MVP after event Binded property null - c#

I am working with WPF MVP. I have a UserControl with DataBinding.
After the user interaction (click event) the property in the presenter is null, but at the next modify on the text when the binding is happening, the customer class not null. I think there is two reference. The datacontext of the view is equal with the presenter.
The datacontext of the view is the presenter.
public class AddCustomerPresenter : PresenterBase<AddCustomerView>
{
private Customer customer;
public Customer Customer
{
get {
return customer ?? new Customer(); }
set
{
customer = value;
RaisePropertyChanged(PropertyName(() => this.Customer));
}
}
/// <summary>
/// todo: a view-khoz lehetne irni egy factoryt
/// </summary>
public AddCustomerPresenter()
{
base.View = new AddCustomerView { DataContext = this};
View.Save += View_Save;
}
void View_Save(object sender, EventArgs e)
{
int a = 2;
}
public void AddToCustomers()
{
new UnitOfWork().CustomerRepository.Add(customer);
}
}
public partial class AddCustomerView : UserControl
{
public event EventHandler Save;
public AddCustomerPresenter Presenter { get { return (AddCustomerPresenter)DataContext; } }
public AddCustomerView()
{
InitializeComponent();
}
private void Save_Click(object sender, RoutedEventArgs e)
{
var handler = Save;
if (handler != null) handler(this, EventArgs.Empty);
}
}
public class Customer : Notifier
{
private string name;
public string Name
{
get { return name; }
set
{
name = value;
RaisePropertyChanged(PropertyName(() => this.Name));
}
}
Address address;
public Address Address
{
get { return address??new Address(); }
set
{
address = value;
RaisePropertyChanged(PropertyName(() => this.Address));
}
}
string phoneNumber;
public string PhoneNumber
{
get { return phoneNumber; }
set
{
phoneNumber = value;
RaisePropertyChanged(PropertyName(() => this.Address));
}
}
}
<UserControl x:Class="RentACar.Views.AddCustomerView"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
mc:Ignorable="d">
<Border BorderBrush="Green" BorderThickness="2">
<DockPanel HorizontalAlignment="Center">
<Label HorizontalAlignment="Center"
Content="asdf"
DockPanel.Dock="Top"
FontSize="34" />
<Grid DataContext="{Binding Customer}" DockPanel.Dock="Top">
<Grid.Resources>
<Style TargetType="Label">
<Setter Property="FontSize" Value="12" />
</Style>
<Style TargetType="TextBox">
<Setter Property="Width" Value="112" />
<Setter Property="HorizontalAlignment" Value="Center" />
</Style>
<Style TargetType="RowDefinition">
<Setter Property="Height" Value="auto" />
</Style>
</Grid.Resources>
<Grid.RowDefinitions>
<RowDefinition />
<RowDefinition />
<RowDefinition />
<RowDefinition />
</Grid.RowDefinitions>
<Grid.ColumnDefinitions>
<ColumnDefinition Width="auto" />
<ColumnDefinition />
</Grid.ColumnDefinitions>
<Label Content=":" />
<TextBox x:Name="asdf"
Grid.Column="1"
Text="{Binding Name}" />
<GroupBox Grid.Row="2"
Grid.ColumnSpan="2"
Header="">
<Grid DataContext="{Binding Address}">
<Grid.RowDefinitions>
<RowDefinition />
<RowDefinition />
<RowDefinition />
</Grid.RowDefinitions>
<Grid.ColumnDefinitions>
<ColumnDefinition Width="auto" />
<ColumnDefinition />
</Grid.ColumnDefinitions>
<Label Content=":" />
<TextBox Grid.Column="1" Text="{Binding City}" />
<Label Grid.Row="1" Content=":" />
<TextBox Grid.Row="1"
Grid.Column="1"
Text="{Binding Street}" />
<Label Grid.Row="2" Content=":" />
<TextBox Grid.Row="2"
Grid.Column="1"
Text="{Binding StreetNumber}" />
</Grid>
</GroupBox>
<Label Grid.Row="3" Content=":" />
<TextBox Grid.Row="3"
Grid.Column="1"
Text="{Binding PhoneNumber}" />
</Grid>
<Button Width="auto"
Margin="0 10 10 10"
HorizontalAlignment="Right"
Click="Save_Click"
Content="" />
</DockPanel>
</Border>
</UserControl>
Demostation:

