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<?xml version="1.0"?>
<!DOCTYPE gsdoc PUBLIC "-//GNUstep//DTD gsdoc 1.0.4//EN" "http://www.gnustep.org/gsdoc-1_0_4.dtd">
<gsdoc base="NSKeyValueCoding" up="Base">
<head>
<title>NSKeyValueCoding informal protocol reference</title>
<author name="Richard Frith-Macdonald">
<email address="rfm@gnu.org">
rfm@gnu.org
</email>
</author>
<copy>2000,2002 Free Software Foundation, Inc.</copy>
</head>
<body>
<front><contents /></front>
<chapter>
<heading>
Software documentation for the
NSObject(NSKeyValueCoding) informal
protocol
</heading>
<category name="NSKeyValueCoding" class="NSObject" ovadd="10.0.0">
<declared>Foundation/NSKeyValueCoding.h</declared>
<desc>
<p>
This describes an informal protocol for
<em>key-value coding</em>, a mechanism whereby the
fields of an object may be accessed and set using
generic methods in conjunction with string keys
rather than field-specific methods. Key-based access
loses compile-time validity checking, but can be
convenient in certain kinds of situations.
</p>
<p>
The basic methods are implemented as a category of the
<ref type="class" id="NSObject">NSObject</ref>
class, but other classes override those default
implementations to perform more specific
operations.
</p>
</desc>
<method type="BOOL" factory="yes" ovadd="10.0.0">
<sel>accessInstanceVariablesDirectly</sel>
<desc>
Controls whether the NSKeyValueCoding methods may
attempt to access instance variables directly.
NSObject's implementation returns
<code>YES</code>.
</desc>
</method>
<method type="BOOL" factory="yes" ovadd="10.0.0">
<sel>useStoredAccessor</sel>
<desc>
Controls whether
<ref type="method" id="-storedValueForKey:">
-storedValueForKey:
</ref>
and
<ref type="method" id="-takeStoredValue:forKey:">
-takeStoredValue:forKey:
</ref>
may use the stored accessor mechanism. If not the calls
get redirected to
<ref type="method" id="-valueForKey:">
-valueForKey:
</ref>
and
<ref type="method" id="-takeValue:forKey:">
-takeValue:forKey:
</ref>
effectively changing the search order of
private/public accessor methods and instance
variables. NSObject's implementation returns
<code>YES</code>.
</desc>
</method>
<method type="NSDictionary*" ovadd="10.0.0">
<sel>dictionaryWithValuesForKeys:</sel>
<arg type="NSArray*">keys</arg>
<desc>
Returns a dictionary built from values obtained for
the specified <var>keys</var>. <br /> By default this
is derived by calling
<ref type="method" id="-valueForKey:">
-valueForKey:
</ref>
for each key. Any <code>nil</code> values obtained are
represented by an
<ref type="class" id="NSNull">NSNull</ref>
instance.
</desc>
</method>
<method type="id" ovadd="10.0.0">
<sel>handleQueryWithUnboundKey:</sel>
<arg type="NSString*">aKey</arg>
<desc>
Deprecated... use
<ref type="method" id="-valueForUndefinedKey:">
-valueForUndefinedKey:
</ref>
instead.
</desc>
</method>
<method type="void" ovadd="10.0.0">
<sel>handleTakeValue:</sel>
<arg type="id">anObject</arg>
<sel>forUnboundKey:</sel>
<arg type="NSString*">aKey</arg>
<desc>
Deprecated, use
<ref type="method" id="-setValue:forUndefinedKey:">
-setValue:forUndefinedKey:
</ref>
instead.
</desc>
</method>
<method type="NSMutableArray*" ovadd="10.0.0">
<sel>mutableArrayValueForKey:</sel>
<arg type="NSString*">aKey</arg>
<desc>
Returns a mutable array value for a given key. This
method:
<list>
<item>
Searches the receiver for methods matching the
patterns insertObject:in<Key>AtIndex:
and removeObjectFrom<Key>AtIndex:. If both
methods are found, each message sent to the
proxy array will result in the invocation of one
or more of these methods. If
replaceObjectIn<Key>AtIndex:withObject:
is also found in the receiver it will be used when
appropriate for better performance.
