How to pass object with NSNotificationCenter - objective-c

Question

I am trying to pass an object from my app delegate to a notification receiver in another class.
I want to pass integer messageTotal. Right now I have:
In Receiver:
- (void) receiveTestNotification:(NSNotification *) notification
{
if ([[notification name] isEqualToString:#"TestNotification"])
NSLog (#"Successfully received the test notification!");
}
- (void)viewDidLoad {
[super viewDidLoad];
[[NSNotificationCenter defaultCenter] addObserver:self selector:#selector(dismissSheet) name:UIApplicationWillResignActiveNotification object:nil];
[[NSNotificationCenter defaultCenter] addObserver:self selector:#selector(receiveTestNotification:) name:#"eRXReceived" object:nil];
In the class that is doing the notification:
[UIApplication sharedApplication].applicationIconBadgeNumber = messageTotal;
[[NSNotificationCenter defaultCenter] postNotificationName:#"eRXReceived" object:self];
But I want to pass the object messageTotal to the other class.

Answer 1

You'll have to use the "userInfo" variant and pass a NSDictionary object that contains the messageTotal integer:
NSDictionary* userInfo = #{#"total": #(messageTotal)};
NSNotificationCenter* nc = [NSNotificationCenter defaultCenter];
[nc postNotificationName:#"eRXReceived" object:self userInfo:userInfo];
On the receiving end you can access the userInfo dictionary as follows:
-(void) receiveTestNotification:(NSNotification*)notification
{
if ([notification.name isEqualToString:#"TestNotification"])
{
NSDictionary* userInfo = notification.userInfo;
NSNumber* total = (NSNumber*)userInfo[#"total"];
NSLog (#"Successfully received test notification! %i", total.intValue);
}
}

Answer 2

Building on the solution provided I thought it might be helpful to show an example passing your own custom data object (which I've referenced here as 'message' as per question).
Class A (sender):
YourDataObject *message = [[YourDataObject alloc] init];
// set your message properties
NSDictionary *dict = [NSDictionary dictionaryWithObject:message forKey:#"message"];
[[NSNotificationCenter defaultCenter] postNotificationName:#"NotificationMessageEvent" object:nil userInfo:dict];
Class B (receiver):
- (void)viewDidLoad
{
[super viewDidLoad];
[[NSNotificationCenter defaultCenter]
addObserver:self selector:#selector(triggerAction:) name:#"NotificationMessageEvent" object:nil];
}
#pragma mark - Notification
-(void) triggerAction:(NSNotification *) notification
{
NSDictionary *dict = notification.userInfo;
YourDataObject *message = [dict valueForKey:#"message"];
if (message != nil) {
// do stuff here with your message data
}
}

Answer 3

Swift 5
func post() {
NotificationCenter.default.post(name: Notification.Name("SomeNotificationName"),
object: nil,
userInfo:["key0": "value", "key1": 1234])
}
func addObservers() {
NotificationCenter.default.addObserver(self,
selector: #selector(someMethod),
name: Notification.Name("SomeNotificationName"),
object: nil)
}
#objc func someMethod(_ notification: Notification) {
let info0 = notification.userInfo?["key0"]
let info1 = notification.userInfo?["key1"]
}
Bonus (that you should definitely do!) :
Replace Notification.Name("SomeNotificationName") with .someNotificationName:
extension Notification.Name {
static let someNotificationName = Notification.Name("SomeNotificationName")
}
Replace "key0" and "key1" with Notification.Key.key0 and Notification.Key.key1:
extension Notification {
enum Key: String {
case key0
case key1
}
}
Why should I definitely do this ? To avoid costly typo errors, enjoy renaming, enjoy find usage etc...

Answer 4

Swift 2 Version
As #Johan Karlsson pointed out... I was doing it wrong. Here's the proper way to send and receive information with NSNotificationCenter.
First, we look at the initializer for postNotificationName:
init(name name: String,
object object: AnyObject?,
userInfo userInfo: [NSObject : AnyObject]?)
source
We'll be passing our information using the userInfo param. The [NSObject : AnyObject] type is a hold-over from Objective-C. So, in Swift land, all we need to do is pass in a Swift dictionary that has keys that are derived from NSObject and values which can be AnyObject.
With that knowledge we create a dictionary which we'll pass into the object parameter:
var userInfo = [String:String]()
userInfo["UserName"] = "Dan"
userInfo["Something"] = "Could be any object including a custom Type."
Then we pass the dictionary into our object parameter.
Sender
NSNotificationCenter.defaultCenter()
.postNotificationName("myCustomId", object: nil, userInfo: userInfo)
Receiver Class
First we need to make sure our class is observing for the notification
override func viewDidLoad() {
super.viewDidLoad()
NSNotificationCenter.defaultCenter().addObserver(self, selector: Selector("btnClicked:"), name: "myCustomId", object: nil)
}
Then we can receive our dictionary:
func btnClicked(notification: NSNotification) {
let userInfo : [String:String!] = notification.userInfo as! [String:String!]
let name = userInfo["UserName"]
print(name)
}

Answer 5

Swift 5.1 Custom Object/Type
// MARK: - NotificationName
// Extending notification name to avoid string errors.
extension Notification.Name {
static let yourNotificationName = Notification.Name("yourNotificationName")
}
// MARK: - CustomObject
class YourCustomObject {
// Any stuffs you would like to set in your custom object as always.
init() {}
}
// MARK: - Notification Sender Class
class NotificatioSenderClass {
// Just grab the content of this function and put it to your function responsible for triggering a notification.
func postNotification(){
// Note: - This is the important part pass your object instance as object parameter.
let yourObjectInstance = YourCustomObject()
NotificationCenter.default.post(name: .yourNotificationName, object: yourObjectInstance)
}
}
// MARK: -Notification Receiver class
class NotificationReceiverClass: UIViewController {
// MARK: - ViewController Lifecycle
override func viewDidLoad() {
super.viewDidLoad()
// Register your notification listener
NotificationCenter.default.addObserver(self, selector: #selector(didReceiveNotificationWithCustomObject), name: .yourNotificationName, object: nil)
}
// MARK: - Helpers
#objc private func didReceiveNotificationWithCustomObject(notification: Notification){
// Important: - Grab your custom object here by casting the notification object.
guard let yourPassedObject = notification.object as? YourCustomObject else {return}
// That's it now you can use your custom object
//
//
}
// MARK: - Deinit
deinit {
// Save your memory by releasing notification listener
NotificationCenter.default.removeObserver(self, name: .yourNotificationName, object: nil)
}
}