ios - 如何将 MKOverlay 对象存储到文件以便稍后检索

Question

我正在编写一个 iOS 应用程序来记录您的旅行路径，然后将其存储起来以便以后检索。大部分绘制路径的代码都是基于示例代码Breadcrumb 。

现在我正在添加功能来保存绘制的叠加层。最好的方法是什么？我可以使用 CoreData，但我不想对绘制的叠加层做太多事情，而不是稍后再次检索它。我目前尝试了一个简单的 NSArray。我将 CrumbPath 对象转换为 NSData 并将其存储在数组中。后来我检索它并将其转换回 CrumbPath。不过，我好像做错了什么。

@interface CrumbPath : NSObject <MKOverlay>
{
    MKMapPoint *points;
    NSUInteger pointCount;
    NSUInteger pointSpace;

    MKMapRect boundingMapRect;

    pthread_rwlock_t rwLock;
}

- (id)initWithCenterCoordinate:(CLLocationCoordinate2D)coord;
- (MKMapRect)addCoordinate:(CLLocationCoordinate2D)coord;

@property (readonly) MKMapPoint *points;
@property (readonly) NSUInteger pointCount;

@end

我像这样保存 CrumbPath 对象“crumbs”:

NSData *pointData = [NSData dataWithBytes:crumbs.points length:crumbs.pointCount * sizeof(MKMapPoint)];
[patternArray addObject:pointData];
[timeArray addObject:date];

NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);
NSString *documentsDirectory = [paths objectAtIndex:0];
// Create the full file path by appending the desired file name
NSString *patternFile = [documentsDirectory stringByAppendingPathComponent:@"patterns.dat"];
NSString *timeFile = [documentsDirectory stringByAppendingPathComponent:@"times.dat"];

//Save the array
[patternArray writeToFile:patternFile atomically:YES];
[timeArray writeToFile:timeFile atomically:YES];

然后像这样检索它以显示在表格中:

NSData *pointData = [appDelegate.patternArray objectAtIndex:indexPath.row];
MKMapPoint *points = malloc(pointData.length);
(void)memcpy([pointData bytes], points, sizeof(pointData));

并再次构造路径:

crumbs = [[CrumbPath alloc] initWithCenterCoordinate:MKCoordinateForMapPoint(points[0])];
for (int i = 1; i <= pointCount; i++) {
    [crumbs addCoordinate:MKCoordinateForMapPoint(points[i])];
}    
[map addOverlay:crumbs];

但是，我收到错误:'NSInvalidArgumentException'，原因:'-[NSConcreteData isEqualToString:]:无法识别的选择器发送到实例

Answer 1

就我个人而言，我倾向于这样做:

1. 首先，我倾向于保存传递给 MKPolygon 实例方法 polygonWithCoordinates 的 CLLocationCooperative2D 坐标的 C 数组(而不是 MKMapPoint C 数组)。如果您更愿意使用 MKMapPoints，则可以调整此代码，但我更喜欢一种可以在外部检查并理解的格式(即 CLLocationCooperative2D 的纬度和经度值) )。因此，我们假设您使用如下代码来制作 MKPolygon:

   MKPolygon* poly = [MKPolygon polygonWithCoordinates:coordinates count:count];
   

   因此，您可以像这样保存坐标:

   [self writeCoordinates:coordinates count:count file:filename];
   

   其中 writeCooperatives:count:filename: 定义如下:

   - (void)writeCoordinates:(CLLocationCoordinate2D *)coordinates count:(NSUInteger)count file:(NSString *)filename
   {
       NSData *data = [NSData dataWithBytes:coordinates length:count * sizeof(CLLocationCoordinate2D)];
       [data writeToFile:filename atomically:NO];
   }
   

   然后您可以使用以下命令从文件中制作 MKPolygon:

   MKPolygon* poly = [self polygonWithContentsOfFile:filename];
   

   其中polygonWithContentsOfFile定义为:

   - (MKPolygon *)polygonWithContentsOfFile:(NSString *)filename
   {
       NSData *data = [NSData dataWithContentsOfFile:filename];
       NSUInteger count = data.length / sizeof(CLLocationCoordinate2D);
       CLLocationCoordinate2D *coordinates = (CLLocationCoordinate2D *)data.bytes;
   
       return [MKPolygon polygonWithCoordinates:coordinates count:count];
   }
   

2. 或者，您可以以 plist 格式(以人类可读的格式呈现)读取和写入 CLLocationCooperative2D 数组，方法是将上述两种方法替换为:

   const NSString *kLatitudeKey = @"latitude";
   const NSString *kLongitudeKey = @"longitude";
   
   - (void)writeCoordinates:(CLLocationCoordinate2D *)coordinates count:(NSUInteger)count file:(NSString *)filename
   {
       NSMutableArray *array = [NSMutableArray arrayWithCapacity:count];
   
       for (NSUInteger i = 0; i < count; i++)
       {
           CLLocationCoordinate2D coordinate = coordinates[i];
           [array addObject:@{kLatitudeKey:@(coordinate.latitude), kLongitudeKey:@(coordinate.longitude)}];
       }
   
       [array writeToFile:filename atomically:NO];
   }
   
   - (MKPolygon *)polygonWithContentsOfFile:(NSString *)filename
   {        
       NSArray *array = [NSArray arrayWithContentsOfFile:filename];
       NSUInteger count = [array count];
       CLLocationCoordinate2D coordinates[count];
   
       for (NSUInteger i = 0; i < count; i++)
       {
           NSDictionary *dictionary = array[i];
           coordinates[i].latitude = [dictionary[kLatitudeKey] doubleValue];
           coordinates[i].longitude = [dictionary[kLongitudeKey] doubleValue];
       }
   
       return [MKPolygon polygonWithCoordinates:coordinates count:count];
   }
   

显然，您希望添加错误检查代码以确保 writeToFile 和 dataWithContentsOfFile(或 arrayWithContentsOfFile)成功，但是希望这能给您带来启发。