Question

Using the CoreScanner Driver provided by Motorola, I’m trying to write a small winforms application that uses a barcode scanner. I’m able to interact with the scanner just fine, and properly register a call back for the OnBarcodeEvent(). In this callback, I have a Dialog that opens and displays a screen that the user needs to fill in. Shortly after the dialog is opened (using Show()), the program hangs. If I use ShowDialog(), the dialog works, but the dialog is blocking the OnBarcodeEvent event.

My guess to what is happening, is that since the dialog is getting created on the event thread, there is a race condition occurring when using Show(). Since Show() is non-blocking, the thread continues on after displaying the dialog and then dies out. Meanwhile my dialog just lost it’s parent and locks up? Like i said… my best guess.

How can I remedy the situation? That is, How do I write my dialog so that it can be created within a thread not hang?

Answer 1

I have some experience with Motorola/Symbol Handheld-Devices (MC9090) and I guess the SDK will be similar.

It’s hard to say without seeing the code, but my guesses:

1. your common not-UI thread problem – so make sure you open your dialog using UI thread
2. the native Motorola-driver is crashing – no kidding, this happened a lot to me – in my case (compact-framework on a WinCE device) this would not freeze the program but the scanner will not work/receive any messages before restarting the device

In order to fix this you should seperate the showing/handling of user-dialog away from the event and make sure you call this on the UI-thread (Control.InvokeRequired / Control.Invoke).