Tracking only the Items in the observableCollection that have changed.Is this possible?

Question

Hi all, I have a datagrid that is bound to a observableCollection of Employees The user is allowed to do in line editing by double clicking the datagridRow. When binding the property in question I also use UpdateSourceTrigger.

When I user presses the save button ,the saveCommand is triggered in my MVVM and I want to create a list of only the employees that I have had property modified.

All my ViewModels implements INotifyPropertyChanged.

Despite lots of links on google I cannot seem to find an example that takes you through or explain how to track the items that have changed in a observablecollection.

Can you help?

Answer 1

Create base class for your Employee, for example, EntityBase and enum describing its states:

    public enum EntityState
    {
        NotChanged,
        Changed,
        Added,
        Deleted
    }

    public abstract class EntityBase : INotifyPropertyChanging, INotifyPropertyChanged
    {
        public event PropertyChangingEventHandler PropertyChanging;
        public event PropertyChangedEventHandler PropertyChanged;

        private EntityState state = EntityState.NotChanged;

        public EntityState State
        {
            get { return state; }
            set { state = value; }
        }

        public EntityBase()
        {
            state = EntityState.NotChanged;
        }

        protected virtual void SendPropertyChanging(string propertyName)
        {
            if ((this.PropertyChanging != null))
            {
                this.PropertyChanging(this, new PropertyChangingEventArgs(propertyName));
            }
        }
        protected virtual void SendPropertyChanged(string propertyName)
        {
            if ((this.PropertyChanged != null))
            {
                this.PropertyChanged(this, new PropertyChangedEventArgs(propertyName));
            }
        }

    }

When one of your employes in collection changed - mark it with EntityState.Changed, and then you can request only changed entities from collection and process them as you want.

Answer 2

I'm not aware of any built in way to do what you want.

What I've done in the past is to implement a boolean IsDirty property on the objects in the collection. Then set the IsDirty property to true anytime you raise PropertyChanged.