How do I add item to a list when I select the item from a listview and click add button in the UI on WPF

See more:

C#

WPF

ListView

Hi everyone!
I'm a newbie so excuse my question if it's too fade or if it's out of place.
any way, In my UI (WPF), i have a ListView that i created containing an observable collection of Type " var Collection = new ObservableCollection<type>" and i have two Buttons "Add" & "Delete" I want to do this:
1- Whenever i select an item from my ListView in the UI(just click on it) , and click the "Add" button, the item is stored in a List called Scenario (var Scenario = new List<type>).
2- Whenever i click the "Delete" button the Scenario list becomes empty.

Any help would be very much appreciated and thank you in advance.

What I have tried:

This is the code in the MainWindowModel, basicly my problem is with

OnSelectChanged()

how can i add the type to the list when it's selected and the button "Add" is pressed?? and is it legitimate to put this logic in

OnSelectChanged()

private Type _newType;
     private bool _isSelected;
     public bool IsSelected
     {
         get { return _isSelected; }
         set
         {
             if (_isSelected != value)
             {
                 _isSelected = value;
                 RaisePropertyChanged(nameof(IsSelected));
                 OnCheckChanged();
             }
         }
     }
     private void OnSelectChanged()
     {
         foreach (var type in Collection)
         {
             //if type is selected and "Add" button is pressed then add the type to the List Scenario

         }
     }
           // I used RelayCommand to create the buttons and the execution
public MainWindowModel()
     {
         DeleteCommand = new RelayCommand(o => DeleteExecute());
         AddCommand = new RelayCommand(o => AddExecute());

     }
public ICommand DeleteCommand
     {
         get;
         private set;
     }
     public ICommand AddCommand
     {
         get;
         private set;
     }

     private void DeleteExecute()
     {
         Scenario.Clear();
     }

     private void AddExecute()
     {

        Scenario.Add(NewType);
     }
public Type NewType
     {
         get { return _newType; }
         set { SetPropertyAndFireEvent(ref _newType, value); }
     }