Detect when removable storage is unmounted

Question

I am working on an app which should detect events that happen when removable storage is unmounted or forcefully unplugged from the USB. How can I receive these events?

I have seen NSWorkspace for the first possibility of smoothly unmounting the device but this class has methods like -unmountAndEjectDeviceAtPath: to unmount a device. Can someone point me to some sample code that detects unmounted volumes?

Answer 1

A pice of code from HardwareGrowler:

NSWorkspace *workspace = [NSWorkspace sharedWorkspace];
NSNotificationCenter *center = [workspace notificationCenter];

[center addObserver:[VolumeNotifier class] selector:@selector(volumeDidMount:) name:NSWorkspaceDidMountNotification object:nil];
[center addObserver:[VolumeNotifier class] selector:@selector(volumeDidUnmount:) name:NSWorkspaceDidUnmountNotification object:nil];
[center addObserver:[VolumeNotifier class] selector:@selector(volumeWillUnmount:) name:NSWorkspaceWillUnmountNotification object:nil];

You then need to implement the methods to react on the notifications ala

+ (void) volumeDidUnmount:(NSNotification *)aNotification;
{
...
}

For the whole implementation check out http://growl.info/source.php In the Source bundle go to Extras/HardwareGrowler and there check out VolumeNotifier.h/m

UPDATE:

Peters answer is superior to this. Please consider using the Disk Arbitration framework if you come about this problem.