NSKeyedArchiver/NSKeyedUnarchiver
NSKeyedArchiver/NSKeyedUnarchiver
- Subject: NSKeyedArchiver/NSKeyedUnarchiver
- From: Michael Monscheuer <email@hidden>
- Date: Sat, 30 Aug 2003 16:16:01 +0200
Hi!
Saving a keyed archive and analysing the resulting file, I ran into a
problem of understanding:
After reading the documentation carefully, I expected a keyed saving of
instance variables as I can access them via keys within initWithCoder:
while decoding file. It is not:
The resulting file contains all data - but unkeyed and in the order the
instance variables where encoded in encodeWithCoder:.
Although the keys are not stored to the XML file, the access by keys in
initWithCoder: does work magically correct.
These facts (you may want to check this out using the little test
programm I attached) made me want to ask the following questions:
1) How does NSUnarchiver find out which value matches which key, so that
decodeObjectForKey: gives the correct result?
2) The written archive is readable XML, though documentation says "The
format of the archive is NSPropertyListBinaryFormat_v1_0." for
archiveRootObject:toFile:. The result seems not very Binary. Is this a
bug? I did not managed (even using NSKeyedArchiver's setOutputFormat:
method) to write another format as the XML you find attached.
3) As there are no keys for instance variables written to the file,
other applications (maybe on other platforms) must rely on the
application writing the varibles in a specific order and so these other
applications do not profit from keyed accessability (e.g. using XPath).
Is this correct?
4) Is there a way to write the instance variable keys to the file
without subclassing, which I am too blind to see?
Thanks for reading,
MiMo
//
// main.m
// KeyedArchiverTest
//
// Created by Michael Monscheuer on Sat Aug 30 2003.
// Copyright (c) 2003 __MyCompanyName__. All rights reserved.
//
#import <Cocoa/Cocoa.h>
#import <Foundation/Foundation.h>
/*******************************/
/* class interface */
/*******************************/
@interface MyObject : NSObject <NSCoding>
{
NSString *firstString;
NSString *secondString;
}
-(id)init;
-(void)setString:(NSString *)string1 andString:(NSString *)string2;
-(void)logStrings;
@end
/*******************************/
/* class implementation */
/*******************************/
@implementation MyObject
/* ------ init ------- */
-(id)init
{
self = [super init];
firstString = secondString = nil;
return self;
} // -init
/* ------ setString:andString ------- */
-(void)setString:(NSString *)string1 andString:(NSString *)string2
{
[string1 retain];
firstString = string1;
[string2 retain];
secondString = string2;
} // -setString:andString:
/* ------ logStrings ------- */
-(void)logStrings
{
NSLog(@"1:%@,2:%@\n",firstString,secondString);
} // -logStrings
/* ------ encodeWithCoder: ------- */
- (void)encodeWithCoder:(NSCoder*)coder
{
if ([coder allowsKeyedCoding])
{
[coder encodeObject:firstString forKey:@"WhereAmI_1"];
[coder encodeObject:secondString forKey:@"WhereAmI_2"];
}
else NSLog(@"not supported yet..");
} // -encodeWithCoder:
/* ------ initWithCoder: ------- */
- (id)initWithCoder:(NSCoder *)coder
{
if (self = [super init])
{
if ([coder allowsKeyedCoding])
{
secondString = [[coder decodeObjectForKey:@"WhereAmI_2"]
retain];
firstString = [[coder decodeObjectForKey:@"WhereAmI_1"]
retain];
}
else NSLog(@"not supported yet..");
}
return self;
} // initWithCoder:
@end
/*******************************/
/* main */
/*******************************/
int main(int argc, const char *argv[])
{
id obid; // object id
// create autorelease pool
NSAutoreleasePool *pool = [[NSAutoreleasePool alloc]init];
// create instance of MyObject
obid = [[[MyObject alloc]init]autorelease];
// set two strings to instance
[obid setString:@"HelloWorld!" andString:@"WhereAreTheKeys?"];
// log strings
NSLog(@"before:");
[obid logStrings];
// call keyed archiver
if (![NSKeyedArchiver archiveRootObject:obid toFile:@"keyedTest.xml"])
{
NSLog(@"Could not create keyed archive.");
return 1;
}
// unarchive stored file
obid = [NSKeyedUnarchiver unarchiveObjectWithFile:@"keyedTest.xml"];
// log strings of unarchived object
NSLog(@"after:");
[obid logStrings];
// release pool
[pool release];
return 0; // exit
} // main()
/* -------------------*/
/* The resulting file */
/* ------------------ */
/*
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE plist PUBLIC "-//Apple Computer//DTD PLIST 1.0//EN"
"
http://www.apple.com/DTDs/PropertyList-1.0.dtd";>
<plist version="1.0">
<dict>
<key>$archiver</key>
<string>NSKeyedArchiver</string>
<key>$objects</key>
<array>
<string>$null</string>
<dict/>
<string>HelloWorld!</string>
<string>WhereAreTheKeys?</string>
<dict>
<key>$classes</key>
<array>
<string>MyObject</string>
<string>NSObject</string>
</array>
<key>$classname</key>
<string>MyObject</string>
</dict>
</array>
<key>$top</key>
<dict/>
<key>$version</key>
<integer>100000</integer>
</dict>
</plist>
*/
--
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