Thread: System Messaging puzzle.

Originally Posted by WDT

I am investigating trapping messages by overriding wndproc but I'm now having some problems:

Code:

protected override void WndProc(ref Message m) 
        {        
        // Listen for operating system messages.
            switch (m.Msg)
            {

                case WM_DEVICECHANGE:
                    {                        
                        if (m.WParam.ToInt32() == DBT_DEVICEARRIVAL )//<== Put there to follow the control loop
                            MessageBox.Show("System Device List Changed");                           

                        switch ( dMsg )
                        {
                            case DBT_DEVICEARRIVAL:
                                MessageBox.Show("A device has been docked");
                                break;

                            case DBT_DEVICEREMOVECOMPLETE:
                                MessageBox.Show("A device has been REMOVED");
                                break;

                            default:
                                MessageBox.Show("Unrequired system Message");
                                break;

                        } //end of nested switch statement

                    }
                    break;                                  

            }
            base.WndProc(ref m);
        }//end wndProc

I am trapping the WD_DEVICECHANGE message but not the wParam. I out put the WParam value in my modified code and was getting 7. Can someone tell me why I can't trap the correct wParam?

First of all, the above code doesn't give anyone much to work with as far as solving your problem. There may be a couple of problems. The first is that the OS will only send the WM_DEVICECHANGE message to applications with a top level window. The second is that the OS will send WM_DEVICECHANGE messages on port and volume changes only. To receive notification of other types of device changes you must use RegisterDeviceNotification. This will provide notifications of any type of device interface changes.

Also, you'll have to register a device interface class GUID for every device that you want to support.

If this still does not make any sense, post again, requesting POC code.

DBT_DEVNODES_CHANGED Event

The system broadcasts the DBT_DEVNODES_CHANGED device event when a device has been added to or removed from the system.

That also explains the wParam of 7, since that's its value. The docs list all the valid wParams so use that to explain which other notifications you're getting.

Originally Posted by WDT

Thanks. I was actually already on that path when I posted the message just didn't know how to implement the RegisterDeviceNotification() function properly. doing this allowed me to be able to capture the messages I wanted but I now need an explanation on something else.
Everytime I dock/undock my windows phone I get my message but the default is also triggered twice.

Code:

     protected override void WndProc(ref Message m) 
        {            
        
        // Listen for operating system messages.
            switch (m.Msg)
            {

                case (int)DeviceEvents.deviceEvent:
                    {                        
                        
                        switch ( m.WParam.ToInt32() )
                        {
                            case (int)DeviceEvents.deviceAdded:
                                MessageBox.Show("A device has been docked");
                                break;

                            case (int)DeviceEvents.deviceRemoved:
                                MessageBox.Show("A device has been REMOVED");
                                break;

                            default:
                                MessageBox.Show("unrequired system Message was:\n\t" + m.WParam.ToString());
                                break;

                        } //end of nested switch statement

                    }
                    break;                                  

            }
            base.WndProc(ref m);
        }//end wndProc

The default is capturing the DBT_DEVNODES_CHANGED message or the number 7 if you will. You should at least capture one DBT_DEVNODES_CHANGED message when your device is connected or unconnected. This is for the most part dependent on the GUIDs you have registered.