NSNotificationCenter NSNotificationCenter Class

Definition

A notification hub for the application.

[Foundation.Register("NSNotificationCenter", true)]
public class NSNotificationCenter : Foundation.NSObject
type NSNotificationCenter = class
    inherit NSObject
Inheritance
NSNotificationCenterNSNotificationCenter
Attributes

Remarks

The NSNotificationCenter is a hub that is used to listen to broadcast messages and post broadcast messages in an application. The messages that are posted are synchronous.

The NSNotificationCenter.DefaultCenter plays a central role in the application as this is where system notifications are posted for interesting system-level events.

Posting a notification is a synchronous process, which means that invoking one of the Post messages on the notification center will block execution until all of the notification handlers have completed running.

Notifications are posted on the same thread as the calling thread which could have undesired effects. If you need to deliver notifications from a background thread, use the BeginInvokeOnMainThread(Action) method to wrap your posting into a delegate that is invoked on the main thread.

When subscribing to a notification, it is possible to subscribe only to a certain kind of notification by specifying the notification name (or null to listen to all notifications posted to the notification center). It is also possible to subscribe only to notifications issued by a specific object. This can be used to filter the amount of notifications received.

Notifications are usually NSString fields that are hosted in some class, for example the Objective-C UITextViewTextDidChangeNotification is found in the class UITextView as the TextDidChangeNotification. For convenience there are overloads that take C# strings.

To register for notifications, you can use the AddObserver method. We recommend that you use the C# versions of these methods, as you can directly connect delegates, lambdas and methods directly into your code. When you use any of the AddObserver methods in this class that take an Action<NSNotification;> parameter, the AddObserver will return a token. This token is then used as the parameter to RemoveNotification when you want to stop listening to a particular event.


NSObject notificationToken;

void Setup ()
{
    notificationToken = NSNotificationCenter.DefaultCenter.AddObserver (FooBar.ClockNotification, OnClockChange);
}

void OnClockChange (NSNotification notification)
{
    Console.WriteLine ("The ClockNotification message was posted");
}

void Teardown ()
{
    NSNotificationCenter.DefaultCenter.RemoveObserver (notificationToken);
}

Starting with MonoTouch 5.4, calling Dispose on the returned notification token will also remove the observer for you, making the code shorter. For example:


NSObject notificationToken;

void Setup ()
{
    notificationToken = NSNotificationCenter.DefaultCenter.AddObserver (FooBar.ClockNotification, OnClockChange);
}

void OnClockChange (NSNotification notification)
{
    Console.WriteLine ("The ClockNotification message was posted");
}

void Teardown ()
{
    notificationToken.Dispose ();
}

Similarly, if your object implements T:System.IDisposable (including any object derived from NSObject) you MUST call RemoveObservers(IEnumerable<NSObject>) or notificationToken.Dispose() in your Dispose function:


class MyClass : NSObject
{
      private NSObject notificationToken; 

      MyClass()
      { 
         notificationToken = NSNotificationCenter.DefaultCenter.AddObserver(notificationName, NotificationHandler);
      }

      void NotificationHandler(NSNotification notification)
      {
         // ... etc ...
      }

      private bool disposed = false;
      override protected void Dispose(bool disposing)
      {
         if (!disposed)
         {
               if (disposing)
               {
                  notificationToken.Dispose();
               }
               disposed = true;
               base.Dispose();
         }
      }
}

Constructors

NSNotificationCenter() NSNotificationCenter()

Default constructor that initializes a new instance of this class with no parameters.

NSNotificationCenter(IntPtr) NSNotificationCenter(IntPtr)

A constructor used when creating managed representations of unmanaged objects; Called by the runtime.

NSNotificationCenter(NSObjectFlag) NSNotificationCenter(NSObjectFlag)

Constructor to call on derived classes to skip initialization and merely allocate the object.

Properties

Class Class Inherited from NSObject
ClassHandle ClassHandle

The handle for this class.

DebugDescription DebugDescription

A developer-meaningful description of this object.

(Inherited from NSObject)
DefaultCenter DefaultCenter

The default notification center, system notifications and system-level events are posted to this notification center.