Problem is in Customer property getter.
return customer ?? new Customer();
it means:
if(customer != null)
{
return customer;
}
else
{
return new Customer();
}
Untill you set customer field you will get new Customer(); every time.
but you probably want something like this.
if(customer != null)
{
return customer;
}
else
{
customer = new Customer();
return customer;
}
or you can simply set that field :) for example in constructor of AddCustomerPresenter and then it's not necessary to have that getter complicated.
it could be:
public Customer Customer
{
get
{
return customer;
}
set
{
customer = value;
RaisePropertyChanged(PropertyName(() => this.Customer));
}
}

Related

CollectionView, DataBinding, MVVM

Hi everyone,
I am trying to implement MVVM in my application but i am failing to load data.
I have a main page and it works fine, but once I want to navigate to the detail of my Ad and then the detail page is blank. There are my controls so i know that the pages is loaded just my data are missing. I cant seem to figure out where i have made the mistake. I am new to coding so i sometimes tend to make very silly mistakes. I been trying to solve this for past few hours otherwise would not post it over here. Thank you of any opinion.
My HomePage
<Grid Grid.Row="1" Margin="0,25,0,0">
<CollectionView x:Name="ads"
ItemsSource="{Binding AdLogEntries}"
ItemTemplate="{StaticResource HomePageTemplate}"
SelectionMode="Single"
SelectedItem="{Binding SelectedAd, Mode=TwoWay}"
SelectionChanged="CollectionView_SelectionChanged"
Margin="12,0">
</CollectionView>
</Grid>
public partial class HomePage : ContentPage
{
public HomePage()
{
InitializeComponent();
BindingContext = new HomePage ViewModel();
}
async void CollectionView_SelectionChanged(object sender, SelectionChangedEventArgs e)
{
var selectedAd = (AdLogEntry)e.CurrentSelection.FirstOrDefault();
if (selectedAd != null)
{
await Navigation.PushAsync(new AdDetail(selectedAd));
}
}
}
namespace Baltazar.ViewModel
{
public class HomePageViewModel : BaseViewModel
{
ObservableCollection<AdLogEntry> _adLogEntries;
public ObservableCollection<AdLogEntry> AdLogEntries { get => _adLogEntries; set { _adLogEntries = value; OnPropertyChanged(); } }
public AdLogEntry selectedAd;
public HomePageViewModel()
{
AdLogEntries = new ObservableCollection<AdLogEntry>()
{
new AdLogEntry (){Id = 0, Image = "cat.jpg", Name = "Kocka" , Description = "seda kocka na prodej, mayliva, hrava, spolecenska " ,Price = 120, },
new AdLogEntry (){Id = 1, Image = "cat2.jpg", Name = "Kocka", Description = "seda kocka na prodej, mayliva, hrava, spolecenska " ,Price = 120, },
new AdLogEntry (){Id = 2, Image = "bobtailjpg.jpg", Name = "Kocka",Description = "seda kocka na prodej, mayliva, hrava, spolecenska ", Price = 120, },
};
}
}
}
//Detail
public class AdDetailViewModel : BaseViewModel
{
AdLogEntry _adDetail;
public AdLogEntry AdDetail { get => _adDetail;set { _adDetail = value;OnPropertyChanged(); } }
public AdDetailViewModel(AdLogEntry adDetail)
{
AdDetail = adDetail;
}
}
public partial class AdDetail : ContentPage
{
//private AdLogEntry selectedAd;
public AdDetail(AdLogEntry adDetail)
{
InitializeComponent();
BindingContext = new AdDetailViewModel(adDetail);
}
}
//BaseViewModel
public class BaseViewModel : INotifyPropertyChanged
{
public event PropertyChangedEventHandler PropertyChanged;
protected BaseViewModel()
{
}
protected virtual void OnPropertyChanged([CallerMemberName]string propertyName = null)
{
PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));
}
}
<Grid>
<Grid.RowDefinitions>
<RowDefinition Height="300" />
