如何使用 NSNotificationCenter 传递对象

Question

我试图将一个对象从我的应用程序委托传递到另一个类中的通知接收器。

我想传递整数 messageTotal。现在我有：

在接收器中：

- (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];

在正在执行通知的类中：

[UIApplication sharedApplication].applicationIconBadgeNumber = messageTotal;
[[NSNotificationCenter defaultCenter] postNotificationName:@"eRXReceived" object:self];

但我想将对象 messageTotal 传递给另一个类。

Answer 1

您必须使用“userInfo”变体并传递一个包含 messageTotal 整数的 NSDictionary 对象：

NSDictionary* userInfo = @{@"total": @(messageTotal)};

NSNotificationCenter* nc = [NSNotificationCenter defaultCenter];
[nc postNotificationName:@"eRXReceived" object:self userInfo:userInfo];

在接收端，您可以按如下方式访问 userInfo 字典：

-(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

在提供的解决方案的基础上，我认为展示一个传递您自己的自定义数据对象的示例可能会有所帮助（我在此处根据问题将其引用为“消息”）。

A 类（发送方）：

YourDataObject *message = [[YourDataObject alloc] init];
// set your message properties
NSDictionary *dict = [NSDictionary dictionaryWithObject:message forKey:@"message"];
[[NSNotificationCenter defaultCenter] postNotificationName:@"NotificationMessageEvent" object:nil userInfo:dict];

B 类（接收方）：

- (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（你绝对应该这样做！）：

将 Notification.Name("SomeNotificationName") 替换为 .someNotificationName：

extension Notification.Name {
    static let someNotificationName = Notification.Name("SomeNotificationName")
}

替换 "key0"和 "key1" 与 Notification.Key.key0 和 Notification.Key.key1：

extension Notification {
  enum Key: String {
    case key0
    case key1
  }
}

为什么我一定要这样做？为了避免代价高昂的拼写错误，请享受重命名、享受查找用法等......

Answer 4

Swift 2 版本

正如 @Johan Karlsson 指出的......我做错了。这是使用 NSNotificationCenter 发送和接收信息的正确方法。

首先，我们看一下 postNotificationName 的初始化程序：

init(name name: String,
   object object: AnyObject?,
 userInfo userInfo: [NSObject : AnyObject]?)

source

我们将使用 userInfo 参数传递我们的信息。 [NSObject : AnyObject] 类型是 Objective-C 的继承。因此，在 Swift 领域，我们需要做的就是传入一个 Swift 字典，其中包含从 NSObject 派生的键和可以是 AnyObject 的值。

有了这些知识，我们创建一个字典，将其传递到 object 参数中：

 var userInfo = [String:String]()
 userInfo["UserName"] = "Dan"
 userInfo["Something"] = "Could be any object including a custom Type."

然后我们将字典传递到我们的 object 参数中。

发送者

NSNotificationCenter.defaultCenter()
    .postNotificationName("myCustomId", object: nil, userInfo: userInfo)

接收者类

首先我们需要确保我们的类正在观察通知

override func viewDidLoad() {
    super.viewDidLoad()

    NSNotificationCenter.defaultCenter().addObserver(self, selector: Selector("btnClicked:"), name: "myCustomId", object: nil)   
}
    

然后我们可以接收我们的字典：

func btnClicked(notification: NSNotification) {
   let userInfo : [String:String!] = notification.userInfo as! [String:String!]
   let name = userInfo["UserName"]
   print(name)
}

Answer 5

Swift 5.1 自定义对象/类型

// 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)
    }




}