</item>
<item>
If the set of methods is not found, searches the
receiver for a the method set<Key>:.
Each message sent to the proxy array will result
in the invocation of set<Key>:
</item>
<item>
If the previous do not match, and
accessInstanceVariablesDirectly
returns <code>YES</code>, searches for an
instance variable matching _<key> or
<key> (in that order). If the
instance variable is found, messages sent to
the proxy object will be forwarded to the instance
variable.
</item>
<item>
If none of the previous are found, raises an
NSUndefinedKeyException
</item>
</list>
</desc>
</method>
<method type="NSMutableArray*" ovadd="10.0.0">
<sel>mutableArrayValueForKeyPath:</sel>
<arg type="NSString*">aKey</arg>
<desc>
Returns a mutable array value for the given key
path.
</desc>
</method>
<method type="NSMutableSet*" ovadd="10.0.0">
<sel>mutableSetValueForKey:</sel>
<arg type="NSString*">aKey</arg>
<desc>
Returns a mutable set value for a given key. This
method:
<list>
<item>
Searches the receiver for methods matching the
patterns add<Key>Object:,
remove<Key>Object:,
add<Key>:, and
remove<Key>:, which
correspond to the NSMutableSet methods
addObject:, removeObject:, unionSet:, and
minusSet:, respectively. If at least one
addition and one removal method are found,
each message sent to the proxy set will result in
the invocation of one or more of these methods. If
intersect<Key>: or
set<Key>: is also found in the
receiver, the method(s) will be used when
appropriate for better performance.
</item>
<item>
If the set of methods is not found, searches the
receiver for a the method set<Key>:.
Each message sent to the proxy set will result in
the invocation of set<Key>:
</item>
<item>
If the previous do not match, and
accessInstanceVariablesDirectly
returns <code>YES</code>, searches for an
instance variable matching _<key> or
<key> (in that order). If the
instance variable is found, messages sent to
the proxy object will be forwarded to the instance
variable.
</item>
<item>
If none of the previous are found, raises an
NSUndefinedKeyException
</item>
</list>
</desc>
</method>
<method type="NSMutableSet*" ovadd="10.0.0">
<sel>mutableSetValueForKeyPath:</sel>
<arg type="NSString*">aKey</arg>
<desc>
Returns a mutable set value for the given key path.
</desc>
</method>
<method type="void" ovadd="10.0.0">
<sel>setNilValueForKey:</sel>
<arg type="NSString*">aKey</arg>
<desc>
This method is invoked by the NSKeyValueCoding
mechanism when an attempt is made to set an null
value for a scalar attribute. This implementation
raises an NSInvalidArgument exception. Subclasses my
override this method to do custom handling. (E.g.
setting the value to the equivalent of 0.)
</desc>
</method>
<method type="void" ovadd="10.0.0">
<sel>setValue:</sel>
<arg type="id">anObject</arg>
<sel>forKey:</sel>
<arg type="NSString*">aKey</arg>
<desc>
Sets the value if the attribute associated with the
key in the receiver. The object is converted to a
scalar attribute where applicable (and
<ref type="method" id="-setNilValueForKey:">
-setNilValueForKey:
</ref>
is called if a <code>nil</code> value is supplied).
Tries to use a standard accessor of the form setKey:
where 'Key' is the supplied argument with the first
letter converted to uppercase. <br /> If the
receiver's class allows
<ref type="method" id="+accessInstanceVariablesDirectly">
+accessInstanceVariablesDirectly
</ref>
it continues with instance variables:
<list>
<item>_key</item> <item>_isKey</item>
<item>key</item> <item>isKey</item>
</list>
Invokes
<ref type="method" id="-setValue:forUndefinedKey:">
-setValue:forUndefinedKey:
</ref>
if no accessor mechanism can be found and raises
NSInvalidArgumentException if
the accessor method doesn't take exactly one argument
or the type is unsupported (e.g. structs). If the
receiver expects a scalar value and the value
supplied is the NSNull instance or
<code>nil</code>, this method invokes
<ref type="method" id="-setNilValueForKey:">
-setNilValueForKey:
</ref>
.
