Xamarin Forms ListView ObservableCollection not updating

Question

I have a ListView that is bound to an ObservableCollection composed of viewModels.

the viewModel looks like this:

public string Id{ get; set; }
public string Name{ get; set; }
public bool HasId
{
    get { return !(String.IsNullOrEmpty(Id)); }
}

in the frontend xaml:

<ListView x:Name="MyList" ItemsSource="{Binding MyList}">
  <ListView.ItemTemplate>
    <DataTemplate>
      <ViewCell>
        <StackLayout>
          <Label Text="{Binding Name" FontSize="Small"/>
          <StackLayout Spacing="20">
            <Entry Text="{Binding Id}"/>
            <Button Text="Create Profile" IsEnabled="False">
              <Button.Triggers>
                <DataTrigger TargetType="Button" Binding="{Binding HasId}" Value="True">
                  <Setter Property="IsEnabled" Value="True"/>
                </DataTrigger>
              </Button.Triggers>
            </Button>
          </StackLayout>
        </StackLayout>
      </ViewCell>
    </DataTemplate>
  </ListView.ItemTemplate>
</ListView>

Desired Result: when user types into entry (binded to Id), the button should be enabled.

Actual Result: when user types into entry, nothing happens (I'm guessing cause the ObservableCollection does not see the change within the viewmodel)

Note: When I add/delete an element to/from the ObservableCollection, the view does update (as expected).

Any suggestions/ideas are greatly appreciated!

your ViewModel class needs to implement INotifyPropertyChanged — Jason
@Jason thanks! I didn't understand it the first time I read the documentation, but now it makes sense. — indubitablee

Keith Rome Keith Rome · Accepted Answer · 2016-06-03T21:07:14

You need to implement INotifyPropertyChanged on the viewmodel class.

The ObservableCollection<T> class only handles notifications regarding whether the collection itself has changed - items added/removed/etc. It does not deal with notifications for when properties of the individual items themselves are changed.

Xamarin Forms ListView ObservableCollection not updating

2 Answers