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NSDistantObject Class Reference

Overview

NSDistantObject is a concrete subclass of NSProxy that defines proxies for objects in other applications or threads. When a distant object receives a message, in most cases it forwards the message through its NSConnection object to the real object in another application, supplying the return value to the sender of the message if one is received, and propagating any exception back to the invoker of the method that raised it.

NSDistantObject adds two useful instance methods to those defined by NSProxy: connectionForProxy returns the NSConnection object that handles the receiver; setProtocolForProxy: establishes the set of methods the real object is known to respond to, saving the network traffic required to determine the argument and return types the first time a particular selector is forwarded to the remote proxy.

There are two kinds of distant object: local proxies and remote proxies. A local proxy is created by an NSConnection object the first time an object is sent to another application. It is used by the connection for bookkeeping purposes and should be considered private. The local proxy is transmitted over the network using the NSCoding protocol to create the remote proxy, which is the object that the other application uses. NSDistantObject defines methods for an NSConnection object to create instances, but they’re intended only for subclasses to override—you should never invoke them directly. Use the rootProxyForConnectionWithRegisteredName:host: method of NSConnection, which sets up all the required state for an object-proxy pair.

Adopted Protocols

• encodeWithCoder:

• initWithCoder:

Tasks

Creating a Local Proxy

• + proxyWithLocal:connection:
• – initWithLocal:connection:

Creating a Remote Proxy

• + proxyWithTarget:connection:
• – initWithTarget:connection:

Getting a Proxy’s NSConnection

• – connectionForProxy

Setting a Proxy’s Protocol

• – setProtocolForProxy:

Class Methods

proxyWithLocal:connection:

Returns a local proxy for a given object and connection, creating the proxy if necessary.

+ (NSDistantObject *)proxyWithLocal:(id)anObject connection:(NSConnection *)aConnection

Parameters

anObject

An object in the receiver’s address space.

aConnection

The connection for the returned proxy.

Return Value

A local proxy for anObject and aConnection, creating it if necessary.

Discussion

Other applications connect to the proxy using the NSConnection connectionWithRegisteredName:host: class method.

Local proxies should be considered private to their NSConnection objects. Only an NSConnection object should use this method to create them, and your code shouldn’t retain or otherwise use local proxies.

Availability

• Available in Mac OS X v10.0 and later.

See Also

• – initWithLocal:connection:

Declared In

NSDistantObject.h

proxyWithTarget:connection:

Returns a remote proxy for a given object and connection, creating the proxy if necessary.

+ (NSDistantObject *)proxyWithTarget:(id)remoteObject connection:(NSConnection *)aConnection

Parameters

remoteObject

An object in another thread or another application’s address space.

aConnection

The connection to set as the NSConnection object for the returned proxy—it should have been created using the NSConnection connectionWithRegisteredName:host: class method.

Return Value

A remote proxy for remoteObject and aConnection, creating the proxy if necessary

Discussion

A remote proxy cannot be used until its connection's peer has a local proxy representing remoteObject in the other application.

Availability

• Available in Mac OS X v10.0 and later.

See Also

• – initWithTarget:connection:

Declared In

NSDistantObject.h

Instance Methods

connectionForProxy

Returns the connection used by the receiver.

- (NSConnection *)connectionForProxy

Return Value

The connection used by the receiver.

Availability

• Available in Mac OS X v10.0 and later.

Declared In

NSDistantObject.h

initWithLocal:connection:

Initializes an NSDistantObject object as a local proxy for a given object.

- (id)initWithLocal:(id)anObject connection:(NSConnection *)aConnection

Parameters

anObject

An object in the receiver’s address space.

aConnection

The connection for the returned proxy.

Return Value

An initialized NSDistantObject object that serves as a local proxy for anObject. If a proxy for anObject and aConnection already exists, the receiver is released and the existing proxy is retained and returned.

Discussion

Other applications connect to the proxy using the NSConnectionconnectionWithRegisteredName:host: class method.

Local proxies should be considered private to their NSConnection objects. Only an NSConnection object should use this method to create them, and your code shouldn’t retain or otherwise use local proxies.

This is the designated initializer for local proxies. It returns an initialized object, which might be different than the original receiver

Availability

• Available in Mac OS X v10.0 and later.

See Also

• + proxyWithLocal:connection:

Declared In

NSDistantObject.h

initWithTarget:connection:

Initializes a newly allocated NSDistantObject as a remote proxy for remoteObject, which is an id in another thread or another application’s address space.

- (id)initWithTarget:(id)remoteObject connection:(NSConnection *)aConnection

Parameters

remoteObject

An object in another thread or another application’s address space.

aConnection

The connection to set as the NSConnection object for the returned proxy—it should have been created using the NSConnectionconnectionWithRegisteredName:host: class method.

Return Value

An NSDistantObject object initialized as a remote proxy for remoteObject. If a proxy for remoteObject and aConnection already exists, the receiver is released and the existing proxy is retained and returned.

Discussion

A remote proxy can’t be used until its connection’s peer has a local proxy representing remoteObject in the other application.

This is the designated initializer for remote proxies. It returns an initialized object, which might be different than the original receiver.

Availability

• Available in Mac OS X v10.0 and later.

See Also

• + proxyWithTarget:connection:

Declared In

NSDistantObject.h

setProtocolForProxy:

Sets the methods known to be handled by the receiver to those in a given protocol.

- (void)setProtocolForProxy:(Protocol *)aProtocol

Parameters

aProtocol

The protocol for the receiver.

Discussion

Setting a protocol for a remote proxy reduces network traffic needed to determine method argument and return types.

In order to encode a message’s arguments for transmission over the network, the types of those arguments must be known in advance. When they’re not known, the distributed objects system must send an initial message just to get those types, doubling the network traffic for every new message sent. Setting a protocol alleviates this need for methods defined by the protocol. You can still send messages that aren’t declared in aProtocol—in this case the initial message is sent to determine the types, and then the real message is sent.

Availability

• Available in Mac OS X v10.0 and later.

Related Sample Code

• SimpleThreads

Declared In

NSDistantObject.h

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