public MyUserControl()
    {
        InitializeComponent();
        DataContext = new YourViewModelClass();
        DependencyPropertyDescriptor dpd = DependencyPropertyDescriptor.FromProperty(Label.ContentProperty, typeof(Label));

        if (dpd != null)
        {
            dpd.AddValueChanged(label, OnLabelContentChanged);
        }
    }
 public PlusCommand(YourViewModelClass vm)
 {
     viewModel = vm;
 }