libs-base/Headers/Foundation/NSKeyValueCoding.h

/* Interface for NSKeyValueCoding for GNUStep
   Copyright (C) 2000 Free Software Foundation, Inc.

   Written by:  Richard Frith-Macdonald <rfm@gnu.org>
   Date:	2000
   
   This file is part of the GNUstep Base Library.

   This library is free software; you can redistribute it and/or
   modify it under the terms of the GNU Library General Public
   License as published by the Free Software Foundation; either
   version 2 of the License, or (at your option) any later version.
   
   This library is distributed in the hope that it will be useful,
   but WITHOUT ANY WARRANTY; without even the implied warranty of
   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
   Library General Public License for more details.
   
   You should have received a copy of the GNU Library General Public
   License along with this library; if not, write to the Free
   Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston,
   MA 02111 USA.
   */ 

#ifndef __NSKeyValueCoding_h_GNUSTEP_BASE_INCLUDE
#define __NSKeyValueCoding_h_GNUSTEP_BASE_INCLUDE

#include	<Foundation/NSObject.h>

@class NSArray;
@class NSMutableArray;
@class NSDictionary;
@class NSError;
@class NSString;

#ifndef	STRICT_OPENSTEP

/** An exception for an unknown key in [NSObject(NSKeyValueCoding)]. */
GS_EXPORT NSString* const NSUndefinedKeyException;

/**
 * <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 [NSObject] class,
 * but other classes override those default implementations to perform more
 * specific operations.</p>
 */
@interface NSObject (NSKeyValueCoding)

/**
 * Controls whether the NSKeyValueCoding methods may attempt to
 * access instance variables directly.
 * NSObject's implementation returns YES.
 */
+ (BOOL) accessInstanceVariablesDirectly;

/**
 * Controls whether -storedValueForKey: and -takeStoredValue:forKey: may use
 * the stored accessor mechanism.  If not the calls get redirected to
 * -valueForKey: and -takeValue:forKey: effectively changing the search order
 * of private/public accessor methods and instance variables.
 * NSObject's implementation returns YES.
 */
+ (BOOL) useStoredAccessor;

/**
 * Returns a dictionary built from values obtained for the specified keys.<br />
 * By default this is derived by calling -valueForKey: for each key.
 * Any nil values obtained are represented by an [NSNull] instance.
 */
- (NSDictionary*) dictionaryWithValuesForKeys: (NSArray*)keys;

/**
 * Deprecated ... use -valueForUndefinedKey: instead.
 */
- (id) handleQueryWithUnboundKey: (NSString*)aKey;

/**
 * Deprecated, use -setValue:forUndefinedKey: instead.
 */
- (void) handleTakeValue: (id)anObject forUnboundKey: (NSString*)aKey;

/**
 * <strong>Not implemented</strong> ... I don't know what this method
 * is good for ... do we need to copy MacOS-X and implement it?
 */
- (NSMutableArray*) mutableArrayValueForKey: (NSString*)aKey;

/**
 * <strong>Not implemented</strong> ... I don't know what this method
 * is good for ... do we need to copy MacOS-X and implement it?
 */
- (NSMutableArray*) mutableArrayValueForKeyPath: (NSString*)aKey;

/**
 * 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.)
 */
- (void) setNilValueForKey: (NSString*)aKey;

/**
 * Sets the value if the attribute associated with the key in the receiver.
 * The object is converted to a scalar attribute where applicable (and
 * -setNilValueForKey: is called if a nil 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 +accessInstanceVariablesDirectly
 * it continues with instance variables:
 * <list>
 *  <item>_key</item>
 *  <item>_isKey</item>
 *  <item>key</item>
 *  <item>isKey</item>
 * </list>
 * Invokes -setValue:forUndefinedKey: 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 nil, this method invokes 
 * -setNilValueForKey: .
 */
- (void) setValue: (id)anObject forKey: (NSString*)aKey;

/**
 * Retrieves the object returned by invoking -valueForKey:
 * on the receiver with the first key component supplied by the key path.
 * Then invokes -setValue:forKeyPath: 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 -setValue:forKey:.
 */
- (void) setValue: (id)anObject forKeyPath: (NSString*)aKey;