</desc>
</method>
<method type="void" ovadd="10.0.0">
<sel>setValue:</sel>
<arg type="id">anObject</arg>
<sel>forKeyPath:</sel>
<arg type="NSString*">aKey</arg>
<desc>
Retrieves the object returned by invoking
<ref type="method" id="-valueForKey:">
-valueForKey:
</ref>
on the receiver with the first key component supplied by
the key path. Then invokes
<ref type="method" id="-setValue:forKeyPath:">
-setValue:forKeyPath:
</ref>
recursively on the returned object with rest of
the key path. The key components are delimited by '.'.
If the key path doesn't contain any '.', this method
simply invokes
<ref type="method" id="-setValue:forKey:">
-setValue:forKey:
</ref>
.
</desc>
</method>
<method type="void" ovadd="10.0.0">
<sel>setValue:</sel>
<arg type="id">anObject</arg>
<sel>forUndefinedKey:</sel>
<arg type="NSString*">aKey</arg>
<desc>
Invoked when
<ref type="method" id="-setValue:forKey:">
-setValue:forKey:
</ref>
/
<ref type="method" id="-takeStoredValue:forKey:">
-takeStoredValue:forKey:
</ref>
are called with a key which can't be associated with an
accessor method or instance variable. Subclasses
may override this method to add custom handling.
NSObject raises an NSUndefinedKeyException, with a
userInfo dictionary containing
NSTargetObjectUserInfoKey with
the receiver an NSUnknownUserInfoKey with the supplied
key entries. <br /> Called when the key passed to
<ref type="method" id="-setValue:forKey:">
-setValue:forKey:
</ref>
cannot be used.
</desc>
</method>
<method type="void" ovadd="10.0.0">
<sel>setValuesForKeysWithDictionary:</sel>
<arg type="NSDictionary*">aDictionary</arg>
<desc>
Uses
<ref type="method" id="-setValue:forKey:">
-setValue:forKey:
</ref>
to place the values from <var>aDictionary</var> in the
receiver.
</desc>
</method>
<method type="id" ovadd="10.0.0">
<sel>storedValueForKey:</sel>
<arg type="NSString*">aKey</arg>
<desc>
Returns the value associated with the supplied key
as an object. Scalar attributes are converted to
corresponding objects. Uses private accessors
in favor of the public ones, if the receiver's class
allows
<ref type="method" id="+useStoredAccessor">
+useStoredAccessor
</ref>
. Otherwise this method invokes
<ref type="method" id="-valueForKey:">
-valueForKey:
</ref>
. The search order is: <br /> Private accessor methods:
<list><item>_getKey</item> <item>_key</item></list>
If the receiver's class allows
<ref type="method" id="+accessInstanceVariablesDirectly">
+accessInstanceVariablesDirectly
</ref>
it continues with instance variables:
<list><item>_key</item> <item>key</item></list>
Public accessor methods:
<list><item>getKey</item> <item>key</item></list>
Invokes
<ref type="method" id="-handleTakeValue:forUnboundKey:">
-handleTakeValue:forUnboundKey:
</ref>
if no accessor mechanism can be found and raises
NSInvalidArgumentException if
the accessor method takes takes any arguments or the
type is unsupported (e.g. structs).
</desc>
</method>
<method type="void" ovadd="10.0.0">
<sel>takeStoredValue:</sel>
<arg type="id">anObject</arg>
<sel>forKey:</sel>
<arg type="NSString*">aKey</arg>
<desc>
Sets the value associated with the supplied in the
receiver. The object is converted to the scalar
attribute where applicable. Uses the private
accessors in favor of the public ones, if the
receiver's class allows
<ref type="method" id="+useStoredAccessor">
+useStoredAccessor
</ref>
. Otherwise this method invokes
<ref type="method" id="-takeValue:forKey:">
-takeValue:forKey:
</ref>
. The search order is: <br /> Private accessor methods:
<list><item>_setKey:</item></list> If the receiver's
class allows accessInstanceVariablesDirectly it
continues with instance variables:
<list><item>_key</item> <item>key</item></list>
Public accessor methods:
<list><item>setKey:</item></list> Invokes
<ref type="method" id="-handleTakeValue:forUnboundKey:">
-handleTakeValue:forUnboundKey:
</ref>
if no accessor mechanism can be found and raises
NSInvalidArgumentException if
the accessor method doesn't take exactly one argument
or the type is unsupported (e.g. structs). If the
receiver expects a scalar value and the value
supplied is the NSNull instance or
<code>nil</code>, this method invokes
<ref type="method" id="-unableToSetNilForKey:">
-unableToSetNilForKey:
</ref>
.
</desc>
</method>
<method type="void" ovadd="10.0.0">
<sel>takeStoredValuesFromDictionary:</sel>
<arg type="NSDictionary*">aDictionary</arg>
<desc>
Iterates over the dictionary invoking
<ref type="method" id="-takeStoredValue:forKey:">
-takeStoredValue:forKey:
</ref>
on the receiver for each key-value pair, converting
NSNull to <code>nil</code>.
</desc>
</method>
<method type="void" ovadd="10.0.0">
<sel>takeValue:</sel>
<arg type="id">anObject</arg>
<sel>forKey:</sel>
<arg type="NSString*">aKey</arg>
<desc>
Sets the value if the attribute associated with the
key in the receiver. The object is converted to a
scalar attribute where applicable. Uses the public
accessors in favor of the private ones. The
search order is: <br /> Accessor methods:
<list>
<item>setKey:</item> <item>_setKey:</item>
</list>
If the receiver's class allows
<ref type="method" id="+accessInstanceVariablesDirectly">
+accessInstanceVariablesDirectly
</ref>
it continues with instance variables:
<list><item>key</item> <item>_key</item></list>
Invokes
<ref type="method" id="-handleTakeValue:forUnboundKey:">
-handleTakeValue:forUnboundKey:
</ref>
if no accessor mechanism can be found and raises
NSInvalidArgumentException if
the accessor method doesn't take exactly one argument
or the type is unsupported (e.g. structs). If the
receiver expects a scalar value and the value
supplied is the NSNull instance or
<code>nil</code>, this method invokes
<ref type="method" id="-unableToSetNilForKey:">
-unableToSetNilForKey:
</ref>
. <br /> Deprecated... use
<ref type="method" id="-setValue:forKey:">
-setValue:forKey:
</ref>
instead.
</desc>
</method>
<method type="void" ovadd="10.0.0">
<sel>takeValue:</sel>
<arg type="id">anObject</arg>
<sel>forKeyPath:</sel>
<arg type="NSString*">aKey</arg>
<desc>
Retrieves the object returned by invoking
<ref type="method" id="-valueForKey:">
-valueForKey:
</ref>
on the receiver with the first key component supplied by
the key path. Then invokes
<ref type="method" id="-takeValue:forKeyPath:">
-takeValue:forKeyPath:
</ref>
recursively on the returned object with rest of
the key path. The key components are delimited by '.'.
If the key path doesn't contain any '.', this method
simply invokes
<ref type="method" id="-takeValue:forKey:">
-takeValue:forKey:
</ref>
. <br /> Deprecated... use
<ref type="method" id="-setValue:forKeyPath:">
-setValue:forKeyPath:
</ref>
instead.
</desc>
</method>
<method type="void" ovadd="10.0.0">
<sel>takeValuesFromDictionary:</sel>
<arg type="NSDictionary*">aDictionary</arg>
<desc>
Iterates over the dictionary invoking
<ref type="method" id="-takeValue:forKey:">
-takeValue:forKey:
</ref>
on the receiver for each key-value pair, converting
NSNull to <code>nil</code>. <br /> Deprecated... use
<ref type="method" id="-setValuesForKeysWithDictionary:">
-setValuesForKeysWithDictionary:
</ref>
instead.
</desc>
</method>
<method type="void" ovadd="10.0.0">
<sel>unableToSetNilForKey:</sel>
<arg type="NSString*">aKey</arg>
<desc>
Deprecated... use
<ref type="method" id="-setNilValueForKey:">
-setNilValueForKey:
</ref>
instead.
