Registers anObserver to receive KVO notifications for the specified key-path relative to the receiver.
Original signature is '- (void)addObserver:(NSObject *)anObserver forKeyPath:(NSString *)keyPath options:(NSKeyValueObservingOptions)options context:(void *)context'
Available in Mac OS X v10.3 and later.

C# | Visual Basic | Visual C++ |
void AddObserverForKeyPathOptionsContext( NSObject anObserver, NSString keyPath, NSKeyValueObservingOptions options, IntPtr context )
Sub AddObserverForKeyPathOptionsContext ( _ anObserver As NSObject, _ keyPath As NSString, _ options As NSKeyValueObservingOptions, _ context As IntPtr _ )
void AddObserverForKeyPathOptionsContext( NSObject^ anObserver, NSString^ keyPath, NSKeyValueObservingOptions options, IntPtr context )

- anObserver (NSObject)
- The object to register for KVO notifications. The observer must implement the key-value observing method observeValueForKeyPath:ofObject:change:context:.
- keyPath (NSString)
- The key path, relative to the receiver, of the property to observe. This value must not be nil.
- options (NSKeyValueObservingOptions)
- A combination of the NSKeyValueObservingOptions values that specifies what is included in observation notifications. For possible values, see “NSKeyValueObservingOptions.”
- context (IntPtr)
- Arbitrary data that is passed to anObserver in observeValueForKeyPath:ofObject:change:context:.

- Available in Monobjc Bridge: 10.6 (For Mac OS X 10.6 and later), 10.5 (For Mac OS X 10.5 and later)