<RowDefinition Height="40" />
<RowDefinition Height="*" />
</Grid.RowDefinitions>
<ffimageloading:CachedImage
x:Name="HeaderView"
Grid.Row="0"
Grid.RowSpan="2"
Aspect="AspectFill"
Source="{Binding AdLogEntries.Image}"/>
<controls:Parallax Control
x:Name="Parallax"
Grid.Row="0"
Grid.RowSpan="3">
<Grid>
<Grid.RowDefinitions>
<RowDefinition Height="300" />
<RowDefinition />
</Grid.RowDefinitions>
<yummy:Pancake View
Grid.Row="1"
CornerRadius="24, 24, 0, 0"
BackgroundColor="{StaticResource BackgroundColor}"
Margin="0, 20, 0, 0">
<Grid>
<Grid.RowDefinitions>
<RowDefinition Height="Auto" />
<RowDefinition Height="Auto" />
<RowDefinition Height="Auto" />
<RowDefinition Height="*" />
<RowDefinition Height="Auto" />
</Grid.RowDefinitions>
<!-- Animal NAME -->
<Label
Grid.Row="0"
Text="{Binding AdLogEntries.Name}"
/>
<!-- QUANTITY -->
<Grid
Grid.Row="1">
<Grid.ColumnDefinitions>
<ColumnDefinition Width="Auto" />
<ColumnDefinition Width="*" />
</Grid.ColumnDefinitions>
<Label
Grid.Column="1"
Text="{Binding AdLogEntries.Price, StringFormat='{0:C0}'}"
/>
</Grid>
<!-- ABOUT -->
<Label
Grid.Row="2"
Text="Popis"
/>
<!-- DESCRIPTION -->
<Label
Grid.Row="3"
Text="{Binding AdLogEntries.Description}"
/>
<Grid
Grid.Row="4"
Margin="0, 12">
<Grid.ColumnDefinitions>
<ColumnDefinition Width="80"/>
<ColumnDefinition Width="*" />
</Grid.ColumnDefinitions>
<!-- BUY NOW BUTTON -->
<yummy:PancakeView
Grid.Column="1"
HeightRequest="48"
CornerRadius="24, 0, 24, 0"
Background Color="Accent"
Margin="24, 0, 0, 0">
<Grid>
<Grid.ColumnDefinitions>
<ColumnDefinition Width="30" />
<ColumnDefinition Width="*" />
<ColumnDefinition Width="Auto"/>
</Grid.ColumnDefinitions>
<Label
Grid.Column="1"
Text="Buy now"
/>
<Label
Grid.Column="2"
Text=">"
/>
</Grid>
</yummy:Pancake View>
</Grid>
</Grid>
</yummy:Pancake View>
</Grid>
</controls:Parallax Control>
</Grid>
</ContentPage.Content>
Your SelectedItem never changes because you are not trigger OnPropertyChange. You can change your view model logic like this:
private AdLogEntry selectedAd;
public AdLogEntry SelectedAd { get => selectedAd; set { selectedAd = value; OnPropertyChanged("SelectedAd"); } }
public ICommand AdSelectionChangedCommand => new Command(AdSelectionChanged);
private void AdSelectionChanged()
{
OnPropertyChanged("SelectedAd");
Application.Current.MainPage.Navigation.PushModalAsync(new DetailPage(SelectedAd));
}
And in your XAML:
<CollectionView x:Name="ads"
ItemsSource="{Binding AdLogEntries}"
SelectionMode="Single"
SelectionChangedCommand="{Binding AdSelectionChangedCommand}"
SelectedItem="{Binding SelectedAd, Mode=TwoWay}"
Margin="12,0">
Your detail page:
public DetailPage(AdLogEntry detail)
{
this.BindingContext = new AdDetailViewModel(adDetail);
InitializeComponent();
}
In Detail XAML:
<Label Text="{Binding AdDetail.Name}"/>
your BindingContext is AdDetailViewModel
BindingContext = new AdDetailViewModel(adDetail);
and your binding paths are like
<Label Grid.Row="3" Text="{Binding AdLogEntries.Description}"
AdDetailViewModel does not have a AdLogEntries property. It does have a AdDetail, so presumably you should use this as a binding path
<Label Grid.Row="3" Text="{Binding AdDetail.Description}"
The problem is in your detail page XAML. To be precise, the problem is in your XAML Binding Expressions. All the bindings in the detail page has wrong path set. For example, for image control it should be Source="{Binding AdDetail.Image}" instead of Source="{Binding AdLogEntries.Image}". It happens all the time and you catch these kind of errors in the output log when you debug the application.

