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Copyright (c) 1994 by NeXT Computer, Inc. All Rights
Inherits From: NSObject
Conforms To: NSCoding
Declared In: Foundation/NSInvocation.h
Objects of the NSInvocation class provide a system-independent means to
construct message calls to other objects. An NSInvocation object constructs a
target object to which a message can be sent, a selector for that
method, an argument list for the selector, and a return value.
NSInvocation objects provide great flexibility in that the methods, method
arguments, and targets of the methods may be constructed dynamically.
The final sending of the message to the target object can be performed at any
time, independent of constructing the invocation. For example, methods could be
dispatched based on timer events. In addition, return values from the methods
are stored in the NSInvocation object and can be retrieved at any later stage
Also see NSMethodSignature for a description of how to construct method
The Foundation/NSInvocation.h header file defines two macros that may be
used as constructors for invocations:
NSInvocation *invocation = NS_MESSAGE(target,
builds an invocation containing a message to a known target
object. target is an object id. message consists of a selector
followed by any arguments, just like an Objective-C message.
NSInvocation *invocation = NS_INVOCATION(class, message)
builds an invocation containing a message to the untargeted class
object class. message consists of a selector followed by
any arguments, just like an Objective-C message.
Managing Invocation Arguments
- + (NSInvocation *)invocationWithMethodSignature:(NSMethodSignature
Returns an invocation object able to construct calls to objects using
method selectors with type signatures described by sig. Raises
NSInvalidArgumentException if sig is nil.
Dispatching an Invocation
- - (BOOL)argumentsRetained Returns YES if arguments are retained.
- - (void)getArgument:(void *)argumentLocation Copies the argument
stored at index into the storage
atIndex:(int)index pointed to by argumentLocation where 2
is the index of the first argument, 3 is the index of the second, and so on.
- - (void)getReturnValue:(void *)retLoc Copies the invocation's
return value into the storage pointed to by retLoc.
- - (NSMethodSignature *)methodSignature Returns the invocation's method
- - (void)retainArguments By default, target and arguments are not
retained, and C strings are not copied. This method instructs the invocation to
retain its arguments, target, and make copies of C strings. This method is
invoked automatically by timers. This method should be invoked whenever the
dynamic scope of the invocation can exceed its arguments.
- - (SEL)selector Returns the invocation's selector.
- - (void)setArgument:(void *)argumentLocation Sets the argument
stored at index to the storage pointed to
atIndex:(int)index by argumentLocation where 2 is the
index of the first argument, 3 is the index of the second, and so on..
- - (void)setReturnValue:(void *)retLoc Sets the invocation's
return value to that indicated by retLoc.
- - (void)setSelector:(SEL)selector Sets the invocation's selector
- - (void)setTarget:(id)target Sets the invocation's target to
- - (id)target Returns the invocation's target; returns nil if
there is no target.
- - (void)invoke Causes the message encoded in the invocation to be
dispatched to its target.
- - (void)invokeWithTarget:(id)target Causes the message encoded in
the invocation to be dispatched to target.