public MainWindow()
 {
     InitializeComponent();
     _vm = new ClientViewModel();
     this.DataContext = _vm;
     _vm.LoadClients();
     _vl = new MaterielViewModel();
     this.DataContext = _vl;
     _vl.LoadMateriels();
     _vn = new SiteViewModel();
     this.DataContext = _vn;
     _vn.LoadSites();
     _vp = new InterventionViewModel();
     this.DataContext = _vp;
     _vp.LoadInterventions();
     WindowStartupLocation = System.Windows.WindowStartupLocation.CenterScreen;
 }