Question

I am using MVVM light in conjunction with EF4 and SQL CE 4, but I am having issues with my observable collection. My application doesn’t neccessarily need to use the mvvm pattern, but since I need the benefits of an observablecollection I have decided to learn how to integrate it. I can successfully link my database of property entitites to my listbox and display them, I can also link some properties of these entities to textboxes, but where I am stuck is when I try to update these properties by typing in the textbox. Here is my xaml code for a textbox and the listbox:

 <TextBox Text="{Binding SaleTitle, ValidatesOnDataErrors=true, Mode=TwoWay}"
  <ListBox Height="424" 
        Margin="24,80,0,0"             
        x:Name="listBoxProperties"
        VerticalAlignment="Top" 
        ItemTemplate="{StaticResource propertySummaryTemplate}"
        IsSynchronizedWithCurrentItem="True"  
        Width="216" BorderThickness="0" Background="{x:Null}"
        FontFamily="Segoe UI" 
        ItemsSource="{Binding PropertyList}"
        SelectedItem="{Binding CurrentProperty, Mode=TwoWay}"
        ScrollViewer.HorizontalScrollBarVisibility="Disabled"
        UseLayoutRounding="True" 
        HorizontalAlignment="Left" 
        ScrollViewer.VerticalScrollBarVisibility="Disabled" >          
    </ListBox>

Here is the code of part of my MainViewModel:

   private string _SaleTitle;
    public string SaleTitle
    {
        get
        {
            if (CurrentProperty != null)
                return CurrentProperty.SaleTitle;
            else
                return "";
        }
        set
        {
            _SaleTitle = value;
            RaisePropertyChanged("SaleTitle");
        }
    }



              private RelayCommand loadCommand;
    public ICommand LoadCommand
    {
        get
        {
            if (loadCommand == null)
                loadCommand = new RelayCommand(() => Load());
            return loadCommand;
        }
    }
    private void Load()
    {
        PropertyList = new ObservableCollection<Property>((from property in entities.Properties.Include("Images")
                                                          select property));
        propertyView = CollectionViewSource.GetDefaultView(PropertyList);
        if (propertyView != null)
            propertyView.CurrentChanged += new System.EventHandler(propertyView_CurrentChanged);
        RaisePropertyChanged("CurrentContact");
        RaisePropertyChanged("SaleTitle");
        RaisePropertyChanged("Address");
        RaisePropertyChanged("AuctioneerName");
        RaisePropertyChanged("AgentName");
        RaisePropertyChanged("Price");
        RaisePropertyChanged("NextBid");
        RaisePropertyChanged("Status");
    }


        void propertyView_CurrentChanged(object sender, System.EventArgs e)
    {
        RaisePropertyChanged("CurrentContact");
        RaisePropertyChanged("SaleTitle");
        RaisePropertyChanged("Address");
        RaisePropertyChanged("AuctioneerName");
        RaisePropertyChanged("AgentName");
        RaisePropertyChanged("Price");
        RaisePropertyChanged("NextBid");
        RaisePropertyChanged("Status");
    }

    private Property _CurrentProperty;
    public Property CurrentProperty
    {
        get
        {
            if (propertyView != null)
                return propertyView.CurrentItem as Property;
            return null;
        }

        set
        {
            _CurrentProperty = value;
            RaisePropertyChanged("CurrentProperty");
        }
    }


     public ObservableCollection<Property> PropertyList
    {
        get
        {
            return propertyList;
        }

        set
        {
            if (propertyList == value)
            {
                return;
            }

            var oldValue = propertyList;
            propertyList = value;

            // Update bindings, no broadcast
            RaisePropertyChanged(PropertiesPropertyName);
        }
    }

    public MainViewModel()
    {
        if (IsInDesignMode)
        {
            // Code runs in Blend --> create design time data.
        }
        else
        {
            // Code runs "for real"
            entities = new Model1Container1();
        }
    }

    ////public override void Cleanup()
    ////{
    ////    // Clean up if needed

    ////    base.Cleanup();
    ////}
}

}

The listbox is populated successfully with the content from current selected item, but when I type in it and click out of it or do anything to lose focus it simply goes back to what was there before.

Answer 1

Take a look at your SaleTitle property definition. It Reads value from CurrentProperty.Saletitle but sets value to local field which is not used anythere.