Question

在我的应用程序中，我正在尝试保存地图上的图钉，以便在用户终止后打开应用程序时它们就在那里。我已经将我的mkAnnotation类符合NSCoding，并实现了两个必需的方法。注释都存储在单例类中的NSMutableArray中，所以我真的只是想在单例类中保存数组。一切都编码正常，但我不认为它们正在被解码。这是一些代码：这是我的MKAnnotation类：

#import <CoreLocation/CoreLocation.h>
#import <MapKit/MapKit.h>

@interface MapPoint : NSObject <MKAnnotation, NSCoding>
{
}

- (id)initWithAddress:(NSString*)address
        coordinate:(CLLocationCoordinate2D)coordinate
                title:(NSString *)t;

@property (nonatomic, readwrite) CLLocationCoordinate2D coordinate;

//This is an optional property from MKAnnotataion
@property (nonatomic, copy) NSString *title;
@property (nonatomic, readonly, copy) NSString *subtitle;
@property (nonatomic) BOOL animatesDrop;
@property (nonatomic) BOOL canShowCallout;

@property (copy) NSString *address;
@property (nonatomic, copy) NSString *imageKey;
@property (nonatomic, copy) UIImage *image;

@end 

@implementation MapPoint

@synthesize title, subtitle, animatesDrop, canShowCallout, imageKey, image;
@synthesize address = _address, coordinate = _coordinate;

-(id)initWithAddress:(NSString *)address
       coordinate:(CLLocationCoordinate2D)coordinate
            title:(NSString *)t {
    self = [super init];

    if (self) {
        _address = [address copy];
        _coordinate = coordinate;

        [self setTitle:t];

        NSDate *theDate = [NSDate date];

        subtitle = [NSDateFormatter localizedStringFromDate:theDate
                                                  dateStyle:NSDateFormatterShortStyle
                                                  timeStyle:NSDateFormatterShortStyle];
    }
    return self;
}

- (void)encodeWithCoder:(NSCoder *)aCoder {

    [aCoder encodeObject:_address forKey:@"address"];

    NSLog(@"ENCODING coordLatitude %f coordLongitude %f ", _coordinate.latitude, _coordinate.longitude);
    [aCoder encodeDouble:_coordinate.longitude forKey:@"coordinate.longitude"];
    [aCoder encodeDouble:_coordinate.latitude forKey:@"coordinate.latitude"];

    [aCoder encodeObject:title forKey:@"title"];
}

- (id)initWithCoder:(NSCoder *)aDecoder {
    self = [super init];
    if (self) {
        [self setAddress:[aDecoder decodeObjectForKey:@"address"]];

        NSLog(@"DECODING coordLatitude %f coordLongitude %f ", _coordinate.latitude, _coordinate.longitude);
        _coordinate.longitude = [aDecoder decodeDoubleForKey:@"coordinate.longitude"];
        _coordinate.latitude = [aDecoder decodeDoubleForKey:@"coordinate.latitude"];

        [self setTitle:[aDecoder decodeObjectForKey:@"title"]];
    }
    return self;
}

@end

这是我的单身人士课程：

#import <Foundation/Foundation.h>
@class MapPoint;

@interface Data : NSObject
{
NSMutableArray *_annotations;
}

@property (retain, nonatomic) NSMutableArray *annotations;

+ (Data *)singleton;
- (NSString *)pinArchivePath;
- (BOOL)saveChanges;

@end

@implementation Data

@synthesize annotations = _annotations;

+ (Data *)singleton {
    static dispatch_once_t pred;
    static Data *shared = nil;
    dispatch_once(&pred, ^{
        shared = [[Data alloc] init];
        shared.annotations = [[NSMutableArray alloc]init];
    });
    return shared;
}

- (id)init {
    self = [super init];
    if (self) {
        NSString *path = [self pinArchivePath];
        _annotations = [NSKeyedUnarchiver unarchiveObjectWithFile:path];
        if (!_annotations) {
            _annotations = [[NSMutableArray alloc]init];
        }
    }
    return self;
}

- (NSString *)pinArchivePath {
    NSArray *cachesDirectories = NSSearchPathForDirectoriesInDomains(NSCachesDirectory, NSUserDomainMask, YES);

    NSString *cachesDirectory = [cachesDirectories objectAtIndex:0];

    return [cachesDirectory stringByAppendingPathComponent:@"pins.archive"];
}

- (BOOL)saveChanges {
    NSString *path = [self pinArchivePath];

    return [NSKeyedArchiver archiveRootObject:[Data singleton].annotations
                                       toFile:path];
}

@end

在地图视图控制器上的viewDidLoad方法中，我尝试将注释放在地图上的单例数组中：

for (MapPoint *mp in [Data singleton].annotations) {
        [_worldView addAnnotation:mp];
}

Answer 1

主要问题在于这些行中的singleton方法：

dispatch_once(&pred, ^{
    shared = [[Data alloc] init];
    shared.annotations = [[NSMutableArray alloc]init]; //<-- problem line
});

shared = [[Data alloc] init];行解码并初始化annotations数组。

然后shared.annotations = [[NSMutableArray alloc]init];行重新创建并重新初始化annotations数组，从而丢弃刚刚解码的注释，以便单例始终返回一个空数组。

删除shared.annotations = [[NSMutableArray alloc]init];行。

正如评论中已经提到的那样，导致简单混淆的另一个小问题是放置正在解码坐标的NSLog。解码完成后，NSLog应为。

地图坐标不解码

1 个答案: