Multithreading/GPS

[markmcgookin]

Hi,

This is a question re: a mobile development project, however I feel my issue is C# based and not anything to do with the mobile side of thigs, so I will leave this post here (as I feel it'll get a better responce)

Right... here we go:

I have an application based on a MS Sample for using GPS on a PDA. It works fine! (Woohoo!) It is using the Microsoft.WindowsMobile.Samples.Location project classes as it's base. These classes use multithreading

// Create and start thread to listen for GPS events
                gpsEventThread = new System.Threading.Thread(new System.Threading.ThreadStart(WaitForGpsEvents));
                gpsEventThread.Start();
 

which is fine, because in my sample app I just create a new GPS() and then I can talk to it.... However this isn't practical in my full blown app that I want to implement this GPS into, as I don't want to put the reams of GPS code in every form (as I need to log the position of the user at various points, i.e. when forms are loaded) the sample uses a lot of custom event handlers etc for some reason, to pass arguments etc, and this is where I start to get a bit hazey. Basically what i want to do is create a new GPS instance/object when the app is run, and for each other form that is opened talk to this GPS and find out my position. Currently when they are all in the same form the code looks like this

        private EventHandler updateDataHandler;
        Gps gps = new Gps();
        GpsPosition position = null;
        GpsDeviceState device = null;
 
...... 
 
private void menuItem2_Click(object sender, EventArgs e)
        {
            try
            {
                Invoke(updateDataHandler);
            }
 
.......
 
private void Form1_Load(object sender, EventArgs e)
        {
            updateDataHandler = new EventHandler(updateData);
 
            label1.Text = "";
 
            gps.DeviceStateChanged += new DeviceStateChangedEventHandler(gps_DeviceStateChanged);
            gps.LocationChanged += new LocationChangedEventHandler(gps_LocationChanged);
        }
 
        void gps_LocationChanged(object sender, LocationChangedEventArgs args)
        {
            position = args.Position;
        }
 
        void gps_DeviceStateChanged(object sender, DeviceStateChangedEventArgs args)
        {
            device = args.DeviceState;
        }
 
        void updateData(object sender, System.EventArgs args)
        {
            Cursor.Current = Cursors.WaitCursor;
 
            if (gps.Opened)
            {
                string str = "";
 
                if (device != null)
                {
                    str = device.FriendlyName + " " + device.ServiceState + ", " + device.DeviceState + "\n";
                }
                else
                {
                    fullData = false;
                }
 
                if (position != null)
                {
                    if (position.LatitudeValid)
                    {
                        str += "Latitude (DD): \n " + position.Latitude + "\n";
                        str += "Latitude (D,M,S): \n " + position.LongitudeInDegreesMinutesSeconds + "\n";
                        myGPSData.Lattitude = position.Latitude.ToString();
                    }
 

this type of thing goes on and on... now when I just tried to stick all this in a class by itself, it all seemed fine but whenever I tried the "Invoke" method to kick off the event handler, I was told that "Invoke does not exist in the current context" and I really dont know what is going on.

I want my GPS to be started on the login form opening, and be able to pull it's position whenever I want using a method off various forms, and close the GPS on the applcation exiting. So essentially have it running, fully functional in the background.

Sorry for such a long post, but I like to get my point accross clearly, and help with how I should do this?

Cheers,

Mark

[Plater]

That Invoke call that you see is really being mapped to this.Invoke() which probably goes to like form1.Invoke() (Invoke is from the Control object)
It's used like you said to force an event to occur.

If you want a better understanding of it, look up events/delegates in the msdn.

Suffice to say you be able to just call the function when you have your own class for it. It looks like they did that just to make sure it was mutli-threaded?