public CalculatorViewModel()
{
this.model = new CalculatorModel();
this.CalculateCommand = new MvvmCommand(
param => model.Calculate(),
param => NumberA != 0 && NumberB != 0)
.AddListner <CalculatorViewModel>(this, x => x.NumberA);
}
public CalculatorViewModel(CalculatorModel model)
{
this.model = model;
}