Observablecollection not updating list, when an item gets added

问题

I'm using the MVVM pattern and want to update a ListView using an observable collection. I went through several SO questions, but cannot see what I'm doing wrong. Any help is much appreciated. Thanks.

View.xaml

Namespace: xmlns:local="clr-namespace:MusicPlayer.ViewModel"

DataContext

<UserControl.DataContext>
    <local:AllTracksViewModel/>
</UserControl.DataContext>

ListView

<ListView x:Name="TrackListView" 
                  ItemsSource="{Binding Path=TrackListObservable}">
...
<ListView.View>
   <GridView>
     <GridViewColumn Header="Title" Width="250" DisplayMemberBinding="{Binding Title}" />
      <GridViewColumn Header="Album" Width="200" DisplayMemberBinding="{Binding Album}" />
      <GridViewColumn Header="Artist" Width="150" DisplayMemberBinding="{Binding Artist}" />
      <GridViewColumn Header="Duration" Width="100" DisplayMemberBinding="{Binding FormattedDuration}" />
      </GridView>
    </ListView.View>
</ListView>

ViewModel.cs

public class AllTracksViewModel
{
    public ObservableCollection<Track> TrackListObservable { get; private set; }

    public AllTracksViewModel()
    {
        TrackListObservable = new ObservableCollection<Track>();
    }
}

I verified that items are definitely getting added to the observable. Again, thanks for the help.

回答1:

Change your code to this:

public class AllTracksViewModel : INotifyPropertyChanged
{
    ObservableCollection<Track> trackListObservable;

    public event PropertyChangedEventHandler PropertyChanged;

    public ObservableCollection<Track> TrackListObservable {
      get { return trackListObservable; }
      set {
        trackListObservable = value;
        if(PropertyChanged!=null) {
          PropertyChanged(this, new PropertyChangedEventArgs("TrackListObservable"));
        }
      }
}

    public AllTracksViewModel()
    {
        TrackListObservable = new ObservableCollection<Track>();
    }
}

Just to explain why: every property of your ViewModel should notify of its changes.

回答2:

You should write this as itemsource

ItemsSource="{Binding ViewModel.TrackListObservable}"

And also set data context of windows to it self.

<Window DataContext="{Binding RelativeSource={RelativeSource Self}}" ...

With this property in MainWindow.

public AllTracksViewModel ViewModel { get; } = new AllTracksViewModel();

Note that you have to add items to this property. ViewModel.TrackListObservable

You should also remove

<UserControl.DataContext>
    <local:AllTracksViewModel/>
</UserControl.DataContext>

since the data context is the main window it self, thats why itemsource is set to ViewModel.TrackListObservable

回答3:

Your code looks correctly. However, I cannot see the method which populates your TrackListObservable. I suggest to you to call a populating method FillData inside of a constructor. Let me show an example:

public class AllTracksViewModel
{
    private ObservableCollection<Track> _trackListObservable;
    public ObservableCollection<Track> TrackListObservable
    {
       get { return _trackListObservable; }
       set { 
             _trackListObservable = value;                 
           }
    }

    public AllTracksViewModel()
    {
         FillData();
    }

    private void FillData()
    {
       _trackListObservable = new ObservableCollection<Track>();
        for (int i = 0; i < 30; i++)
        {
           TrackListObservable.Add(new Track() { Title = "Ben & Joseph " + i.ToString(), 
                                                                 Artist = "Albahari" });
        }   
    }
}

Please, see a work example of binding ListView using MVVM pattern.

回答4:

Here your Property TrackListObservable must be a INotify Property or Dependency Property.So that only you can achieve the result what you want.

Refer the below link regards INotify Property: https://msdn.microsoft.com/library/ms743695(v=vs.100).aspx

来源：https://stackoverflow.com/questions/35975364/observablecollection-not-updating-list-when-an-item-gets-added

标签

wpf

listview

mvvm