Getting 'unrecognised selector' from NSNotificationCenter - objective-c

Question

I'm trying to implement an observer in the NSNotificationCenter. Instead of using self as the observer I want to create a little object that does it:
typedef void (^ErrorCallback)(NSError*);
typedef void (^SuccessCallback)();
typedef void (^ReplicationChanged) (NSNotification*);
#interface SyncParams : NSObject
#property (copy) ErrorCallback errorCallback;
#property (copy) SuccessCallback successCallback;
#property (copy) ReplicationChanged replicationChanged;//this used to observe
- (void)replicationChanged:(NSNotification*)notification;
#end
#implementation SyncParams
#end
Then later I create an instance of the observer:
SyncParams* params = [SyncParams alloc];
params.replicationChanged = ^(NSNotification* notification) {
//do stuff here
};
And finally add it to the NSNotificationCenter:
[[NSNotificationCenter defaultCenter] addObserver: params
selector: #selector(replicationChanged:)
name: kCBLReplicationChangeNotification
object: replicationObject];
But I get this error: Exception '-[SyncParams replicationChanged:]: unrecognized selector sent to instance 0x7ff945c049a0' was thrown
I'm very new to objective-c! Any pointers?

Answer 1

Yes and no, I ended up with the following:
[[NSNotificationCenter defaultCenter] addObserverForName:kCBLReplicationChangeNotification object:repl queue:nil usingBlock:^(NSNotification *notification) {
NSString *status;
if (repl.status == kCBLReplicationActive) {
NSLog(#"Repication in progress");
status = #"in-progrss";
} else if (repl.status == kCBLReplicationOffline) {
NSLog(#"Sync in offline");
status = #"offline";
} else if (repl.status == kCBLReplicationStopped) {
NSLog(#"Sync in stopped");
status = #"stopped";
} else if (repl.status == kCBLReplicationIdle) {
NSLog(#"Sync in idle");
status = #"idle";
}
NSError *error = repl.lastError;
if(error) {
status = #"error";
NSLog(#"replication error %#", error.code);
}
NSDictionary *dictionary = #{
#"type": type,
#"changesCount": #(repl.changesCount),
#"completedChangesCount": #(repl.completedChangesCount),
#"running": #(repl.running),
#"status": status,
#"suspended": #(repl.suspended),
};
[self sendEventWithName:#"replicationChanged" body:dictionary];
}];
I only ever get one callback though, when it starts up.