Write custom object to .plist in Cocoa

问题:

I am blocking into something and I am sure it is too big. I have a custom object that look like this

 @interface DownloadObject : NSObject <NSCoding>{
    NSNumber *key; 
    NSString *name; 
    NSNumber *progress; 
    NSNumber *progressBytes; 
    NSNumber *size; 
    NSString *path; 
}
@property (copy) NSNumber *key; 
@property (copy) NSString *name; 
@property (copy) NSNumber *progress; 
@property (copy) NSNumber *size; 
@property (copy) NSString *path; 
@property (copy) NSNumber *progressBytes; 
-(id)initWithKey:(NSNumber *)k name:(NSString *)n progress:(NSNumber *)pro size:(NSNumber *)s path:(NSString *)p progressBytes:(NSNumber *)pb; 
@end

And the implementation

  @implementation DownloadObject
@synthesize size, progress, name, key, path, progressBytes;

-(id)initWithKey:(NSNumber *)k name:(NSString *)n progress:(NSNumber *)pro size:(NSNumber *)s path:(NSString *)p progressBytes:(NSNumber *)pb  
{
    self.key = k;
    self.name = n; 
    self.progress = pro; 
    self.size = s; 
    self.path = p; 
    self.progressBytes = pb; 

    return self; 
}

-(id) initWithCoder: (NSCoder*) coder {
    if (self = [super init]) {
        self.key = [[coder decodeObjectForKey:@"Key"] retain];
        self.name = [[coder decodeObjectForKey:@"Name"] retain];
        self.progress = [[coder decodeObjectForKey:@"Progress"] retain];
        self.size = [[coder decodeObjectForKey:@"Size"] retain];
        self.path = [[coder decodeObjectForKey:@"Path"] retain];
        self.progressBytes = [[coder decodeObjectForKey:@"ProgressBytes"]retain]; 
    }
    return self;
}


-(void) encodeWithCoder: (NSCoder*) coder {
    [coder encodeObject:self.key forKey:@"Key"]; 
    [coder encodeObject:self.name forKey:@"Name"]; 
    [coder encodeObject:self.progress forKey:@"Progress"]; 
    [coder encodeObject:self.size forKey:@"Size"]; 
    [coder encodeObject:self.path forKey:@"Path"]; 
    [coder encodeObject:self.progressBytes forKey:@"ProgressBytes"]; 
}


-(void)dealloc
{
    [key release]; 
    [name release]; 
    [size release]; 
    [progress release]; 
    [path release]; 
    [progressBytes release]; 
    [super dealloc]; 
}

@end

As you can see it implement NSCoding (I think so, NSObject does not conform to NSCoding). Now when I try to do something like that just to test

downloadArray = [[[NSMutableArray alloc]init]retain];
NSNumber *number = [NSNumber numberWithInt:10]; 
DownloadObject *object = [[DownloadObject alloc]initWithKey:number name:@"hey" progress:number size:number path:@"hey" progressBytes:number]; 
[downloadArray addObject:object]; 
[object release]; 
[downloadArray writeToFile:path atomically:YES]; 

downloadArray is a NSMutableArray. My plist read/write is fine, the path is located in the application support and when I log it show the plist path.

But it just does not write the array to the plist, any idea ?

回答1:

Property list files can only store basic data types and cannot contain custom objects. You need to convert your object to an NSData object if you want it to be written to the plist. You can do this with NSKeyedArchiver, which will encode an object which conforms to the NSCoding protocol into an NSData object.

DownloadObject *object = [[DownloadObject alloc]initWithKey:number name:@"hey" progress:number size:number path:@"hey" progressBytes:number];
NSData* objData = [NSKeyedArchiver archivedDataWithRootObject:object];
[downloadArray addObject:objData];
[object release];

When you want to reconstruct your object from the NSData object, you use NSKeyedUnarchiver:

NSData* objData = [downloadArray objectAtIndex:0];
DownloadObject* object = [NSKeyedUnarchiver unarchiveObjectWithData:objData];

You also have several memory leaks in your code. In your -initWithCoder: method, you should not be using accessors to set the value of the ivars, you should just set the ivars directly, like so:

key = [[coder decodeObjectForKey:@"Key"] copy];

You are calling -retain and then using the accessor which is specified as copy, which will mean your object has a retain count of 2 and will not be released. In general you should avoid using accessors in init methods.

Also, in the code where you allocate your downloadArray object, you are calling -alloc and then -retain on the object, which will leave it with a retainCount of 2. You should re-read the Objective-C Memory Management Guidelines.

回答2:

This works for me:

NSMutableData *data = [[NSMutableData alloc] init];
NSKeyedArchiver *archiver = [[NSKeyedArchiver alloc] initForWritingWithMutableData:data];

[archiver encodeObject:highScoreArray forKey:kHighScoreArrayKey];

[archiver finishEncoding];

[data writeToFile:[self dataFilePath] atomically:YES];

[data release];
[archiver release];

回答3:

BOOL flag = false;

    ObjectFileClass  *obj = [yourMutableArray objectAtIndex:0];

   //TO Write Data . . .

    NSData* archiveData = [NSKeyedArchiver archivedDataWithRootObject:obj.title];
    flag =[archiveData writeToFile:path options:NSDataWritingAtomic error:&error];
}


if (flag) {
    NSLog(@"Written");

  //To Read Data . . .

    NSData *archiveData = [NSData dataWithContentsOfFile:path];
    id yourClassInstance = [NSKeyedUnarchiver unarchiveObjectWithData:archiveData]; // choose the type of your class instance  . . .
    NSLog(@"%@",yourClassInstance);
}else{

    NSLog(@"Not Written");
}