</desc>
</method>
<method type="BOOL" ovadd="10.0.0">
<sel>validateValue:</sel>
<arg type="id*">aValue</arg>
<sel>forKey:</sel>
<arg type="NSString*">aKey</arg>
<sel>error:</sel>
<arg type="out NSError**">anError</arg>
<desc>
Returns a boolean indicating whether the object
pointed to by <var>aValue</var> is valid for
setting as an attribute of the receiver using the
name <var>aKey</var>. On success (<code>YES</code>
response) it may return a new value to be used in
<var>aValue</var>. On failure (<code>NO</code>
response) it may return an error in
<var>anError</var>. <br /> The method works by
calling a method of the receiver whose name is of
the form validateKey:error: if the receiver has
implemented such a method, otherwise it simply
returns <code>YES</code>.
</desc>
</method>
<method type="BOOL" ovadd="10.0.0">
<sel>validateValue:</sel>
<arg type="id*">aValue</arg>
<sel>forKeyPath:</sel>
<arg type="NSString*">aKey</arg>
<sel>error:</sel>
<arg type="out NSError**">anError</arg>
<desc>
Returns the result of calling
<ref type="method" id="-validateValue:forKey:error:">
-validateValue:forKey:error:
</ref>
on the receiver using aPath to determine the key value
in the same manner as the
<ref type="method" id="-valueForKeyPath:">
-valueForKeyPath:
</ref>
method.
</desc>
</method>
<method type="id" ovadd="10.0.0">
<sel>valueForKey:</sel>
<arg type="NSString*">aKey</arg>
<desc>
Returns the value associated with the supplied key
as an object. Scalar attributes are converted to
corresponding objects. <br /> The search
order is: <br /> Accessor methods:
<list><item>getKey</item> <item>key</item></list> If
the receiver's class allows
<ref type="method" id="+accessInstanceVariablesDirectly">
+accessInstanceVariablesDirectly
</ref>
it continues with private accessors:
<list><item>_getKey</item> <item>_key</item></list>
and then instance variables:
<list><item>key</item> <item>_key</item></list>
Invokes
<ref type="method" id="-setValue:forUndefinedKey:">
-setValue:forUndefinedKey:
</ref>
if no accessor mechanism can be found and raises
NSInvalidArgumentException if
the accessor method takes any arguments or the type is
unsupported (e.g. structs).
</desc>
</method>
<method type="id" ovadd="10.0.0">
<sel>valueForKeyPath:</sel>
<arg type="NSString*">aKey</arg>
<desc>
Returns the object returned by invoking
<ref type="method" id="-valueForKeyPath:">
-valueForKeyPath:
</ref>
recursively on the object returned by invoking
<ref type="method" id="-valueForKey:">
-valueForKey:
</ref>
on the receiver with the first key component supplied by
the key path. The key components are delimited by '.'.
If the key path doesn't contain any '.', this method
simply invokes
<ref type="method" id="-valueForKey:">
-valueForKey:
</ref>
.
</desc>
</method>
<method type="id" ovadd="10.0.0">
<sel>valueForUndefinedKey:</sel>
<arg type="NSString*">aKey</arg>
<desc>
Invoked when
<ref type="method" id="-valueForKey:">
-valueForKey:
</ref>
/
<ref type="method" id="-storedValueForKey:">
-storedValueForKey:
</ref>
are called with a key, which can't be associated with
an accessor method or instance variable. Subclasses may
override this method to add custom handling.
NSObject raises an NSUndefinedKeyException, with a
userInfo dictionary containing
NSTargetObjectUserInfoKey with
the receiver an NSUnknownUserInfoKey with the supplied
key entries. <br />
</desc>
</method>
<method type="NSDictionary*" ovadd="10.0.0">
<sel>valuesForKeys:</sel>
<arg type="NSArray*">keys</arg>
<desc>
Iterates over the array sending the receiver
<ref type="method" id="-valueForKey:">
-valueForKey:
</ref>
for each object in the array and inserting the result
in a dictionary. All <code>nil</code> values returned by
<ref type="method" id="-valueForKey:">
-valueForKey:
</ref>
are replaced by the NSNull instance in the dictionary.
</desc>
</method>
</category>
</chapter>
</body>
</gsdoc>
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