Reporting progress from ViewModel method executed in a Task

i'm trying to report progress from ViewModel (MVVM Light) methods that are executed in a task. The ProgressViewModel contains a ProgressModel property that provides properties to describe the current state. Those properties are bound to an Xceed BusyIndicator. So far, so good. But its not working as expected. The ProgressModel.IsRunning is bound to BusyIndiciator.IsBusy and toggles the visibility - that works. ProgressModel.Description and ProgressModel.Percentage are bound to a TextBlock.Text/ProgressBar.Value - but they are not updated...
So... since IsRunning works, whats wrong with Description and Progress...?
// Model
public sealed class ProgressModel: ObservableObject
{
private string m_description;
private float m_percentage;
private bool m_running;
public string Description
{
get { return m_description; }
set { Set(ref m_description, value); }
}
public float Percentage
{
get { return m_percentage; }
set { Set(ref m_percentage, value); }
}
public bool IsRunning
{
get { return m_running; }
set{Set(ref m_running, value);}
}
public void Initiate()
{
Description = string.Empty;
Percentage = 0;
IsRunning = true;
}
}
// Command
private void DownloadWatch()
{
DispatcherHelper.UIDispatcher.Invoke(() =>
{
Progress.Initiate();
});
using (var watch = new PolarWatch())
{
watch.Connect();
for (var i = 0; i < watch.Sessions.Count; i++)
{
DispatcherHelper.UIDispatcher.Invoke(() =>
{
Progress.Description = $"Writing session data for '{session.DateTime}'...";
});
}
}
DispatcherHelper.UIDispatcher.Invoke(() =>
{
Progress.IsRunning = false;
});
}
// View
<xctk:BusyIndicator Name="Busy" IsBusy="{Binding Progress.IsRunning}">
<xctk:BusyIndicator.BusyContentTemplate>
<DataTemplate>
<Grid Width="150">
<Grid.ColumnDefinitions>
<ColumnDefinition Width="*" />
<ColumnDefinition Width="Auto" />
</Grid.ColumnDefinitions>
<Grid.RowDefinitions>
<RowDefinition />
<RowDefinition />
</Grid.RowDefinitions>
<TextBlock Grid.Row="0" Grid.Column="0" Text="{Binding Progress.Description}"/>
<ProgressBar Grid.Row="1" Grid.Column="0" Value="{Binding Progress.Percentage}" Height="14" Margin="0,5,0,0"/>
</Grid>
</DataTemplate>
</xctk:BusyIndicator.BusyContentTemplate>
<xctk:BusyIndicator.ProgressBarStyle>
<Style TargetType="ProgressBar">
<Setter Property="Visibility" Value="Collapsed"/>
</Style>
</xctk:BusyIndicator.ProgressBarStyle>
The DataContext of the root element in the ItemTemplate is not the same as the DataContext of the control itself. Try this:
<TextBlock Grid.Row="0" Grid.Column="0" Text="{Binding DataContext.Progress.Description, RelativeSource={RelativeSource AncestorType=xctk:BusyIndicator}}"/>
<ProgressBar Grid.Row="1" Grid.Column="0" Value="{Binding DataContext.Progress.Percentage,RelativeSource={RelativeSource AncestorType=xctk:BusyIndicator}}" Height="14" Margin="0,5,0,0"/>
Or set the DataContext of the Grid:
<Grid Width="150" DataContext="{Binding DataContext.Progress, RelativeSource={RelativeSource AncestorType=xctk:BusyIndicator}}">
<Grid.ColumnDefinitions>
<ColumnDefinition Width="*" />
<ColumnDefinition Width="Auto" />
</Grid.ColumnDefinitions>
<Grid.RowDefinitions>
<RowDefinition />
<RowDefinition />
</Grid.RowDefinitions>
<TextBlock Grid.Row="0" Grid.Column="0" Text="{Binding Description}"/>
<ProgressBar Grid.Row="1" Grid.Column="0" Value="{Binding Percentage}" Height="14" Margin="0,5,0,0"/>
</Grid>

