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public static LocalAlloc ( int byteCount ) : |
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/// <summary>
/// Queries the device state.
/// </summary>
/// <returns>Device state information</returns>
public GpsDeviceState GetDeviceState()
{
GpsDeviceState device = null;
// allocate a buffer on the native side. Since the
IntPtr pGpsDevice = Utils.LocalAlloc(GpsDeviceState.GpsDeviceStructureSize);
// GPS_DEVICE structure has arrays of characters, it's easier to just
// write directly into memory rather than create a managed structure with
// the same layout.
Marshal.WriteInt32(pGpsDevice, 1); // write out GPS version of 1
Marshal.WriteInt32(pGpsDevice, 4, GpsDeviceState.GpsDeviceStructureSize); // write out dwSize of structure
int result = GPSGetDeviceState(pGpsDevice);
if (result == 0)
{
// instantiate the GpsDeviceState class passing in the native pointer
device = new GpsDeviceState(pGpsDevice);
}
// free our native memory
Utils.LocalFree(pGpsDevice);
return(device);
}
/// <summary>
/// Method used to listen for native events from the GPS.
/// </summary>
private void WaitForGpsEvents()
{
lock (this)
{
bool listening = true;
// allocate 3 handles worth of memory to pass to WaitForMultipleObjects
IntPtr handles = Utils.LocalAlloc(12);
// write the three handles we are listening for.
Marshal.WriteInt32(handles, 0, stopHandle.ToInt32());
Marshal.WriteInt32(handles, 4, deviceStateChangedHandle.ToInt32());
Marshal.WriteInt32(handles, 8, newLocationHandle.ToInt32());
while (listening)
{
int obj = WaitForMultipleObjects(3, handles, 0, -1);
if (obj != waitFailed)
{
switch (obj)
{
case 0:
// we've been signalled to stop
listening = false;
break;
case 1:
// device state has changed
if (deviceStateChanged != null)
{
deviceStateChanged(this, new DeviceStateChangedEventArgs(GetDeviceState()));
}
break;
case 2:
// location has changed
if (locationChanged != null)
{
locationChanged(this, new LocationChangedEventArgs(GetPosition()));
}
break;
}
}
else
{
System.Diagnostics.Debug.WriteLine("wait failed");
}
}
// free the memory we allocated for the native handles
Utils.LocalFree(handles);
// clear our gpsEventThread so that we can recreate this thread again
// if the events are hooked up again.
gpsEventThread = null;
}
}
/// <summary>
/// Get the position reported by the GPS receiver that is no older than
/// the maxAge passed in
/// </summary>
/// <param name="maxAge">Max age of the gps position data that you want back.
/// If there is no data within the required age, null is returned.
/// if maxAge == TimeSpan.Zero, then the age of the data is ignored</param>
/// <returns>GpsPosition class with all the position details</returns>
public GpsPosition GetPosition(TimeSpan maxAge)
{
GpsPosition gpsPosition = null;
if (Opened)
{
// allocate the necessary memory on the native side. We have a class (GpsPosition) that
// has the same memory layout as its native counterpart
IntPtr ptr = Utils.LocalAlloc(Marshal.SizeOf(typeof(GpsPosition)));
// fill in the required fields
gpsPosition = new GpsPosition();
gpsPosition.dwVersion = 1;
gpsPosition.dwSize = Marshal.SizeOf(typeof(GpsPosition));
// Marshal our data to the native pointer we allocated.
Marshal.StructureToPtr(gpsPosition, ptr, false);
// call native method passing in our native buffer
int result = GPSGetPosition(gpsHandle, ptr, 500000, 0);
if (result == 0)
{
// native call succeeded, marshal native data to our managed data
gpsPosition = (GpsPosition)Marshal.PtrToStructure(ptr, typeof(GpsPosition));
if (maxAge != TimeSpan.Zero)
{
// check to see if the data is recent enough.
if (!gpsPosition.TimeValid || DateTime.Now - maxAge > gpsPosition.Time)
{
gpsPosition = null;
}
}
}
// free our native memory
Utils.LocalFree(ptr);
}
return(gpsPosition);
}
