将项目添加到 ObservableCollection 时出现 InteropServices.COMException

Question

I using signal R core to send me a list of messages but this happen

public ObservableCollection<ChatMessage> Messages { get; set; } = new ObservableCollection<ChatMessage>();

public async void InitSignalRAsync()
    {
        ChatMessage mess = new ChatMessage();
        hubConnection = new HubConnectionBuilder().WithUrl("http://localhost:5000/chatHub").Build();
        await hubConnection.StartAsync();
        hubConnection.On<string, string>("ReceiveMessage", (user, message) =>
        {
            mess.user = user;
            mess.message = message;
            Messages.Add(mess);
        });
    }

I got an error

System.Runtime.InteropServices.COMException:

at my

Messages.Add(mess);

when I receive the data

Answer 1

As Martin noted , you must update ViewModel components from their UI thread.

However, for a solution, I recommend using the more general-purpose SynchronizationContext rather than the UWP-specific Dispatcher class. By using the more general type, your code is more reusable and more testable.

Eg:

public ObservableCollection<ChatMessage> Messages { get; set; } = new ObservableCollection<ChatMessage>();

public async Task InitSignalRAsync()
{
  var context = SynchronizationContext.Current;
  hubConnection = new HubConnectionBuilder().WithUrl("http://localhost:5000/chatHub").Build();
  await hubConnection.StartAsync();
  hubConnection.On<string, string>("ReceiveMessage", (user, message) =>
  {
    var mess = new ChatMessage
    {
      user = user,
      message = message,
    };
    context.Post(_ => Messages.Add(mess));
  });
}

I also changed your async void to async Task (again, better reusability and testability), and made a new ChatMessage for each chat message, which I believe is the intended behavior.

Answer 2

This is happening because the Add() must run on the UI thread when you are using ObservableCollection . So to make it work, make sure to execute the call in Dispatcher.RunAsync() :

Windows.ApplicationModel.Core.CoreApplication.MainView.CoreWindow.Dispatcher.RunAsync(CoreDispatcherPriority.Normal, () => { 
    Messages.Add(mess);
 });