Question

I’m trying to load a list of objects as grids with several data and I’ve selected ListBox for it as you can see here:

<ListBox ItemsSource="{Binding People, Mode=TwoWay}" SelectedItem="{Binding Person, Mode=TwoWay}" >
  <ListBox.ItemContainerStyle>
     <Style TargetType="ListBoxItem">
        <Setter Property="HorizontalContentAlignment" Value="Stretch" />
     </Style>
  </ListBox.ItemContainerStyle>
  <ListBox.ItemTemplate>
     <DataTemplate>
         <Grid>
             <Grid.ColumnDefinitions>
                  <ColumnDefinition Width="200"></ColumnDefinition>
                  <ColumnDefinition Width="50"></ColumnDefinition>
                  <ColumnDefinition Width="30"></ColumnDefinition>
                  <ColumnDefinition Width="50"></ColumnDefinition>
                  <ColumnDefinition Width="20"></ColumnDefinition>
             </Grid.ColumnDefinitions>
             <TextBlock VerticalAlignment="Center" Text="{Binding name}" Grid.Column="0" TextAlignment="Right"></TextBlock>
             <TextBox Grid.Column="1" Margin="5,0,0,0" Height="Auto" VerticalAlignment="Center" HorizontalAlignment="Stretch" Text="{Binding age}"></TextBox>
             <TextBlock Grid.Column="2" Text="yo" VerticalAlignment="Center" Margin="5,0,0,0"></TextBlock>
             <TextBox Grid.Column="3" Margin="5,0,0,0" Height="Auto" VerticalAlignment="Center" HorizontalAlignment="Stretch" Text="{Binding baremo}"></TextBox>
             <TextBlock Grid.Column="4" Text="€" VerticalAlignment="Center" Margin="5,0,0,0"></TextBlock>
         </Grid>
    </DataTemplate>
 </ListBox.ItemTemplate>

When I load data into People ObservableCollection everything goes right and it is shown perfectly.

The first time I select a Person, it works and it sets the property value in the VM.

The problem comes the second time I select a different “Person”. The property doesn’t change and… every time I select a different one, it takes a little longer (after 10 ó 20 it is MUCH LONGER).

Here is my ViewModel code:

#region People
        public const string PeoplePropertyName = "People";

        private ObservableCollection<Player> _People;

        public ObservableCollection<Player> People
        {
            get
            {
                return _People;
            }

            set
            {
                _People = value;
                RaisePropertyChanged(People);
            }
        }
        #endregion

        #region Person
        public const string PersonPropertyName = "Person";

        private Player _Person;

        public Player Person
        {
            get
            {
                return _Person;
            }

            set
            {
                _Person = value;
                RaisePropertyChanged(PersonPropertyName);
            }
        }
        #endregion

And I’m loading the People list like this:

void LoadPeople(GetPlayersEventArgs e)
{
     if (this.People == null) this.People = new ObservableCollection<Player>();

        foreach (Player Person in e.Result)
        {
            Player newPerson = new Player();
            ...
            this.People.Add(newPerson);
        }

        this.SetUnBusy();
}

Am I missing anything?? Thanks in advance.

After @Ryan question I’ve seen everytime I try to select another value, I get a lot of:

A first chance exception of type ‘System.InvalidCastException’
occurred in Solution

Answer 1

I’d recommend turning on the feature that will break when a CLR exception is thrown. If you’re using Visual Studio 2010 or 2012, go to Debug -> Exceptions (or Ctrl-E,D by default) and under “Common Language Runtime Exceptions” make sure “Thrown” is checked on. Then re-run your solution and see if anything breaks.

Then you’ll see the problem in your Person object 😉