com.webobjects.foundation
Class NSNotification

java.lang.Object
  com.webobjects.foundation.NSNotification

All Implemented Interfaces:

NSCoding, Serializable

public class NSNotification

extends Object

implements NSCoding, Serializable

NSNotification objects encapsulate information so that it can be broadcast to other objects by an NSNotificationCenter object.

The standard way to pass information between objects is method invocation -- one object invokes the method of another object. However, method invocation requires that the object invoking the method knows which object to invoke the method on, and what messages it responds to. At times, this tight coupling of two objects is undesirable -- most notably because it would join together two otherwise independent subsystems. For these cases, a broadcast model is introduced: an object posts a notification, which is dispatched to the appropriate observers through an NSNotificationCenter object, or simply notification center.

This notification model frees an object from concern about what objects it should send information to. Any object may simply post a notification without knowing what objects -- if any -- are receiving the notification. However, objects receiving notifications will need to know at least the notification name, and possibly the type of information the notification contains. The notification center takes care of broadcasting notifications to registered observers. Another benefit of this model is to allow multiple objects to listen for notifications, which would otherwise be cumbersome.

Any object may post a notification. Other objects can register themselves as observers to receive notifications when they are posted. The object posting the notification, the object included in the notification, and the observer of the notification may all be different objects or the same object.

You can create a notification object with the constructor, however, generally, you will not need to create notifications directly. The NSNotificationCenter method postNotification allows convenient posting of a notification without creating it first.

An NSNotification object (referred to as a notification) contains a name, an object, and a userInfo. The name is a tag identifying the notification. The object is any object that the poster of the notification wants to send to observers of that notification, although typically it is the object that posted the notification. The userInfo is an NSDictionary used to store other information the sender of the notification may want to pass to observers.

NSNotification objects are immutable.

See Also:

NSNotificationCenter, NSNotificationCenter.postNotification(NSNotification notification), Serialized Form

Nested Class Summary

Nested classes inherited from class com.webobjects.foundation.NSCoding

NSCoding.Support

Constructor Summary

NSNotification(String name, Object object)
Initializes and returns a notification with name name, object object, and an empty userInfo.

NSNotification(String name, Object object, NSDictionary userInfo)
Initializes and returns a notification with name name, object object, and arbitrary user information userInfo.

Method Summary

Class	classForCoder() Returns the class that should be used for encoding the receiver in an NSCoder.
static Object	decodeObject(NSCoder coder) Creates an NSNotification from the data in coder.
void	encodeWithCoder(NSCoder coder) Encodes the receiver using coder.
boolean	equals(Object other) Compares the receiving NSNotification object to other.
int	hashCode() Provide an appropriate hash code useful for storing the receiver in a hash-based data structure.
String	name() Returns the name of the notification.
Object	object() Returns the object associated with the notification.
String	toString() Returns a string representation of the receiver including its nameobject and userInfo.
NSDictionary	userInfo() Returns the notification's userInfo dictionary.

Methods inherited from class java.lang.Object

clone, finalize, getClass, notify, notifyAll, wait, wait, wait

Constructor Detail

NSNotification

public NSNotification(String name,
                      Object object,
                      NSDictionary userInfo)

Initializes and returns a notification with name name, object object, and arbitrary user information userInfo. The userInfo parameter may be null; if so, the userInfo method will return an empty NSDictionary. name may not be null.

Parameters:

name - String name of the notification

object - Object associated with the notification

userInfo - NSDictionary of arbitrary information

NSNotification

public NSNotification(String name,
                      Object object)

Initializes and returns a notification with name name, object object, and an empty userInfo. name may not be null.

Parameters:

name - name attached to the object

object - the current notification object

Method Detail

classForCoder

public Class classForCoder()

Returns the class that should be used for encoding the receiver in an NSCoder.

Specified by:

classForCoder in interface NSCoding

Returns:

the class that should be used for encoding the receiver in an NSCoder

See Also:

NSCoder, NSCoding

decodeObject

public static Object decodeObject(NSCoder coder)

Creates an NSNotification from the data in coder.

Parameters:

coder - an NSCoder containing data that can be used to construct a new NSNotification

Returns:

an NSNotification constructed from the data in coder

See Also:

NSCoder, NSCoding

encodeWithCoder

public void encodeWithCoder(NSCoder coder)

Encodes the receiver using coder.

Specified by:

encodeWithCoder in interface NSCoding

Parameters:

coder - the NSCoder which should be used to encode the receiver

See Also:

NSCoder, NSCoding

equals

public boolean equals(Object other)

Compares the receiving NSNotification object to other. If other is an NSNotification and the contents of other are equal to the contents of the receiver, this method returns true. If not, it returns false.

Two notifications are equal if their name and userInfo are equal and their object have identical references.

Parameters:

other - the object to be compared to the current object

Returns:

true when the contents of the objects compared are same, false otherwise

See Also:

name(), object(), userInfo()

hashCode

public int hashCode()

Provide an appropriate hash code useful for storing the receiver in a hash-based data structure.

Returns:

hashcode for the receiver

name

public String name()

Returns the name of the notification. Typically, you invoke this method on the notification object passed to your notification-handler method. This notification-handler method is the method applied by the NSSelector registered with NSNotificationCenter when the observer registered to receive the notification.

Notification names can be any string. To avoid name collisions, however, you might want to use a prefix that's specific to your application.

Returns:

name of the notification

See Also:

NSSelector, NSNotificationCenter, NSUndoManager

object

public Object object()

Returns the object associated with the notification. The object returned is often the object that posted this notification. It may, however, be null, or another object entirely. Typically, you invoke this method on the notification object passed to your notification-handler method. This notification-handler method is the method applied by the NSSelector registered with NSNotificationCenter when the observer registered to receive the notification.

Returns:

the object associated with the notification

See Also:

NSSelector, NSNotificationCenter

toString

public String toString()

Returns a string representation of the receiver including its nameobject and userInfo.

Returns:

a string representation of the receiver

userInfo

public NSDictionary userInfo()

Returns the notification's userInfo dictionary. This NSDictionary stores any additional information that objects receiving the notification might use. The NSDictionary is empty if no userInfo dictionary was specified when the notification was created.

Returns:

NSDictionary associated with the notification