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，以便以后检索。绘制路径的大多数代码都基于示例代码Breadcrumb。

现在我正在添加功能以保存绘制的叠加层。什么是最好的方法呢？我可以使用CoreData，但我不打算对绘制的叠加做很多事情，而不是稍后再检索它。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。但是，我似乎做错了什么。

@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

我将CrumbPath对象保存为“crumbs”，如下所示：

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));

再次构建路径：

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', reason: '-[NSConcreteData isEqualToString:]: unrecognized selector sent to instance

Answer 1

就个人而言，我倾向于这样做：

首先，我倾向于保存我传递给CLLocationCoordinate2D实例方法MKPolygon的{{1}}坐标的C数组（而不是polygonWithCoordinates C数组）。如果你宁愿使用MKMapPoint，你可以调整这段代码，但我更喜欢一种我可以在外部检查并理解的格式（即MKMapPoints的纬度和经度值）。所以，我们假设您使用如下代码行创建CLLocationCoordinate2D：
```
MKPolygon
```
你可以这样保存坐标：
```
MKPolygon* poly = [MKPolygon polygonWithCoordinates:coordinates count:count];
```
[self writeCoordinates:coordinates count:count file:filename];的定义如下：
```
writeCoordinates:count:filename:
```
然后，您可以使用以下命令从文件中创建- (void)writeCoordinates:(CLLocationCoordinate2D *)coordinates count:(NSUInteger)count file:(NSString *)filename { NSData *data = [NSData dataWithBytes:coordinates length:count * sizeof(CLLocationCoordinate2D)]; [data writeToFile:filename atomically:NO]; }
```
MKPolygon
```
其中MKPolygon* poly = [self polygonWithContentsOfFile:filename];定义为：
```
polygonWithContentsOfFile
```
或者，你可以用plist格式读取和写入- (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]; }数组（以人类可读的格式呈现），方法是将上述两种方法替换为：
```
CLLocationCoordinate2D
```

显然，您需要添加错误检查代码，以确保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]; }和writeToFile（或dataWithContentsOfFile）成功，但希望这能为您提供这个想法。

如何将MKOverlay对象存储到文件以便以后检索

1 个答案: