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copied!<p><strong>WELCOME TO THE MAGICAL WORLD OF MULTITHREADING!!!</strong></p> <p>What's happening is that all of your UI elements (class instances) can only be accessed/updated by the UI thread. I won't go into the details about this thread affinity, but its an important subject and you should check it out.</p> <p>The event where data is coming in on the serial port is happening on a <em>different thread than the UI thread</em>. The UI thread has a message pump that handles windows messages (like mouse clicks etc). Your serial port doesn't send off windows messages. When data comes in on the serial port a completely different thread from your UI thread is used to process that message.</p> <p>So, within your application, the mSerialPort_DataReceived method is executing in a different thread than your UI thread. You can use the Threads debugging window to verify this.</p> <p>When you attempt to update your UI, you are trying to modify a control with thread affinity for the UI thread from a different thread, which throws the exception you've seen.</p> <p>TL;DR: You are trying to modify a UI element outside of the UI thread. Use </p> <pre><code>txtSerialOutput.Dispatcher.Invoke </code></pre> <p>to run your update on the UI thread. <a href="http://msdn.microsoft.com/en-us/library/ms591596(VS.85).aspx" rel="noreferrer">There's an example here on how to do thisin the community content of this page.</a></p> <p>The Dispatcher will Invoke your method on the UI thread (it sends a windows message to the UI saying "Hai guize, run this method kthx"), and your method can then safely update the UI from the UI thread.</p>

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