What must be created to block the UI appropriately on a Windows Forms/WPF application prior to .NET 4.5?

In a Windows Forms or WPF application prior to .NET 4.5, a BackgroundWorker instance is the suitable approach to prevent the user interface from freezing while performing time-consuming operations. The BackgroundWorker class provides a simple way to run operations on a separate, dedicated thread. This allows for the UI to remain responsive, as the long-running task is executed outside the UI thread.

The BackgroundWorker supports progress reporting and cancellation, making it easy to manage long-running tasks. It raises events to report progress to the UI, enabling a smoother user experience. When a BackgroundWorker is used, the application can update the UI and respond to user interactions without being blocked by the lengthy operation.

When considering other methods such as creating a custom thread or using a Task instance, while they may also allow background processing, they do not offer the built-in support for handling progress updates and cancellation that BackgroundWorker does. The Worker class is less commonly associated with this specific task management context compared to BackgroundWorker. Therefore, the use of a BackgroundWorker instance stands out as the most appropriate choice for this scenario.