Description Description

Description of the object, the Objective-C version of ToString.

(Inherited from NSObject)
Handle Handle

Handle (pointer) to the unmanaged object representation.

(Inherited from NSObject)
IsDirectBinding IsDirectBinding Inherited from NSObject
IsProxy IsProxy Inherited from NSObject
RetainCount RetainCount

Returns the current Objective-C retain count for the object.

(Inherited from NSObject)
Self Self Inherited from NSObject
Superclass Superclass Inherited from NSObject
SuperHandle SuperHandle

Handle used to represent the methods in the base class for this NSObject.

(Inherited from NSObject)
Zone Zone Inherited from NSObject

Methods

AddObserver(NSObject, NSString, NSKeyValueObservingOptions, IntPtr) AddObserver(NSObject, NSString, NSKeyValueObservingOptions, IntPtr)

Registers an object for being observed externally (using NSString keyPath). Observed changes are dispatched to the observer’s object ObserveValue(NSString, NSObject, NSDictionary, IntPtr) method.

(Inherited from NSObject)
AddObserver(NSObject, Selector, NSString, NSObject) AddObserver(NSObject, Selector, NSString, NSObject)

Low-level add-bserver API

AddObserver(NSObject, String, NSKeyValueObservingOptions, IntPtr) AddObserver(NSObject, String, NSKeyValueObservingOptions, IntPtr)

Registers an object for being observed externally (using string keyPath). Observed changes are dispatched to the observer’s object ObserveValue(NSString, NSObject, NSDictionary, IntPtr) method.

(Inherited from NSObject)
AddObserver(NSString, Action<NSNotification>) AddObserver(NSString, Action<NSNotification>)

Adds an observer for the specified notification

AddObserver(NSString, Action<NSNotification>, NSObject) AddObserver(NSString, Action<NSNotification>, NSObject)

Adds an observer for the specified notification

AddObserver(NSString, NSKeyValueObservingOptions, Action<NSObservedChange>) AddObserver(NSString, NSKeyValueObservingOptions, Action<NSObservedChange>)

Registers an object for being observed externally using an arbitrary method.

(Inherited from NSObject)
AddObserver(String, NSKeyValueObservingOptions, Action<NSObservedChange>) AddObserver(String, NSKeyValueObservingOptions, Action<NSObservedChange>)

Registers an object for being observed externally using an arbitrary method.

(Inherited from NSObject)
AddObserver(String, NSObject, NSOperationQueue, Action<NSNotification>) AddObserver(String, NSObject, NSOperationQueue, Action<NSNotification>)
AwakeFromNib() AwakeFromNib()

Called after the object has been loaded from the nib file. Overriders must call base.AwakeFromNib().

(Inherited from NSObject)
BeginInvokeOnMainThread(Action) BeginInvokeOnMainThread(Action) Inherited from NSObject
BeginInvokeOnMainThread(Selector, NSObject) BeginInvokeOnMainThread(Selector, NSObject)

Invokes asynchrously the specified code on the main UI thread.

(Inherited from NSObject)
ConformsToProtocol(IntPtr) ConformsToProtocol(IntPtr)

Invoked to determine if this object implements the specified protocol.

(Inherited from NSObject)
Copy() Copy()

Performs a copy of the underlying Objective-C object.

(Inherited from NSObject)
DangerousAutorelease() DangerousAutorelease() Inherited from NSObject
DangerousRelease() DangerousRelease() Inherited from NSObject
DangerousRetain() DangerousRetain() Inherited from NSObject
DidChange(NSKeyValueChange, NSIndexSet, NSString) DidChange(NSKeyValueChange, NSIndexSet, NSString)

Indicates a change occurred to the indexes for a to-many relationship.

(Inherited from NSObject)
DidChange(NSString, NSKeyValueSetMutationKind, NSSet) DidChange(NSString, NSKeyValueSetMutationKind, NSSet) Inherited from NSObject
DidChangeValue(String) DidChangeValue(String)

Indicates that a change occurred on the specified key.

(Inherited from NSObject)
Dispose() Dispose()

Releases the resources used by the NSObject object.