UI not updating when a property changes

I have the Contact class that implements the INotifyPropertyChanged:
public class Contact : INotifyPropertyChanged
{
public Contact(Contact contact)
{
this.Username = contact.Username;
this.GUID = contact.GUID;
this.Msg = contact.Msg;
this.Ring = contact.Ring;
}
private string username;
public string Username
{
get { return username; }
set
{
username = value;
NotifyPropertyChanged(nameof(Username));
}
}
public Guid GUID { get; set; }
public bool Msg { get; set; }
private bool ring;
public bool Ring
{
get { return ring; }
set
{
ring = value;
NotifyPropertyChanged(nameof(Ring));
}
}
public event PropertyChangedEventHandler PropertyChanged;
public void NotifyPropertyChanged([CallerMemberName] String propertyName = "")
{
PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));
}
}
This is the main page:
public sealed partial class MainPage : Page
{
public ObservableCollection<Contact> Contacts = new ObservableCollection<Contact>();
public MainPage()
{
this.InitializeComponent();
Contacts.Add(new Contact("Contact001", Guid.NewGuid(), false, false));
Contacts.Add(new Contact("Contact002", Guid.NewGuid(), false, false));
}
private void AddContactButton_Click(object sender, RoutedEventArgs e)
{
Contacts.Add(new Contact("ContactN", Guid.NewGuid(), false, false));
}
private void ContactsListView_ItemClick(object sender, ItemClickEventArgs e)
{
Contact clickedContact = (Contact)e.ClickedItem;
int index = Contacts.IndexOf(clickedContact);
Contacts.ElementAt(index).Username = "Qwerty";
}
}
}
This is the XAML:
<Page
x:Class="ContactsListBinding.MainPage"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:local="using:ContactsListBinding"
xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
mc:Ignorable="d"
xmlns:data="using:ContactsListBinding.Models"
xmlns:namespace="ContactsListBinding.Models">
<Page.Resources>
<data:MessageToImageConverter x:Key="MessageToImageConverter" />
<data:RingToImageConverter x:Key="RingToImageConverter" />
</Page.Resources>
<Grid Background="{ThemeResource ApplicationPageBackgroundThemeBrush}">
<Grid.RowDefinitions>
<RowDefinition Height="Auto"/>
<RowDefinition Height="*" />
</Grid.RowDefinitions>
<StackPanel Grid.Row="0" Grid.Column="0">
<Button Name="AddContactButton" Content="Add Contact" Click="AddContactButton_Click" />
<CheckBox Name="MessageMeCheckBox" Content="Message me" />
<CheckBox Name="DeleteMeCheckBox" Content="Delete me" />
</StackPanel>
<ListView Grid.Row="1" Grid.Column="0" Name="ContactsListView"
IsItemClickEnabled="True"
ItemClick="ContactsListView_ItemClick"
ItemsSource="{x:Bind Contacts}">
<ListView.ItemTemplate>
<DataTemplate x:DataType="data:Contact">
<Grid Width="500">
<Grid.RowDefinitions>
<RowDefinition Height="Auto"/>
</Grid.RowDefinitions>
<Grid.ColumnDefinitions>
<ColumnDefinition Width="*" />
<ColumnDefinition Width="Auto" />
<ColumnDefinition Width="Auto" />
</Grid.ColumnDefinitions>
<TextBlock Grid.Row="0" Grid.Column="0" Text="{x:Bind Username}" VerticalAlignment="Center" />
<Image Grid.Row="0" Grid.Column="1" Width="15" Height="15" Source="{x:Bind Msg, Converter={StaticResource MessageToImageConverter}}" />
<Image Grid.Row="0" Grid.Column="2" Width="15" Height="15" Source="{x:Bind Ring, Converter={StaticResource RingToImageConverter}}" />
</Grid>
</DataTemplate>
</ListView.ItemTemplate>
</ListView>
</Grid>
</Page>
So, when I click on an item, I change it's Ring property to true. I have debugged and it is changing to true. The only problem is that my UI isn't updating. Any ideas why?
Okay guys, I finally got it to work. It seems that the Binding Mode should be set to OneWay, instead of the default OneTime. For example the correct xaml should be:
<TextBlock Grid.Row="0" Grid.Column="0" Text="{x:Bind Username, Mode=OneWay}" VerticalAlignment="Center" />
Thank you very much for all your help! :)

