I posted the following to the .NET CF newsgroup this morning:
The Microsoft.WindowsMobile.Status.SystemState class offers a great way to track a number of interesting and useful device system states (e.g., incoming phone calls, battery strength, etc.). However, recently I observed that the SystemState.Changed += new ChangeEventHandler(OnSystemStateChanged) subscription must be made from the UI thread. Has anyone else run into this? I attempted to write a console app that uses many of these system state notifications; however, none of the events were actually occurring. Once I switched to a form-based application, everything worked great.
Is this documented somewhere? If so, I couldn't find it. I am programming in .NET CF 2 for Windows Mobile 5.0 devices.
Chris Tacke responded with,
Most of those events come from windows messages being posted at a low level (FileSystemWatcher works int he same way too). If you never call Application.Run, no message pump is ever created, so no windows messages are ever dispatched.
I don't think I've ever seen it documented, but if you walk through the aygshell source code in Platform Builder (which a lot of these come from eventually), you'll see that's how they work. I agree that it's a poor choice, but it's how it was implemented. The workaround is a very long, tedious process (again, we've done it for file system notifications) of reimplementing the entire listening system, creating a hidden window for your app or implementing a Run() that doesn't take a Form (like we did in the SDF).
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1 comment:
Hi,
Your app must use a message pump in order to you be able to process any events.
If you don't use any form, you must use Application.DoEvents() instead, as it provides the message pump you need.
-- Manuel Costa
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