C# - implementing Concurrent Modifications When Using ObservableCollection in MVVM Pattern
After trying multiple solutions online, I still can't figure this out. I'm working with a question with `ObservableCollection<T>` in my WPF application that follows the MVVM pattern. Specifically, I am trying to update a collection from multiple threads, which I thought would be safe due to the collection's built-in notifications. However, I am running into an `InvalidOperationException` that states "Collection was modified; enumeration operation may not execute." This seems to happen when I try to refresh the UI while the collection is being modified in a background task. Here's a simplified version of my code: ```csharp public class ViewModel : INotifyPropertyChanged { public ObservableCollection<Item> Items { get; set; } public ViewModel() { Items = new ObservableCollection<Item>(); LoadDataAsync(); } private async void LoadDataAsync() { var data = await FetchDataFromApiAsync(); foreach (var item in data) { // This line causes the exception when updating the UI Items.Add(item); } } } ``` I've made sure to call `LoadDataAsync` from the UI thread, but when `Items.Add(item)` is executed, I still get the `InvalidOperationException`. To mitigate this, I tried wrapping the `Items.Add(item)` call in a `Dispatcher.Invoke`, but that just seems to delay the exception until the UI is trying to read the collection during an ongoing modification. ```csharp Application.Current.Dispatcher.Invoke(() => Items.Add(item)); ``` I've also considered using a `lock` around the collection modification, but I’m not sure if that’s appropriate for `ObservableCollection` since it relies on UI notifications, which could be blocked. Is there a best practice to handle this situation, or is there a way to make thread-safe modifications to the `ObservableCollection` while keeping the UI updated? I’m using .NET 5.0 and WPF for this application. Any guidance would be greatly appreciated! For context: I'm using C# on Ubuntu 22.04. Thanks for taking the time to read this!