WPF从不同类中调用的方法更新ListBox项

Question

I have been banging my head against WPF ListBox item binding for hours and am hoping to get some advice. My application has three main elements:

1. A Player class that sends and receives data over a TcpClient .
2. A MainWindow that handles the GUI and exposes methods that Player can call to provide data for updating the UI based on network messages.
3. A UserControl called HostLobby that contains 1) a ListBox called gamesListBox for displaying new games as they are added by clients via Player and 2) UI elements for adding a new game to be broadcast to all clients.

I have confirmed that the "upstream" piece works. You can enter new game information on HostLobby , submit, and it propagates to clients as expected. In addition, clients respond properly to server messages telling them a new game has been added.

The problem is, I cannot get gameListBox to update. I rigged up test buttons on both the HostLobby control and MainWindow to verify that binding is working properly - which it is. I just can't seem to update by passing data from Player . Any ideas what I'm doing wrong?

Relevant code:

Player.cs

public void AddGameToLobby(string name, int mp)
{
    // name and mp are provided by the network message handler and work fine
    WriteToLog("Attempting to add game to host lobby", true);        
    mainWindow.AddGameToLobby(name, mp);    
}

MainWindow.cs

public void AddGameToLobby(string n, int mp)
{
    hostLobby.AddGameToList(n, mp);
}

HostLobby.cs

private MainWindow parent; // used to call an AddGame event when client adds a game
public ObservableCollection<Game> games;
public class Game
{
    public string Name { get; set; }
}
public HostLobby(MainWindow mw)
{
    InitializeComponent();
    parent = mw;
    games = new ObservableCollection<Game>();

    // add some test items - this works. the ListBox updates properly
    games.Add(new Game() { Name = "game1" });
    games.Add(new Game() { Name = "game2" });
    games.Add(new Game() { Name = "game3" });

    gamesListBox.ItemsSource = games;
}
public void AddGameToList(string n, int maxp)
{
    // called to announce a new game added by another client
    // call stack is Player.AddGameToLobby -> MainWindow.AddGameToLobby -> this.AddGameToList
    string msg = String.Format("{0} (0/{1})", n, maxp.ToString());
    games.Add(new Game() { Name = msg });
}

HostLobby.xaml

<Grid>
    <Grid.ColumnDefinitions>
        <ColumnDefinition/>
        <ColumnDefinition/>
    </Grid.ColumnDefinitions>

    <StackPanel Grid.Column="0" Margin="50" Orientation="Vertical" VerticalAlignment="Center">
        <StackPanel Orientation="Horizontal">
            <Label HorizontalContentAlignment="Right" Width="80">Game Name:</Label>
            <TextBox Name="gameNameTextBox" VerticalContentAlignment="Center" Width="200"/>
        </StackPanel>
        <StackPanel Orientation="Horizontal" Margin="0,10,0,0">
            <Label HorizontalContentAlignment="Right" Width="80">Max Players:</Label>
            <TextBox Name="maxPlayersTextBox" VerticalContentAlignment="Center" Width="200"/>
        </StackPanel>
        <Button Name="addGameButton" Click="addGameButton_Click" Margin="0,20,0,0" Width="200" Height="30">Add Game</Button>
    </StackPanel>

    <StackPanel Orientation="Vertical" VerticalAlignment="Center" Margin="50" Grid.Column="1">
        <Label>Current Games</Label>
        <ListBox Name="gamesListBox" MinHeight="200">
            <ListBox.ItemTemplate>
                <DataTemplate>
                    <Grid>
                        <TextBlock Text="{Binding Name}"/>
                    </Grid>
                </DataTemplate>
            </ListBox.ItemTemplate>
        </ListBox>
    </StackPanel>
</Grid>

Answer 1

Your ListBox is not being updated because you're modifying the ObservableCollection on a worker thread, which means that the collection's CollectionChanged event is being raised on the worker thread as well. To remedy this, you need to modify your list on the UI thread. To achieve this, you have a few options, but the first ones that come to mind are:

Using Dispatcher.BeginInvoke

In AddGameToList in HostLobby.cs , put the statement that modifies the list inside a Dispatcher.BeginInvoke :

Application.Current.Dispatcher.BeginInvoke((MethodInvoker)(() => games.Add(new Game() { Name = msg })));

Using BindingOperations.EnableCollectionSynchronization (.NET 4.5 or later)

First, create a lock object as a private member of your HostLobby class. Then, after initializing your ObservableCollection , call the following:

BindingOperations.EnableCollectionSynchronization(games, _yourLockObj);

Then, use the lock whenever you modify the list within HostLobby . So in this instance, you'd want to change the list modification in AddGameToList such that it uses the lock:

lock (_yourLockObj)
{
    games.Add(new Game() { Name = msg });
}

---

The latter seems like a better choice in my opinion, but it is only available if you're using .NET 4.5 or later.