Question

I have a DataTemplate for ListBoxItem that (should be) fairly simple, and just access via {Binding} the properties of my class.

Below is my class and code that creates a simple (dummy) ItemsSource of the ListBox.

public class ChatMessage
{
    public string Message = "Testing Message";
    public DateTime DateReceived = new DateTime(2011, 07, 16, 14, 00, 05);

    public override string ToString()
    {
        return Message;
    }
}

// ....

// Dummy Data
ObservableCollection<ChatMessage> chatItems = new ObservableCollection<ChatMessage>();
for (int i = 0; i < 20; i++)
    chatItems.Add(new ChatMessage());
lbMessages.ItemsSource = chatItems;

Here’s my DataTemplate..

<DataTemplate x:Key="ChatItemListBox">
    <Grid Width="362">
        <Grid.RowDefinitions>
            <RowDefinition Height="Auto" />
            <RowDefinition Height="26" />
        </Grid.RowDefinitions>
        <TextBlock Text="{Binding Message}" />
        <TextBlock Grid.Row="1"Text="{Binding DateReceived}"/>
    </Grid>
</DataTemplate>

For some reason both TextBlocks are completely empty. However, if I change for example {Binding Message} to just {Binding} it will call ToString and show the message.

I know I must be missing something very simple..

Just in case it matters, the ListBox is defined as below:

<ListBox x:Name="lbMessages" Margin="0,8,0,72" ItemTemplate="{StaticResource ChatItemListBox}"/>

Answer 1

You should use properties, not fields.

public class ChatMessage
{
    public string Message { get; set; }
    public DateTime DateReceived { get; set; }

    public override string ToString()
    {
        return Message;
    }

    public ChatMessage()
    {
        Message = "Testing Message";
        DateReceived = new DateTime(2011, 07, 16, 14, 00, 05);
    }
}

This is because binding is using reflection for non-DependencyProperties, and doesn’t look for fields.

(This advice would solve the problem for WPF, but Silverlight may have some additional quirks.)