objective-c - 在 Cocoa 中将自定义对象写入 .plist

Question

我正在阻塞某些东西，我确定它太大了。我有一个看起来像这样的自定义对象

 @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

和实现

  @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

如你所见，它实现了 NSCoding(我认为是的，NSObject 不符合 NSCoding)。现在，当我尝试做类似的事情来测试时

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 是一个 NSMutableArray。我的 plist 读/写很好，path 位于应用程序支持中，当我登录它时显示 plist 路径。

但它只是不将数组写入 plist，知道吗？

Answer 1

属性列表文件只能存储基本数据类型，不能包含自定义对象。如果要将对象写入 plist，则需要将对象转换为 NSData 对象。您可以使用 NSKeyedArchiver 执行此操作，它将符合 NSCoding 协议(protocol)的对象编码为 NSData 对象。

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];

当你想从 NSData 对象重建你的对象时，你可以使用 NSKeyedUnarchiver:

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

您的代码中还有一些内存泄漏。在你的 -initWithCoder: 方法中，你不应该使用访问器来设置 ivars 的值，你应该直接设置 ivars，就像这样:

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

您正在调用 -retain，然后使用指定为 copy 的访问器，这意味着您的对象的保留计数为 2，并且不会被释放。通常，您应该避免在 init 方法中使用访问器。

此外，在您分配 downloadArray 对象的代码中，您正在调用 -alloc 然后在对象上调用 -retain，这将保留它的 retainCount 为 2。您应该重新阅读 Objective-C Memory Management Guidelines .