Problem with nested StackPanels and DataContext inheritance in Silverlight 4

Question

I have a problem with nested StackPanels. If I define StackPanels like in the code below, button binds to command (MVVM and command pattern) but doesn't react on button click (command function is not called). When I put stackPanel4 on second position (below stackPanel3) everything works ok. When I move stackPanel4 on the last position (I have more StackPanels then two inside parent StackPanel), button is not bound and command function is not called. What could be a reason for this behavior? If I set DataContext for stackPanel4 it works ok.

    <StackPanel DataContext="{StaticResource vmUserMasterData}" Grid.Column="1" Height="320" HorizontalAlignment="Left" Margin="4,6,4,0" Name="stackPanel1" VerticalAlignment="Top" Width="491">
        <StackPanel Height="40" Name="stackPanel4" Orientation="Horizontal" Width="440">
            <Button Content="Update User Data" Name="button1" Height="23" Width="440" Command="{Binding Path=UpdateDataCommand}"/>
        </StackPanel>
        <StackPanel Height="31" Name="stackPanel3" Orientation="Horizontal" Width="440">
            <sdk:Label Content="Username" Height="28" Name="label2" Width="74" />
            <TextBox Height="23" Name="textBox2" Width="365" Text="{Binding Username, Mode=OneWay}" />
        </StackPanel>
    </StackPanel>

Answer 1

There must be more to this problem. We have reproduced your setup and the command event fires every time, regardless or the order of the StackPanels (basically as you would expect it to work).

Can you provide any source from your ViewModel (specifically relating to how the command is created/used)? The description of the XAML, for the case that fails, is not clear. Can you provide an exact copy of the Xaml when it fails to fire? It might be a specific combination of panels you have on your machine. One wrong closure and it would fail (e.g. if it fell outside stackPanel1 by accident).

Our reproduction (which works regardless of panel order):

Xaml:

<UserControl.Resources>
    <SilverlightApplication1:ViewModel x:Key="vmUserMasterData"/>
</UserControl.Resources>
    <Grid x:Name="LayoutRoot">
        <StackPanel DataContext="{StaticResource vmUserMasterData}" Grid.Column="1" Height="320" HorizontalAlignment="Left" Margin="4,6,4,0" Name="stackPanel1" VerticalAlignment="Top" Width="491">
            <StackPanel Height="31" Name="stackPanel3" Orientation="Horizontal" Width="440">
                <sdk:Label Content="Username" Height="28" Name="label2" Width="74" />
                <TextBox Height="23" Name="textBox2" Width="365" Text="{Binding Username, Mode=OneWay}" />
            </StackPanel>
        <StackPanel Height="40" Name="stackPanel4" Orientation="Horizontal" Width="440">
            <Button Content="Update User Data" Name="button1" Height="23" Width="440" Command="{Binding Path=UpdateDataCommand}"/>
        </StackPanel>
    </StackPanel>
    </Grid>

ViewModel code:

using System.Windows.Input;
using Microsoft.Practices.Prism.Commands;

namespace SilverlightApplication1
{
    public class ViewModel
    {
        public ICommand UpdateDataCommand { get; set; }
        public string Username { get; set; }

        public ViewModel()
        {
            Username = "Woof!";
            UpdateDataCommand = new DelegateCommand<string>(
                (x) =>
                {
                    int dog = 1;    // breakpoint here
                });
        }
    }
}