WPF Data binding alternate datacontext inside Itemscontrol

What I'm trying to do is bind the controls generated by a ItemsControl.ItemTemplate to a new instance of my ContactInterface class that is created whenever I run my query function.
ContactInterface.cs:
class ContactInterface : INotifyPropertyChanged
{
public string Type { get; set; }
private string firstname;
public string FirstName {
get{return this.firstname;}
set {
if (this.firstname != value) {
this.firstname = value;
this.NotifyPropertyChanged("FirstName");
}
}
}
public event PropertyChangedEventHandler PropertyChanged;
public void NotifyPropertyChanged(string propName)
{
if (this.PropertyChanged != null)
this.PropertyChanged(this, new PropertyChangedEventArgs(propName));
}
}
}
SQL.cs
partial class MainWindow
{
private void selectContact(int? contactID)
{
using (ContactsDataContext context = new ContactsDataContext("Data Source=ds;Initial Catalog=db;Integrated Security=True"))
{
Contact contact = context.Contacts.SingleOrDefault(x => x.ContactID == contactID);
Contact spouse = context.Contacts.SingleOrDefault(x => x.ContactID == contact.Spouse);
Property property = context.Properties.SingleOrDefault(x => x.PropertyID == contact.Address);
ContactInterface selectedContact= new ContactInterface();
selectedContact.FirstName = contact.FirstName;
profileGrid.DataContext = selectedContact;
}
}
MainWindow.xaml
<Grid>
<Grid.ColumnDefinitions>
<ColumnDefinition Width="300" />
<ColumnDefinition Width="*" />
</Grid.ColumnDefinitions>
<ItemsControl Name="Profile_Page_Controls">
<ItemsControl.ItemsPanel>
<ItemsPanelTemplate>
<Grid Margin="15">
<Grid.ColumnDefinitions>
<ColumnDefinition Width="100" />
<ColumnDefinition Width="30" />
<ColumnDefinition Width="100" />
</Grid.ColumnDefinitions>
<Grid.RowDefinitions>
<RowDefinition Height="43" />
<RowDefinition Height="43" />
<RowDefinition Height="43" />
<RowDefinition Height="43" />
<RowDefinition Height="43" />
<RowDefinition Height="43" />
<RowDefinition Height="43" />
<RowDefinition Height="43" />
</Grid.RowDefinitions>
</Grid>
</ItemsPanelTemplate>
</ItemsControl.ItemsPanel>
<ItemsControl.ItemTemplate>
<DataTemplate>
<StackPanel>
<TextBlock Text="{Binding TextContent}"/>
<TextBox Height="23" Text="{Binding Path=FirstName, Mode=TwoWay, UpdateSourceTrigger=PropertyChanged }"/>
</StackPanel>
</DataTemplate>
</ItemsControl.ItemTemplate>
<ItemsControl.ItemContainerStyle>
<Style>
<Setter Property="Grid.Column" Value="{Binding profile_Column}" />
<Setter Property ="Grid.Row" Value="{Binding profile_Row}" />
<Setter Property="Grid.ColumnSpan" Value="{Binding profile_Colspan}" />
</Style>
</ItemsControl.ItemContainerStyle>
</ItemsControl>
<CheckBox Name="profile_SpouseCheck" Grid.Column="1" Margin="0,0,0,0" Checked="profile_SpouseCheck_Checked_1" Unchecked="profile_SpouseCheck_Checked_1"> Spouse</CheckBox>
</Grid>
My plan is to make a new ContactInterface instance every time a user runs the selectContact() function. That new instance will be bound to the generated controls, so when the user makes and saves a change, the textboxes will update that ContactInterface instance and my other functions can grab the data from that ContactInterface to make changes to the database.
Any ideas?

