iphone location method startMonitoringSignificantChanges fails to work

i am developing an application for iphone using iOS 4.2 SDK.

My application need to popup an alert when a user arrives a specific location (in 400m radius). Note that I need to get this alert even if the app is in the background.

When I use the locationManager with startUpdatingLocation mode, 开发者_如何转开发i get the alert when the app is in the foreground, but not when it is in the background.

When I try to run with locationManager with startMonitoringSignificantChanges mode, i don't get any position changes in background and even not in foreground (i.e. didUpdateLocation method is never called. only once in the application start up)

some facts:

1. I updated info.plist with UIBackgroundMode with 'location' as first item in array.

2. I updated info.plist UIDeviceCapabilities with gps and location-services (though it doesn't really matters)

3. all said above refers to running this app on the 3GS iphone device.

4. I tried this app on sdk 4.0 and 4.1 and got the same problem.

5. The device supports startMonitoringSignificantChanges use (method of locationManager confirms it)

6. When I check the app on the device i move in range of ~150 meters meters. Is the startMonitoringSignificantChanges will call didUpdateLocation method with this kind of movement?

7. All settings on the devices are turned to on mode (roaming, 3G, wifi,...)

Am i missing something? any ideas?

Thanks,

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if you're still interested, have a look at that post: Behaviour for significant change location API when terminated/suspended?

and the example project mentioned: http://www.cannonade.net/blog.php?id=1480