Attached behaviour on parent mvvm doesn't work

Question

I have 2 Usercontrols, parent and child, child control has button witch I want to click with parent viewmodel method, but it doesn't work, please tell me what I miss in parent view, I have something like this:

XAML
...
<view:childUC vm:ChildBehaviuor.AddCommand="{Binding ExampleCommand}"/>

Behavior code:

        public static readonly DependencyProperty AddCommandProperty =DependencyProperty.RegisterAttached
    (
     "AddCommand",
     typeof(ICommand),
     typeof(childBehavior),
     new PropertyMetadata(OnAddCommand)
    );
    public static ICommand GetAddCommand(DependencyObject obj)
    {
        return (ICommand)obj.GetValue(AddCommandProperty);
    }
    public static void SetAddCommand(DependencyObject obj, ICommand value)
    {
        obj.SetValue(AddCommandProperty,value);
    }

private static ICommand command;

private static void OnAddCommand(DependencyObject sender, DependencyPropertyChangedEventArgs e)
        {
            child gp = sender as child;
            childBehavior.command = (ICommand)sender.GetValue(childBehavior.AddCommandProperty);

            if(gp != null && command != null)
            {
                if ((e.NewValue != null) && (e.OldValue == null))
                {
                    gp.AddButton.Click += ButtonClick;
                }
                else if ((e.NewValue == null) && (e.OldValue != null))
                {
                    gp.AddButton.Click -= ButtonClick;
                }
            }
        }
        public static void ButtonClick(object sender,RoutedEventArgs eventArgs)
        {
            childBehavior.command.Execute(null);    
        }

VM parent command:

        public ICommand ExampleCommand
    {
        get
        {
            if (this.exampleCommand == null)
            {
                this.exampleCommand  = new DelegateCommand(...);
            }

            return this.exampleCommand ;
        }
    }

Answer 1

I am not sure if I understood you but if you are looking for a way to execute a command on your child usercontrol when you click a button in your parent usercontrol you need to do following:

1. Let your parent usercontrol implement ICommandSource interface which contains a property called "Command".
2. Bind the certain command which is in your child usercontrol to the "Command" property which you will have available on your parent usercontrol after you implement ICommandSource interface.
3. When you click on your button which is in your parent usercontrol, access inside the button handler, which is a method in your parent usercontrol, the available Command propery that you got though the interface. After accessing the Command property call Command.Execute() method, which will go to your child usercontrol and trigger the command you binded before.

Thats how you execute an command on child usercontrol from parent usercontrol.. if you want it the other way around you just have to replace every child word with parent, and every parent word with child :)