let's see an instance that is easily and  can run well

public class OpenChildWindowCommand : ICommand    {        /// 
        /// 当出现影响是否应执行该命令的更改时发生。        /// 
        public event EventHandler CanExecuteChanged;        /// 
        /// 定义用于确定此命令是否可以在其当前状态下执行的方法。        /// 
        ///         /// 
              public bool CanExecute(object para)        {            if (para != null)            {                CanExecuteChanged(para, new EventArgs());            }            return true;            //return false;        }        /// 
        /// 定义在调用此命令时调用的方法。        /// 
        ///         public void Execute(object para)        {            MessageBox.Show("afdafd");        }     }

and in xaml

and now you click this button you will see the messagebox.

In order to understand the ICommand

let's see it

public interface ICommand    {        // Summary:        //     Occurs when changes occur that affect whether the command should execute.        event EventHandler CanExecuteChanged;        // Summary:        //     Defines the method that determines whether the command can execute in its        //     current state.        //        // Parameters:        //   parameter:        //     Data used by the command. If the command does not require data to be passed,        //     this object can be set to null.        //        // Returns:        //     true if this command can be executed; otherwise, false.        bool CanExecute(object parameter);        //        // Summary:        //     Defines the method to be called when the command is invoked.        //        // Parameters:        //   parameter:        //     Data used by the command. If the command does not require data to be passed,        //     this object can be set to null.        void Execute(object parameter);    }

Now it's clearly

if we want to set the method to the model first we need construct the class like below

public class CommandHandler:ICommand    {        Action

and now in our model class

private ICommand _SaveCommand;        public ICommand SaveCommand        {            get            {                return _SaveCommand = new CommandHandler(Save, _Execute);            }        }        #endregion        private void Save(object param)        {            ObservableCollection
      
        newIM = new ObservableCollection
       
        ();            foreach (Employee e in newIM)            {                string a = e.FirstName;                string b = e.LastName;            }             or othething        }