WPF ObservableCollection and Background Thread Updates: A Thread Safety Guide

WPF's ObservableCollection simplifies data binding, but updating it from background threads requires careful handling of thread safety. This article explains the problem and presents a solution using .NET 4.5 features.

The Challenge: Thread Safety with ObservableCollection

Directly modifying an ObservableCollection from a worker thread throws an exception, because WPF demands that UI thread handles changes to bound collections.

The Solution: .NET 4.5 Synchronization

.NET 4.5 introduces BindingOperations.EnableCollectionSynchronization, simplifying thread synchronization for ObservableCollection. This method, called from the UI thread, handles two crucial aspects:

1. Thread Identification: It identifies the UI thread and directs CollectionChanged events to it.
2. Synchronization Locking: It locks the collection to prevent concurrent access from background threads during modifications.

Cooperative Locking: A Key to Success

While EnableCollectionSynchronization provides significant help, maintaining thread safety requires cooperation. Background threads must acquire the same lock used by EnableCollectionSynchronization before modifying the ObservableCollection. This ensures synchronized access.

Implementation Steps

1. Choose a Locking Mechanism: A simple lock statement or a custom locking mechanism can be used.
2. Enable Synchronization (UI Thread): Call BindingOperations.EnableCollectionSynchronization on the UI thread, providing the collection and your chosen locking mechanism.
3. Lock Before Modification (Worker Threads): On all worker threads, acquire the lock before modifying the ObservableCollection and release it afterwards.

By following this cooperative locking approach, you can safely update your ObservableCollection from background threads, ensuring thread safety and enabling smooth, real-time data display in your WPF applications.