// After the cell lost the focus, the yearsalary ist set to the new value
        private void datagrid_CellEditEnding(object sender, DataGridCellEditEndingEventArgs e) {
            DataGridColumn col = e.Column;
            e.Cancel = false;

            if (col.Header.Equals("Monthsalary")) {
                DataGridRow row = e.Row;
                ModelEmployee empl = (ModelEmployee)row.Item;
                empl.updateYearsalary();  // important
            }
            System.Diagnostics.Debug.WriteLine("datagrid_CellEditEnding");
        }





In the class

 public void updateYearsalary() {
                NotifyPropertyChanged("Yearsalary");
                System.Diagnostics.Debug.WriteLine("updateYearsalary: " + yearsalary);
 }