Question

I have two ViewModels:

public class CommandViewModel
{
    public string DisplayName { get; set; }
    public ICommand Command { get; set; }
}

and

public class SomeViewModel : INotifyPropertyChanged
{
    private bool someFlag;
    private CommandViewModel someCommand;

    public bool SomeFlag
    {
        get
        {
            return someFlag;
        }
        set
        {
            if (value == someFlag)
                return;
            someFlag = value;
            OnPropertyChanged("SomeFlag");
        }
    }

    public CommandViewModel SomeCommandViewModel
    {
        get
        {
            if (someCommand == null)
            {
                someCommand = new CommandViewModel();
                // TODO: actually set the DisplayName and Command
            }
            return someCommand;
        }
    }
}

And I have two corresponding Views:

<UserControl x:Class="ButtonView"
             xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
             xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
             xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006" 
             xmlns:d="http://schemas.microsoft.com/expression/blend/2008" 
             mc:Ignorable="d" 
             d:DesignHeight="28" d:DesignWidth="91">
    <Button Content="{Binding Path=DisplayName}" Command="{Binding Path=Command}" />
</UserControl>

and

<UserControl x:Class="SomeView"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006" 
    xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
    mc:Ignorable="d" Height="125" Width="293" />

    <ViewButton
        Visibility="{Binding Path=SomeFlag, Converter={StaticResource BoolToVisibilityConverter}}"
        DataContext="{Binding Path=SomeCommandViewModel}" />
</UserControl>

I’m having a problem getting ButtonView’s Visibility bound when its DataContext is also bound. If I leave the DataContext out, the Visibility works just fine (when SomeFlag switches value, the button’s visibility changes with it) – but the display text and command don’t work. If I bind the DataContext, the display text and command work, but the visibility doesn’t. I’m sure it has to do with the fact that when I bind the DataContext to SomeCommandViewModel, it is expecting “SomeFlag” to exist within it. And of course, it doesn’t.

Answer 1

I don’t condone your design, but this will work around your immediate problem:

<UserControl x:Name="root"
    x:Class="SomeView"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006" 
    xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
    mc:Ignorable="d" Height="125" Width="293" />

    <ViewButton
        Visibility="{Binding Path=DataContext.SomeFlag, Converter={StaticResource BoolToVisibilityConverter}, ElementName=root}"
        DataContext="{Binding Path=SomeCommandViewModel}" />
</UserControl>