CODEWITHSUNDEEP
c#
Oleg Vazhnev
Oleg Vazhnev

Reputation: 24067

how to send event when Collection is modified?

Sorry I'm newbie in C# and events especially. Why I receive NPE?

class WcfModel : IWcfModel
{
    private List<ConsoleData> _dataList;

    public List<ConsoleData> DataList
    {
        get { return _dataList; }
        set { _dataList = value;
            DataArrived(_dataList);  // NPE
        }
    }

    public event Action<List<ConsoleData>> DataArrived;
}

Upvotes: 0

Views: 95

Answers (3)

Oded
Oded

Reputation: 499062

If no object subscribed to the event (that is the delegate has no subscribers), it will be null. You need to test for that:

    set { 
        _dataList = value;

        var dataDel = DataArrived;
        if(dataDel != null)
            dataDel(_dataList);  
    }

Alternatively, use ObservableCollection<ConsoleData> - it has built in events for changes to the collection.

Upvotes: 3

Setyo N
Setyo N

Reputation: 2103

You should add a null checker for the event as the following codes:

  class WcfModel: IWcfModel
  {
    private List<ConsoleData> _dataList;

    public List<ConsoleData> DataList
    {
      get { return _dataList; }
      set
      {
        _dataList = value;
        if ( DataArrived != null )
          DataArrived ( _dataList );
      }
    }

    public event Action<List<ConsoleData>> DataArrived;
  }

Upvotes: 0

Abdul Munim
Abdul Munim

Reputation: 19217

Rather use ObservableCollection<ConsoleData> which has its own event publisher.

class WcfModel : IWcfModel
{
    private ObservableCollection<ConsoleData> _dataList;

    public WcfModel ()
    {
        _dataList = new ObservableCollection<ConsoleData>();
        _dataList.CollectionChanged += DataArrived

    }
    public ObservableCollection<ConsoleData> DataList
    {
        get { return _dataList; }
    }

    public event Action<object, NotifyCollectionChangedEventArgs> DataArrived;
}

Now whenever you do

wcfModelInstance.DataList.Add(new ConsoleData("hello"));

You will be notified when you subscribe DataArrived event in WcfModel.

Hope this helps.

Upvotes: 1

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