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copied!<p>You have to use the <strong>Control.InvokeRequired</strong> property to determine if you are on a background thread. Then you need to invoke your logic that modified your UI via the <strong>Control.Invoke</strong> method to force your UI operations to occur on the main thread. You do this by creating a delegate and passing it to the <strong>Control.Invoke</strong> method. The catch here is you need some object derived from <strong>Control</strong> to call these methods.</p> <p><strong>Edit</strong>: As another user posted, if yo you can wait to the <strong>BackgroundWorker.Completed</strong> event to update your UI then you can subscribe to that event and call your UI code directly. BackgroundWorker_Completed is called on the main app thread. my code assumes you want to do updates during the operation. One alternative to my method is to subscribe to the <strong>BwackgroundWorker.ProgressChanged</strong> event, but I believe you'll need to still call <strong>Invoke</strong> to update your UI in that case.</p> <p>for example</p> <pre><code>public class UpdateController { private UserController _userController; BackgroundWorker backgroundWorker = new BackgroundWorker(); public UpdateController(LoginController loginController, UserController userController) { _userController = userController; loginController.LoginEvent += Update; } public void Update() { // The while loop was unecessary here backgroundWorker.DoWork += new DoWorkEventHandler(backgroundWorker_DoWork); backgroundWorker.RunWorkerAsync(); } public delegate void DoUIWorkHandler(); public void backgroundWorker_DoWork(object sender, DoWorkEventArgs e) { // You must check here if your are executing on a background thread. // UI operations are only allowed on the main application thread if (someControlOnMyForm.InvokeRequired) { // This is how you force your logic to be called on the main // application thread someControlOnMyForm.Invoke(new DoUIWorkHandler(_userController.UpdateUsersOnMap); } else { _userController.UpdateUsersOnMap() } } } </code></pre>

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