# NSInvocation class reference

richard@brainstorm.co.uk
mccallum@gnu.ai.mit.edu
Generated at 2025-12-02 21:52:00 +0000
1998,2003 Free Software Foundation, Inc.
Software documentation for the NSInvocation class
Foundation/NSInvocation.h

The `NSInvocation` class implements a mechanism of constructing messages (as `NSInvocation` instances), sending these to other objects, and handling the returned values.

An `NSInvocation` object may contain a target object to which a message can be sent, or may send the message to an arbitrary object.
Each message consists of a selector for that method and an argument list. Once the message has been sent, the invocation will contain a return value whose contents may be copied out of it.

The target, selector, and arguments of an instance be constructed dynamically, providing a great deal of power/flexibility.

The sending of the message to the target object (using the -invoke or -invokeWithTarget: method) can be done at any time, but a standard use of this is by the [NSObject -forwardInvocation:] method which is called whenever a method is not implemented by the class of the object to which it was sent.

Related to the class are two convenience macros... NS_MESSAGE() and NS_INVOCATION() ... to allow easy construction of invocations with all the arguments set up.

Warning the underscore at the start of the name of this instance variable indicates that, even though it is not technically private, it is intended for internal use within the package, and you should not use the variable in other code.
Warning the underscore at the start of the name of this instance variable indicates that, even though it is not technically private, it is intended for internal use within the package, and you should not use the variable in other code.
Warning the underscore at the start of the name of this instance variable indicates that, even though it is not technically private, it is intended for internal use within the package, and you should not use the variable in other code.
Warning the underscore at the start of the name of this instance variable indicates that, even though it is not technically private, it is intended for internal use within the package, and you should not use the variable in other code.
Warning the underscore at the start of the name of this instance variable indicates that, even though it is not technically private, it is intended for internal use within the package, and you should not use the variable in other code.
Warning the underscore at the start of the name of this instance variable indicates that, even though it is not technically private, it is intended for internal use within the package, and you should not use the variable in other code.
Warning the underscore at the start of the name of this instance variable indicates that, even though it is not technically private, it is intended for internal use within the package, and you should not use the variable in other code.
Warning the underscore at the start of the name of this instance variable indicates that, even though it is not technically private, it is intended for internal use within the package, and you should not use the variable in other code.
Warning the underscore at the start of the name of this instance variable indicates that, even though it is not technically private, it is intended for internal use within the package, and you should not use the variable in other code.
Warning the underscore at the start of the name of this instance variable indicates that, even though it is not technically private, it is intended for internal use within the package, and you should not use the variable in other code.
Warning the underscore at the start of the name of this instance variable indicates that, even though it is not technically private, it is intended for internal use within the package, and you should not use the variable in other code.
Warning the underscore at the start of the name of this instance variable indicates that, even though it is not technically private, it is intended for internal use within the package, and you should not use the variable in other code.
invocationWithMethodSignature:
_signature
Returns an invocation instance which can be used to send messages to a target object using the described signature.
You must set the target and selector (using -setTarget: and -setSelector:) before you attempt to use the invocation.
Raises an NSInvalidArgumentException if the signature is `nil`.
argumentsRetained
Returns a flag to indicate whether object arguments of the invocation (including its target) are retained by the invocation.
getArgument:
buffer
atIndex:
index
Copies the argument identified by index into the memory location specified by the buffer argument.
An index of zero is the target object, an index of one is the selector, so the actual method arguments start at index 2.
getReturnValue:
buffer
Copies the invocations return value to the location pointed to by buffer if a return value has been set (see the -setReturnValue: method).
If there isn't a return value then this method raises an exception.
invoke
Sends the message encapsulated in the invocation to its target.
invokeWithTarget:
anObject
Sends the message encapsulated in the invocation to anObject.
methodSignature
Returns the method signature of the invocation.
retainArguments
Instructs the invocation to retain its object arguments (including the target). The default is not to retain them.
retainArgumentsIncludingTarget:
retainTargetFlag
Similar to -[NSInvocation retainArguments], but allows the sender to explicitly control whether the target is retained as well. Retaining the target is sometimes not desirable (such as in NSUndoManager), as retain loops could result.
selector
Returns the selector of the invocation (the argument at index 1)
setArgument:
buffer
atIndex:
index
Sets the argument identified by index from the memory location specified by the buffer argument.
Using an index of 0 is equivalent to calling -setTarget: and using an argument of 1 is equivalent to -setSelector:
Proper arguments start at index 2.
NB. Unlike -setTarget: and -setSelector: the value of buffer must be a pointer to the argument to be set in the invocation.
If -retainArguments was called, then any object argument set in the receiver is retained by it.
setReturnValue:
buffer
Sets the return value of the invocation to the item that buffer points to.
setSelector:
aSelector
Sets the selector for the invocation.
setTarget:
anObject
Sets the target object for the invocation.
If -retainArguments was called, then the target is retained.
target
Returns the target object of the invocation.
targetRetained
Returns `YES` if target has been retained yet, `NO` otherwise.
Software documentation for the NSInvocation(GNUstep) category
Foundation/NSInvocation.h
Provides some minor extensions and some utility methods to aid integration of `NSInvocation` with the Objective-C runtime.
sendsToSuper
Returns the status of the flag set by -setSendsToSuper:
setSendsToSuper:
flag
Sets the flag to tell the invocation that it should actually invoke a method in the superclass of the target rather than the method of the target itself.
This extension permits an invocation to act like a regular method call sent to super in the method of a class.
Software documentation for the NSInvocation(MacroSetup) category
Foundation/NSInvocation.h
For use by macros only.
These methods are for internal use only... not public API
They are used by the NS_INVOCATION() and NS_MESSAGE() macros to help create invocations.
_newProxyForInvocation:
target
Warning the underscore at the start of the name of this method indicates that it is private, for internal use only, and you should not use the method in your code.
Internal use.
_newProxyForMessage:
target
Warning the underscore at the start of the name of this method indicates that it is private, for internal use only, and you should not use the method in your code.
_returnInvocationAndDestroyProxy:
proxy
Warning the underscore at the start of the name of this method indicates that it is private, for internal use only, and you should not use the method in your code.
initWithMethodSignature:
aSignature
Initialised an invocation instance which can be used to send messages to a target object using aSignature.
You must set the target and selector (using -setTarget: and -setSelector:) before you attempt to use the invocation.
Raises an NSInvalidArgumentException if aSignature is `nil`.