Validating Listbox MVVM

I am using Caliburn.Micro to do convention based binding of the contents of my listbox from a BindableCollection in my ViewModel.
I want to perform Validation on it so that when there is no selection and the user exits the form they get that nice red line around the listbox with the error message that they have to select a value. So far Caliburn has worked great for textbox validation but I can't seem to get it to work on the listbox!
On a side note, is there any way to forcibly run a complete validation from the VM? Currently I am merely doing manual validation by checking the values and changing them so it triggers the Validator which is a bit backwards..
Here is the code for my view:
<UserControl x:Class="AddSessionDialogView"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:toolkit="http://schemas.microsoft.com/winfx/2006/xaml/presentation/toolkit">
<toolkit:BusyIndicator IsBusy="{Binding IsBusy}" BusyContent="{Binding IsBusyStatusDisplay}">
<Grid x:Name="LayoutRoot" Background="White">
<Grid.ColumnDefinitions>
<ColumnDefinition Width="100" />
<ColumnDefinition Width="*" />
</Grid.ColumnDefinitions>
<Grid.RowDefinitions>
<RowDefinition Height="auto"/>
<RowDefinition Height="*"/>
<RowDefinition Height="auto" />
<RowDefinition Height="auto"/>
</Grid.RowDefinitions>
<Grid.Resources>
<Style TargetType="TextBlock">
<Setter Property="Margin" Value="5,9" />
</Style>
<Style TargetType="TextBox">
<Setter Property="Margin" Value="5" />
</Style>
</Grid.Resources>
<TextBlock Text="Session Name" />
<TextBox x:Name="SessionName" Grid.Column="1" />
<TextBlock Text="Scenario" Grid.Row="1" />
<ListBox x:Name="Scenarios" Grid.Row="1" Grid.Column="1" DisplayMemberPath="Name" Margin="5" />
<StackPanel Orientation="Horizontal" HorizontalAlignment="Right" VerticalAlignment="Bottom" Grid.Column="1" Grid.Row="3" Margin="5">
<Button x:Name="Cancel" Height="28" Margin="5" Content="Cancel" Padding="0,2" Width="75" />
<Button x:Name="OK" Height="28" Margin="5" Content="OK" Padding="0,2" Width="100" />
</StackPanel>
</Grid>
</toolkit:BusyIndicator>
Here is the (relevant) code for my viewmodel:
public BindableCollection<Scenario> Scenarios { get; set; }
[Required(ErrorMessage = "You must select a scenario")]
public Scenario SelectedScenario { get; set; }
private string _sessionName;
[Required(ErrorMessage="Session Name is invalid")]
public string SessionName
{
get { return _sessionName; }
set { _sessionName = value; NotifyOfPropertyChange(() => SessionName); }
}
public IEnumerable<IResult> OK()
{
if (SelectedScenario == null)
{
// This forces validation check, but doesnt show validation error on the view!
SelectedScenario = new Scenario();
SelectedScenario = null;
}
if (SessionName == null)
SessionName = "";
if (Validator.TryValidateObject(this, new ValidationContext(this), new List<ValidationResult>()))
{
IsBusy = true;
IsBusyStatusDisplay = "Creating Session...";
yield return new CreateSessionResult(SelectedScenario.Id, SessionName);
IsBusy = false;
yield return Close();
}
}

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