为什么我的ObservableCollection无法观察？

Question

I have the following element in a user control, as the sole child of the default Grid :

<ListView ItemsSource="{Binding LogCollection}" Name="LogView">
    <ListView.View>
        <GridView>
            <GridView.Columns>
                <GridViewColumn DisplayMemberBinding="{Binding Level}" Header="Level"/>
                <GridViewColumn DisplayMemberBinding="{Binding FormattedMessage}" Width="500" Header="Message"/>
                <GridViewColumn DisplayMemberBinding="{Binding Exception}" Header="Exception"/>
            </GridView.Columns>
        </GridView>
    </ListView.View>
</ListView>

In the code behind, I am handling the following event from a custom NLog Target . I am only handling it so because of an example given to me, a total WPF noob, but it seems OK.

private void EventReceived(LogEventInfo message)
{
    Dispatcher.Invoke(() =>
        {
            if (LogCollection.Count >= 50)
            {
                LogCollection.RemoveAt(LogCollection.Count - 1);
            }
            LogCollection.Add(message);
        });
}

The event fires fine, and the Add call is reach when I step through the code. When I mouse-over LogCollection in the XAML view at execution time, I see a "Count = 1" after the Add call, yet my ListView` remains blissfully unaware it is supposed to be showing me a log event.

OK, OK, the abridged code behind for my user control is:

public partial class LoggingControl : UserControl
{
    public ObservableCollection<LogEventInfo> LogCollection { get; set; }
    public LoggingControl()
    {
        LogCollection = new ObservableCollection<LogEventInfo>();
        InitializeComponent();

        foreach (Target target in LogManager.Configuration.AllTargets)
        {
            var memoryEventTarget = target as MemoryEventTarget;
            if (memoryEventTarget != null)
            {
                memoryEventTarget.EventReceived += EventReceived;
            }
        }
    }

    private void EventReceived(LogEventInfo message)
    {
        Dispatcher.BeginInvoke(new Action(() =>
                    {
                        LogCollection.Add(message);
                    }));
    }
}

Answer 1

As mentioned in comments it seems like binding context for ListView.ItemsSource binding is wrong. DataContext . In your case setting DataContext manually could solve the problem

this.DataContext = this; 

But this needs to be done after LogCollection is created as the property itself does not raise INotifyPropertyChanged.PropertyChanged event.

And to answer why DataContext is not set to self by default is because DataContext is inherited throughout visual tree. So UserControl , as any other FrameworkElement , will by default inherit its DataContext from the element where it was placed.

Another thing worth noting is that there can be only one DataContext value. It will be either inherited from visual tree or set manually in your UserControl . You can use inherited context and still bind to UserControl properties by using either RelativeSource or ElementName bindings.

<UserControl ... x:Name="myUserControl">
    <!--  --->
    <ListView ItemsSource="{Binding LogCollection, ElementName=myUserControl}" Name="LogView">

Answer 2

Are you sure that LogCollection that you are actually adding items is the one that you are binding your grid to? I have created a sample application that has your code but works as expected? Maybe you need to post more of your code.

Here is my sample application .

Maybe your ItemsSource binding is now working at all. Do you see any binding errors in the console? Something similar to "BindingExpression path error: 'LogCollection' property not found on 'object'"