为什么此按钮命令绑定不起作用？

Question

I did this like 50 times before. I really don't know why it is not working this time. I have a WPF application and my only dependency is MahApps.Metro. I'm using it's MetroWindow and Dynamic Style on my Button.

Here is the latest xaml:

    <ItemsControl Grid.Column="0" Grid.Row="1" ItemsSource="{Binding ServerList}" Margin="5">
        <ItemsControl.ItemTemplate>
            <DataTemplate>
                <Border Background="LightGray">
                    <StackPanel Orientation="Horizontal">
                        <Button Style="{DynamicResource MetroCircleButtonStyle}" Content="{StaticResource appbar_monitor}" Command="{Binding VM.ServerSelectedCommand, RelativeSource={RelativeSource Mode=FindAncestor, AncestorType=Controls:MetroWindow}}" CommandParameter="{Binding .}"></Button>
                        <Label Content="{Binding .}" HorizontalAlignment="Center" VerticalAlignment="Center"></Label>
                    </StackPanel>
                </Border>
            </DataTemplate>
        </ItemsControl.ItemTemplate>
    </ItemsControl>

Here is my ServerSelectedCommand in my ViewModel:

    private ViewModelCommand _ServerSelectedCommand;
    public ViewModelCommand ServerSelectedCommand
    {
        get
        {
            if (_ServerSelectedCommand == null)
            {
                _ServerSelectedCommand = new ViewModelCommand(
                            p => { SelectServer(p); },
                            p => true
                    );
            }
            return _ServerSelectedCommand;
        }
        set { _ServerSelectedCommand = value; }
    }

    private void SelectServer(object parameter)
    {

    }

ViewModelCommand class is like RelayCommand. Here it is:

public class ViewModelCommand : Observable, ICommand
{
    public bool CanExecuteValue
    {
        get { return CanExecute(null); }
    }
    public ViewModelCommand(
                Action<object> executeAction,
                Predicate<object> canExecute)
    {

        if (executeAction == null)
            throw new ArgumentNullException("executeAction");

        _executeAction = executeAction;
        _canExecute = canExecute;
    }
    private readonly Predicate<object> _canExecute;
    public bool CanExecute(object parameter)
    {
        return _canExecute == null ? true : _canExecute(parameter);
    }
    public event EventHandler CanExecuteChanged;
    public void OnCanExecuteChanged()
    {
        OnPropertyChanged(() => CanExecuteValue);
        if (CanExecuteChanged != null)
            CanExecuteChanged(this, EventArgs.Empty);
    }
    private readonly Action<object> _executeAction;
    public void Execute(object parameter)
    {
        _executeAction(parameter);
    }
}

Sorry for a lot of code. But I need to add them in order to find the problem which I can't see. So lets turn back to first xaml, that is the latest one I tried. Here are the codes that I tried for problematic Button line.

Command="{Binding ServerSelectedCommand, RelativeSource={RelativeSource Mode=FindAncestor, AncestorType=ItemsControl}}"

Command="{Binding ServerSelectedCommand, RelativeSource={RelativeSource Mode=FindAncestor, AncestorType={x:Type local:ViewModel}}}"

This also doesn't provide anything!

Command="{Binding RelativeSource={RelativeSource AncestorType=Controls:MetroWindow}}"

Thanks!

Answer 1

This binding looks like it is looking for ServerSelectedCommand on the ItemsControl:

Command="{Binding ServerSelectedCommand, RelativeSource={RelativeSource Mode=FindAncestor, AncestorType=ItemsControl}}"

try this instead:

Command="{Binding DataContext.ServerSelectedCommand, RelativeSource={RelativeSource Mode=FindAncestor, AncestorType=ItemsControl}}"

Assuming of course that the DataContext of the ItemsControl is your ViewModel.