(Inherited from NSObject)
Dispose(Boolean) Dispose(Boolean)

Releases the resources used by the NSObject object.

(Inherited from NSObject)
DoesNotRecognizeSelector(Selector) DoesNotRecognizeSelector(Selector)

Indicates that this object does not recognize the specified selector.

(Inherited from NSObject)
Equals(NSObject) Equals(NSObject) Inherited from NSObject
Equals(Object) Equals(Object) Inherited from NSObject
GetDictionaryOfValuesFromKeys(NSString[]) GetDictionaryOfValuesFromKeys(NSString[])

Retrieves the values of the specified keys.

(Inherited from NSObject)
GetHashCode() GetHashCode()

Generates a hash code for the current instance.

(Inherited from NSObject)
GetMethodForSelector(Selector) GetMethodForSelector(Selector) Inherited from NSObject
GetNativeField(String) GetNativeField(String) Inherited from NSObject
GetNativeHash() GetNativeHash() Inherited from NSObject
Init() Init() Inherited from NSObject
InitializeHandle(IntPtr) InitializeHandle(IntPtr) Inherited from NSObject
InitializeHandle(IntPtr, String) InitializeHandle(IntPtr, String) Inherited from NSObject
Invoke(Action, Double) Invoke(Action, Double) Inherited from NSObject
Invoke(Action, TimeSpan) Invoke(Action, TimeSpan) Inherited from NSObject
InvokeOnMainThread(Action) InvokeOnMainThread(Action) Inherited from NSObject
InvokeOnMainThread(Selector, NSObject) InvokeOnMainThread(Selector, NSObject)

Invokes synchrously the specified code on the main UI thread.

(Inherited from NSObject)
IsEqual(NSObject) IsEqual(NSObject) Inherited from NSObject
IsKindOfClass(Class) IsKindOfClass(Class) Inherited from NSObject
IsMemberOfClass(Class) IsMemberOfClass(Class) Inherited from NSObject
MarkDirty() MarkDirty()

Promotes a regular peer object (IsDirectBinding is true) into a toggleref object.

(Inherited from NSObject)
MutableCopy() MutableCopy()

Creates a mutable copy of the specified NSObject.

(Inherited from NSObject)
ObserveValue(NSString, NSObject, NSDictionary, IntPtr) ObserveValue(NSString, NSObject, NSDictionary, IntPtr)

Indicates that the value at the specified keyPath relative to this object has changed.

(Inherited from NSObject)
PerformSelector(Selector) PerformSelector(Selector) Inherited from NSObject
PerformSelector(Selector, NSObject) PerformSelector(Selector, NSObject) Inherited from NSObject
PerformSelector(Selector, NSObject, Double) PerformSelector(Selector, NSObject, Double)

Invokes the selector on the current instance and if the obj is not null, it passes this as its single parameter.

(Inherited from NSObject)
PerformSelector(Selector, NSObject, Double, NSString[]) PerformSelector(Selector, NSObject, Double, NSString[]) Inherited from NSObject
PerformSelector(Selector, NSObject, NSObject) PerformSelector(Selector, NSObject, NSObject) Inherited from NSObject
PerformSelector(Selector, NSThread, NSObject, Boolean) PerformSelector(Selector, NSThread, NSObject, Boolean) Inherited from NSObject
PerformSelector(Selector, NSThread, NSObject, Boolean, NSString[]) PerformSelector(Selector, NSThread, NSObject, Boolean, NSString[]) Inherited from NSObject
PostNotification(NSNotification) PostNotification(NSNotification)

Posts a notification that is broadcast to everyoned subscribing to that notification.

PostNotificationName(String, NSObject) PostNotificationName(String, NSObject)
PostNotificationName(String, NSObject, NSDictionary) PostNotificationName(String, NSObject, NSDictionary)
PrepareForInterfaceBuilder() PrepareForInterfaceBuilder() Inherited from NSObject
RemoveObserver(NSObject) RemoveObserver(NSObject)
RemoveObserver(NSObject, NSString) RemoveObserver(NSObject, NSString)

Stops the specified observer from receiving further notifications of changed values for the specified keyPath.

