使用Linq MVVM查询ObservableCollection

Question

I want to create a query with linq on my ObservableCollection but it doesn't really work how T tried it.

I have a Model Entry which has {note, information, isActive} as parameters. So I now want to simply just get all the Entries where isActive is true. I don't use it on my dataprovider (once the data gets loaded) because I need to load every entry into the program.

So I thought about to override the getter inside my entries ObservableCollection:

    public ObservableCollection<Note> _entries { get; set; }
    public ObservableCollection<Note> entries
    {
        get
        {
            return new ObservableCollection<Note>(from entry in this._entries
                                                  where entry.isActive == true
                                                  select entry);
        }
        set { this._entries = value; }
    }

But as you might guess this doesn't work.

Regards

Answer 1

Try

        get
        {
            List<Notes> list = _entries.Where(e=>e.isActive).ToList(); 
            return new ObservableCollection<Note>(list) ;
        }

Answer 2

Rather than editing it in the get, try updating the refinedEntries in the entries ' setter. My Linq statement may need work but it encapsulates what I'm trying to suggest.

Essentially keep a copy of everything even the inactive records in entries and another collection to contain only the active records. In this case I'm calling it refinedEntries .

    private ObservableCollection<Note> _entries;

    public ObservableCollection<Note> entries
    {
      get{return _entries;}
      set
      {
        _entries = value;
        RefinedEntries = new ObservableCollection(_entries.Where(e=>e.isActive).Select(e => e));
      }

     }

    public ObservableCollection<Note> refinedEntries {get;set;}

I would also suggest updating refinedEntries when CollectionChangedEvent fires. In this case the only time refinedEntries is updated is when entries is set to a new instance.

When you instantiate an new collection for entries, subscribe to its CollectionChangedEvent . For example if you instantiate the collection in the Model's constructor you could use the following..

entries = new ObservableCollection<Note>();
entries.CollectionChangedEvent += new NotifyCollectionChangedEventHandler((sender,args) => 
{ 
   RefinedEntries = new ObservableCollection(_entries.Where(e=>e.isActive).Select(e => e));
  //Notify the UI that an update has been made.
  OnPropertyChanged("RefinedEntries");
});