No visible @interface for 'ViewController' declares the selector 'remoteDisconnected'

[ghost]

I implement code like example

-(void)appClient:(ARDAppClient *)client didChangeState:(ARDAppClientState)state{ 
    switch (state) {
        case kARDAppClientStateConnected:
            NSLog(@"Client connected.");
            break;
        case kARDAppClientStateConnecting:
            NSLog(@"Client connecting.");
            break;
        case kARDAppClientStateDisconnected:
            NSLog(@"Client disconnected.");
            [self remoteDisconnected]; //error
            break;
    }
}

No visible @interface for 'ViewController' declares the selector 'remoteDisconnected'

What is remoteDisconnected method? How I implement this method?

[ghost]

- (void)remoteDisconnected {
    if (self.remoteVideoTrack) [self.remoteVideoTrack removeRenderer:self.remoteView];
    self.remoteVideoTrack = nil;
    [self.remoteView renderFrame:nil];
    [self videoView:self.localView didChangeVideoSize:self.localVideoSize];
}