(Inherited from NSObject)
RemoveObserver(NSObject, NSString, IntPtr) RemoveObserver(NSObject, NSString, IntPtr)

Stops the specified observer from receiving further notifications of changed values for the specified keyPath and context.

(Inherited from NSObject)
RemoveObserver(NSObject, String) RemoveObserver(NSObject, String)

Stops the specified observer from receiving further notifications of changed values for the specified keyPath.

(Inherited from NSObject)
RemoveObserver(NSObject, String, IntPtr) RemoveObserver(NSObject, String, IntPtr)

Stops the specified observer from receiving further notifications of changed values for the specified keyPath and context.

(Inherited from NSObject)
RemoveObserver(NSObject, String, NSObject) RemoveObserver(NSObject, String, NSObject)
RemoveObservers(IEnumerable<NSObject>) RemoveObservers(IEnumerable<NSObject>)

Removes multiple observers in one call.

RespondsToSelector(Selector) RespondsToSelector(Selector)

Whether this object recognizes the specified selector.

(Inherited from NSObject)
SetNativeField(String, NSObject) SetNativeField(String, NSObject) Inherited from NSObject
SetNilValueForKey(NSString) SetNilValueForKey(NSString)

Sets the value of the specified key to null.

(Inherited from NSObject)
SetValueForKey(NSObject, NSString) SetValueForKey(NSObject, NSString)

Sets the value of the property specified by the key to the specified value.

(Inherited from NSObject)
SetValueForKeyPath(IntPtr, NSString) SetValueForKeyPath(IntPtr, NSString)

A constructor used when creating managed representations of unmanaged objects; Called by the runtime.

(Inherited from NSObject)
SetValueForKeyPath(NSObject, NSString) SetValueForKeyPath(NSObject, NSString)

Sets the value of a property that can be reached using a keypath.

(Inherited from NSObject)
SetValueForUndefinedKey(NSObject, NSString) SetValueForUndefinedKey(NSObject, NSString)

Indicates an attempt to write a value to an undefined key. If not overridden, raises an NSUndefinedKeyException.

(Inherited from NSObject)
SetValuesForKeysWithDictionary(NSDictionary) SetValuesForKeysWithDictionary(NSDictionary)

Sets the values of this NSObject to those in the specified dictionary.

(Inherited from NSObject)
ToString() ToString()

Returns a string representation of the value of the current instance.

(Inherited from NSObject)
ValueForKey(NSString) ValueForKey(NSString)

Returns the value of the property associated with the specified key.

(Inherited from NSObject)
ValueForKeyPath(NSString) ValueForKeyPath(NSString)

Returns the value of a property that can be reached using a keypath.

(Inherited from NSObject)
ValueForUndefinedKey(NSString) ValueForUndefinedKey(NSString)

Indicates an attempt to read a value of an undefined key. If not overridden, raises an NSUndefinedKeyException.

(Inherited from NSObject)
WillChange(NSKeyValueChange, NSIndexSet, NSString) WillChange(NSKeyValueChange, NSIndexSet, NSString)

Indicates that the values of the specified indices in the specified key are about to change.

(Inherited from NSObject)
WillChange(NSString, NSKeyValueSetMutationKind, NSSet) WillChange(NSString, NSKeyValueSetMutationKind, NSSet) Inherited from NSObject
WillChangeValue(String) WillChangeValue(String)

Indicates that the value of the specified key is about to change.

(Inherited from NSObject)

Extension Methods

GetDebugDescription(INSObjectProtocol) GetDebugDescription(INSObjectProtocol)
GetAccessibilityCustomRotors(NSObject) GetAccessibilityCustomRotors(NSObject)

Gets the array of UIAccessibilityCustomRotor objects appropriate for this object.

SetAccessibilityCustomRotors(NSObject, UIAccessibilityCustomRotor[]) SetAccessibilityCustomRotors(NSObject, UIAccessibilityCustomRotor[])

Sets the array of UIAccessibilityCustomRotor objects appropriate for this object.

Applies to

See also