0) _errors.Remove(propertyName);
+        }
+
+        public string Error { get { throw new NotImplementedException(); } }
+
+        public string this[string columnName]
+        {
+            get
+            {
+                return (!_errors.ContainsKey(columnName) ? null :
+                    String.Join(Environment.NewLine, _errors[columnName]));
+            }
+        }
+    }
+}
-- 
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