Execute and CanExecute with Delegate

Question

Hi,
I'm trying to create a reactive UI and i have to use Execute and CanExecute to enable/disable buttons.
In my app i have 3 button, validate, refuse and delete.
My problem appear when i use the button delete; i get an error from function CanExecute of button valid. This is a null error.
The button delete is define like this : (he call a setter)
private ICommand _MatinSupprimeCommand = null;
public ICommand MatinSupprimeCommand
get
if (_MatinSupprimeCommand == null)
_MatinSupprimeCommand = new Framework.Windows.DelegateCommand(
() => { // Execute function
TypeCongesMatin = TypeCongesDefaut; //that call a setter of TypeCongesMatin
() => //CanExecute
if (Matin != null)
return true;
return false;
return _MatinSupprimeCommand;
The setter called is defined as following: (Matin variable is delete)
private TypeConges _TypeCongesMatin = null;
public TypeConges TypeCongesMatin
get
return _TypeCongesMatin;
set {
_TypeCongesMatin = value;
if (_TypeCongesMatin.Libcourt.In("P", "WE", "FE"))
if (Matin != null)
DataAccess.EntitiesContext.Context.DeleteObject(Matin);
Matin = null;
RaisePropertyChanged("TypeCongesMatin");
RaisePropertyChanged("TypeCongesMatinSelection");
RaisePropertyChanged("Matin");
RaisePropertyChanged("MatinCouleur");
RaisePropertyChanged("MatinCouleurForeGround");
To finnish my button valid :
private ICommand _MatinValideCommand = null;
public ICommand MatinValideCommand
get
if (_MatinValideCommand == null)
_MatinValideCommand = new Framework.Windows.DelegateCommand(
() => //function to execute
if (Matin != null)
Matin.Status = Presence.StatusDemandeConges.Accepter;
RaisePropertyChanged("MatinCouleur");
RaisePropertyChanged("MatinCouleurForeGround");
() => //Can execute function
if ((Matin != null) && (Matin.Status != Presence.StatusDemandeConges.Accepter)) //When i use my command delete the var Matin is set to null but he conser as non null value and call EstValidant.
return Matin.EstValidant(MainContainerViewModel.Courant.Utilisateur);
return false;
return _MatinValideCommand;
The problem is (Matin != null), in the setter of TypeConges i set matin
to null but in this case he's not consider as null in CanExcute.
If you have any idea.
Edit : I have to give information about the error.
The error is throw by EstValidant.
public bool EstValidant(Personne Validant)
int IDValidant = Validant.ID;
if (this.Personne.MesResponsables.FirstOrDefault(P => P.ID == IDValidant) != null)
return true;
return false;
The error is on Personne.MesResponsables because Personne is null.
Normally the function Validant
should not be
called.
Thanks a lot for all futur answer.
Ps : Sorry for my  terrible english

Answer 1

I set matin to null when i do : MatinSupprimeCommand
i call setter with TypeCongesMatin = TypeCongesDefaut;
I'm doing Matin=null; in the setter of TypeCongeMatin
Matin is defined as following.
private Presence _Matin = null;
public Presence Matin
get { return _Matin; }
set {
if( _Matin != null )
_Matin.PropertyChanged -= MatinDemandeConge_PropertyChangedEventHandler;
_Matin = value;
if (_Matin != null)
_Matin.PropertyChanged += MatinDemandeConge_PropertyChangedEventHandler;
RaisePropertyChanged(this.GetPropertyName(() => Matin));
PropertyChangedEventHandler _MatinDemandeConge_PropertyChangedEventHandler = null;
public PropertyChangedEventHandler MatinDemandeConge_PropertyChangedEventHandler
get
if (_MatinDemandeConge_PropertyChangedEventHandler == null)
_MatinDemandeConge_PropertyChangedEventHandler = new PropertyChangedEventHandler(MatinDemandeConge_PropertyChanged);
return _MatinDemandeConge_PropertyChangedEventHandler;
void MatinDemandeConge_PropertyChanged(object sender, PropertyChangedEventArgs e)
if (e.PropertyName == "CodeStatus")
RaisePropertyChanged(this.GetPropertyName(() => MatinCouleur));
It's little more complicated because i choice a day in calendar via the right click (mouse) and i select a day.
This is a calendar compose by ObservableCollection<Jour>
I load all jours, for each jour set the value of Matin if the personne have something register.
For exemple i
have morning
off on the 01/01/2015, so i set value of matin with this value, else he's set to null.
Depends of the holliday of the guy. By default Matin value is null
I'll try to give more information.
I access to same variable Matin in each CanExecute but one of this command set  him to null and other didn't detect the null value. (it's delegate).
I tried to add copy with Presence matin = Matin; but matin is not null... same problem appear