/**
 * Invoked when -setValue:forKey: / -takeStoredValue:forKey: 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 -setValue:forKey: cannot be used.
 */
- (void) setValue: (id)anObject forUndefinedKey: (NSString*)aKey;

/**
 * Uses -setValue:forKey: to place the values from aDictionary in the
 * receiver.
 */
- (void) setValuesForKeysWithDictionary: (NSDictionary*)aDictionary;

/**
 * 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 +useStoredAccessor.  Otherwise this method invokes
 * -valueForKey:.
 * The search order is:<br/>
 * Private accessor methods:
 * <list>
 *  <item>_getKey</item>
 *  <item>_key</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>getKey</item>
 *  <item>key</item>
 * </list>
 * Invokes -handleTakeValue:forUnboundKey: 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).
 */
- (id) storedValueForKey: (NSString*)aKey;

/**
 * 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 +useStoredAccessor .
 * Otherwise this method invokes -takeValue:forKey: .
 * 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 -handleTakeValue:forUnboundKey:
 * 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 nil, this method invokes 
 * -unableToSetNilForKey: .
 */
- (void) takeStoredValue: (id)anObject forKey: (NSString*)aKey;

/**
 * Iterates over the dictionary invoking -takeStoredValue:forKey:
 * on the receiver for each key-value pair, converting NSNull to nil.
 */
- (void) takeStoredValuesFromDictionary: (NSDictionary*)aDictionary;

/**
 * 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 +accessInstanceVariablesDirectly
 * it continues with instance variables:
 * <list>
 *  <item>key</item>
 *  <item>_key</item>
 * </list>
 * Invokes -handleTakeValue:forUnboundKey:
 * 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 nil, this method invokes 
 * -unableToSetNilForKey: .<br />
 * Deprecated ... use -setValue:forKey: instead.
 */
- (void) takeValue: (id)anObject forKey: (NSString*)aKey;

/**
 * Retrieves the object returned by invoking -valueForKey:
 * on the receiver with the first key component supplied by the key path.
 * Then invokes -takeValue:forKeyPath: 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 -takeValue:forKey:.<br />
 * Deprecated ... use -setValue:forKeyPath: instead.
 */
- (void) takeValue: (id)anObject forKeyPath: (NSString*)aKey;

/**
 * Iterates over the dictionary invoking -takeValue:forKey:
 * on the receiver for each key-value pair, converting NSNull to nil.<br />
 * Deprecated ... use -setValuesForKeysWithDictionary: instead.
 */
- (void) takeValuesFromDictionary: (NSDictionary*)aDictionary;

/**
 * Deprecated ... use -setNilValueForKey: instead.
 */
- (void) unableToSetNilForKey: (NSString*)aKey;


/**
 * Returns a boolean indicating whether the object pointed to by aValue
 * is valid for setting as an attribute of the receiver using the name
 * aKey.  On success (YES response) it may return a new value to be used
 * in aValue.  On failure (NO response) it may return an error in anError.<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 YES.
 */
- (BOOL) validateValue: (id*)aValue
		forKey: (NSString*)aKey
		 error: (NSError**)anError;

/**
 * Returns the result of calling -validateValue:forKey:error: on the receiver
 * using aPath to determine the key value in the same manner as the
 * -valueForKeyPath: method.
 */
- (BOOL) validateValue: (id*)aValue
	    forKeyPath: (NSString*)aKey
		 error: (NSError**)anError;

/**
 * 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 +accessInstanceVariablesDirectly
 * 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 -setValue:forUndefinedKey:
 * 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).
 */
- (id) valueForKey: (NSString*)aKey;

/**
 * Returns the object returned by invoking -valueForKeyPath:
 * recursively on the object returned by invoking -valueForKey:
 * 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 -valueForKey: .
 */
- (id) valueForKeyPath: (NSString*)aKey;

/**
 * Invoked when -valueForKey: / -storedValueForKey: 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 />
 */
- (id) valueForUndefinedKey: (NSString*)aKey;

/**
 * Iterates over the array sending the receiver -valueForKey:
 * for each object in the array and inserting the result in a dictionary.
 * All nil values returned by -valueForKey: are replaced by the
 * NSNull instance in the dictionary.
 */
- (NSDictionary*) valuesForKeys: (NSArray*)keys;

@end

#endif
#endif