如何使用不知道何时添加项目的ItemsSource更新Datagrid？

Question

I know I Should implement the INotifyPropertyChanged interface if I want to notify the grid that it should update for the properties in the items, So I did and it was working before.

I decided to change the getter of the bound ObservableCollection so that it would be relative to my DataController class. This way, the Add() method is never called so in theory, the NotifyCollectionChangedEventHandler is never called. Does that sound about right?

This is the grid:

De grid is bound to my TeamQualificationMatches collection residing in the ViewModel :

public ObservableCollection<TeamMatchModel> TeamQualificationMatches
{
    get 
    {
        return new ObservableCollection<TeamMatchModel>(App.Data.GetDoubleTeamMatches().Where(
            match => match.TournamentId == CurrentTournament.Id &&
                     match.Status == MatchStatus.QualificationsPlaying).ToList<TeamMatchModel>());
    }
}

And most of the TeamMatchModel instances implement OnPropertyChanged :

public string Notes
{
    get { return _teamMatch.Notes; }
    set
    {
        _teamMatch.Notes = value;
        OnPropertyChanged("Notes");
    }
}

My logic used to work when my TeamQualificationMatches were as follows:

private ObservableCollection<TeamMatchModel> _teamQualificationMatches = new ObservableCollection<TeamMatchModel>();
public ObservableCollection<TeamMatchModel> TeamQualificationMatches
{
    get
    {
        return _teamQualificationMatches;
    }
}

When I'm changing the status of a TeamMatchModel instance, I do call OnPropertyChanged("TeamQualificationMatches") . So I don't know why the grid doesn't reflect on this update.

public MatchStatus Status
{
    get { return (MatchStatus)_teamMatch.Status; }
    set 
    {
        _teamMatch.Status = (int)value;
        OnPropertyChanged("Status");
        switch (value)
        {
            case MatchStatus.QualificationsPlaying:
                OnPropertyChanged("TeamQualificationMatches");
                break;
            case MatchStatus.PreselectionsPlaying:
                OnPropertyChanged("TeamPreSelectionMatches");
                break;
            case MatchStatus.RoundAPlaying:
                OnPropertyChanged("TeamWinnerMatches");
                break;
            case MatchStatus.RoundBPlaying:
                OnPropertyChanged("TeamLoserMatches");
                break;
        }
    }
}

It must be something simple that I'm overlooking. Any help is appreciated.

Answer 1

You shouldn't bind the UI to a property in the view model that always gives a new value. This is why your original version works. Adding and removing items from the observable collection should update the UI as it implements INotifyCollectionChanged. So keep a single observable collection, bind it to the UI and when you need to just clear it and replace the items.