将 Parse PFGeoPoints 数组显示为地图注释错误

Question

我试图在地图上显示存储在 NSArray 中的对象。在执行获取用户 2 英里范围内位置的方法后，对象从名为 Affiliates 的 Parse.com class 中提取。我已经使用 NSLog 来确认查询正在正确执行，所以我知道提取也正在正确执行。

当我尝试运行应用程序时，我在 for(NSDictionary) 部分抛出错误并且应用程序冻结。错误状态 "Thread 1: EXC_BAD_ACCESS (access code 1, address 0x80120)" 在咨询 Google 后，我发现这是某种类型的内存分配问题，但我不知道它为什么会发生或如何修复它。

#import "ViewController.h"
#import "MapAnnotation.h"

@import CoreLocation;

@interface ViewController () <CLLocationManagerDelegate>

@property (nonatomic,strong) NSArray *affiliates;

@end

@implementation ViewController

- (void)viewDidLoad {


    [super viewDidLoad];

    // Ask for authorization to collect location from user
    CLLocationManager * locationManager = [[CLLocationManager alloc] init];
    // Check for iOS 8. Without this guard the code will crash with "unknown selector" on iOS 7.
    if ([locationManager respondsToSelector:@selector(requestWhenInUseAuthorization)]) {

        locationManager.delegate = self;
        locationManager.distanceFilter = kCLDistanceFilterNone;
        locationManager.desiredAccuracy = kCLLocationAccuracyBest;
        [locationManager startUpdatingLocation];
        [locationManager requestWhenInUseAuthorization];
    }

    //Set map options
    self.mapView.showsUserLocation = YES;
    self.mapView.delegate = self;
    self.mapView.scrollEnabled = YES;
    self.mapView.zoomEnabled = YES;
    self.mapView.userTrackingMode = YES;

    // Store the user's location as a Parse PFGeoPoint and call the fetchAffiliatesNearPoint method
    [PFGeoPoint geoPointForCurrentLocationInBackground:^(PFGeoPoint *geoPoint, NSError *error) {
        if (!error) {
            [self fetchAffiliatesNearPoint:geoPoint];
            NSLog(@"Got User Location! %@", geoPoint);
        }
    }];

    /* This is where I am having issues

    for(NSDictionary *affiliates in affiliates) {
        CLLocationCoordinate2D annotationCoordinate = CLLocationCoordinate2DMake([affiliates[@"latitude"] doubleValue], [affiliates[@"longitude"] doubleValue]);

        MapAnnotation *annotation = [[MapAnnotation alloc] init];
        annotation.coordinate = annotationCoordinate;
        annotation.title = affiliates[@"name"];
        annotation.subtitle = affiliates[@"url"];
        [self.mapView addAnnotation:annotation];
    }

*/

}


//Fetch an array of affiliates that are within two miles of the user's current location.
- (void)fetchAffiliatesNearPoint:(PFGeoPoint *)geoPoint
{

    PFQuery *query = [PFQuery queryWithClassName:@"Affiliates"];
    [query whereKey:@"geometry" nearGeoPoint:geoPoint withinMiles:2.0];
    [query findObjectsInBackgroundWithBlock:^(NSArray *objects, NSError *error) {
        if (!error)
        {
            self.affiliates = objects;
            NSLog(@"Nearby Locations %@", _affiliates);
        }
    }];
}


-(void)mapView:(MKMapView *)mapView didUpdateUserLocation:(MKUserLocation *)userLocation
{


    //Zoom map to users current location
    if (!self.initialLocation) {
        self.initialLocation = userLocation.location;
        MKCoordinateRegion mapRegion;
        mapRegion.center = mapView.userLocation.coordinate;
        mapRegion.span.latitudeDelta = .025;
        mapRegion.span.longitudeDelta = .025;

        [mapView setRegion:mapRegion animated: YES];
        }

}
@end

Answer 1

如果要将自定义对象添加到 MapKit 地图，您的自定义对象必须符合 MKAnnotation 协议。只有一个属性您需要实现才能使您的对象符合协议：

@property (nonatomic, readonly) CLLocationCoordinate2D coordinate;

其余属性（例如 title 和 subtitle）和方法是可选的。

您需要做的就是在 PFGeoPoint 上创建一个类别（假设您正在使用 Objective-C）并为 coordinate 属性实施 getter。

PFGeoPoint+Annotation.h

@interface PFGeoPoint (Annotation) <MKAnnotation>

@end

PFGeoPoint+Annotation.m

@implementation PFGeoPoint (Annotation)

- (CLLocationCoordinate2D)coordinate {
    return CLLocationCoordinate2DMake(self.latitude, self.longitude);
}

@end

最后，要将其添加到地图，您将使用：

- (void)addAnnotation:(id <MKAnnotation>)annotation;

例如：[mapView addAnnotation:geoPoint];

Answer 2

我也没有使用过 Parse，但有几个明显的问题可能会有所帮助：

这行没有意义：
```
for(NSDictionary *affiliates in affiliates)
```
这里，in之后的affiliates指的是locally声明的字典变量，not指的是属性同名变量。由于局部变量没有初始化引用并且指向一些随机内存，所以你得到 EXC_BAD_ACCESS。使用 self.affiliates 明确引用属性.

此外，非常将循环变量命名为与它正在循环的数组相同的名称会令人困惑。您正在遍历 "affiliates"（复数）数组。该数组包含字典，每个字典都是 "affiliate"（单数）。将字典变量命名为 affiliate（单数）会更容易混淆。示例：
```
for (NSDictionary *affiliate in self.affiliates)
```
同时将循环内剩余的引用从 affiliates 更改为 affiliate。
目前，self.affiliates 上的循环是在 geoPointForCurrentLocationInBackground 开始后立即完成的。 geoPointForCurrentLocationInBackground 似乎是异步的，这意味着 self.affiliates 上的循环将在 geoPointForCurrentLocationInBackground 实际设置属性之前执行。

不要在 geoPointForCurrentLocationInBackground 开始后立即在 viewDidLoad 中循环 self.affiliates，而是将循环移动到 findObjectsInBackgroundWithBlock 的完成块内（之后 self.affiliates 已设置）。示例：

[query findObjectsInBackgroundWithBlock:^(NSArray *objects, NSError *error) { if (!error) { self.affiliates = objects; NSLog(@"Nearby Locations %@", _affiliates); for(NSDictionary *affiliate in self.affiliates) { ... } } }];

将 Parse PFGeoPoints 数组显示为地图注释错误

Display an array of Parse PFGeoPoints as Map Annotations Error

ios

objective-c

parse-platform

nsarray

mkannotation