自定义注释与自定义变量

Question

我目前有一个地图视图控制器，其中我添加批注基于一些分析的JSON数据。

我想从这个json数据传递一个值到下面的segue，他们想要做的是为每个注解添加一个自定义变量（venueId），所以当它被按下时，我可以设置一个全局下一个赛格通过某种逻辑获得的价值。

然而一切我曾尝试已经导致了venueId NULL值，我的代码如下：

MyLocation.H

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

@interface MyLocation : NSObject <MKAnnotation>{ 

    NSNumber *venueId; 
} 

@property (nonatomic,readonly) NSNumber *venueId; 

- (id)initWithName:(NSString *)name address:(NSString *)address coordinate:(CLLocationCoordinate2D)coordinate venueId:(NSNumber*)venueId; 


@end 

MyLocation.M

#import "MyLocation.h" 
#import "GlobalData.h" 

@interface MyLocation() 

@property (nonatomic,copy) NSString *name; 
@property (nonatomic,copy) NSString *address; 
@property (nonatomic,assign) CLLocationCoordinate2D coordinate; 


@end 
@implementation MyLocation 

@synthesize venueId = _venueId; 

- (id) initWithName:(NSString *)name address:(NSString *)address coordinate:(CLLocationCoordinate2D)coordinate venueId:(NSNumber*)venueId{ 

    if ((self = [super init])) { 

     self.name = name; 
     self.address = address; 
     self.coordinate = coordinate; 
     _venueId = self.venueId; 

    } 
    return self; 

} 

- (NSString *)title{ 
    return _name; 
} 

- (NSString *)subtitle{ 
    return _address; 
} 


- (CLLocationCoordinate2D)coordinate{ 
    return _coordinate; 
} 

- (NSNumber *)venueId{ 
    return _venueId; 
} 


- (void)mapView:(MKMapView *)mapView annotationView:(MKAnnotationView *)view calloutAccessoryControlTapped:(UIControl *)control{ 

    NSLog(@"THE CALL OUT has been pressed"); 

} 

@end 

绘图我的MapViewController.M中的场地

//根据数据传递绘制场地编辑在

- (void)plotVenuePositions{ 

    for (id<MKAnnotation> annotation in _mapView.annotations){ 
     // start fresh and remove any annotations in the view 
     [_mapView removeAnnotation:annotation]; 
    } 

    for (NSDictionary *row in [[GlobalData sharedGlobalData]venuesArray]){ 

     NSNumber *venueId = [row objectForKey:@"v_id"]; 
     NSString *venueName =[row objectForKey:@"v_name"]; 
     NSNumber *venueLat = [row objectForKey:@"v_lat"]; 
     NSNumber *venueLon = [row objectForKey:@"v_lon"]; 
     NSString *venueTown = [row objectForKey:@"t_name"]; 

     // create co-ord 
     CLLocationCoordinate2D coordinate; 
     // set values 
     coordinate.latitude = venueLat.doubleValue; 
     coordinate.longitude = venueLon.doubleValue; 
     // create annotation instance 
     MyLocation *annotation = [[MyLocation alloc]initWithName:venueName address:venueTown coordinate:coordinate venueId:venueId]; 
     // add annotation 
     [_mapView addAnnotation:annotation]; 
     NSLog(@"VNEU ID IS %@",venueId); 
     NSLog(@"ANNOTATION name is %@", annotation.title); 
     NSLog(@"ANNOTATION subtitle is %@", annotation.subtitle); 
     NSLog(@"ANNOTATION description is %@", annotation.description); 
     NSLog(@"ANNOTATION venue ID IS %@", (MyLocation *)annotation.venueId); 
    } 

} 

最后在MapViewController.M

注释检查

-(MKAnnotationView *)mapView:(MKMapView *)mapView viewForAnnotation:(id<MKAnnotation>)annotation{ 
static NSString *identifier = @"MyLocation"; 
if ([annotation isKindOfClass:[MyLocation class]]) { 

MKAnnotationView *annotationView = (MKAnnotationView *) [_mapView dequeueReusableAnnotationViewWithIdentifier:identifier]; 
if (annotationView == nil) { 
    annotationView = [[MKAnnotationView alloc]initWithAnnotation:annotation reuseIdentifier:identifier]; 
    annotationView.enabled = YES; 
    annotationView.canShowCallout = YES; 
    annotationView.image = [UIImage imageNamed:@"pin_orange.png"]; 
    // set the cell to have a callout button 
    annotationView.rightCalloutAccessoryView = [UIButton buttonWithType:UIButtonTypeDetailDisclosure]; 
} 
else{ 
annotationView.annotation = annotation; 
} 
return annotationView; 
} 
return nil; 
} 

Answer 1

在initWithName方法，这行：

_venueId = self.venueId; 

不设置当前位置的场地ID发送到init方法的参数值venueId。
它将其设置为venueId的当前位置的属性的值。

由于该属性值由_venueId支持，因此该行实际上将其设置为等于自身，并且由于它最初为空，因此它保留为空。

行应该是：

_venueId = venueId; 

，或者如果你没有使用ARC：

_venueId = [venueId retain]; 

这一行，但是，给你一个编译器警告“本地变量隐藏实例变量“。这是因为方法参数名称与属性名称相同。

虽然变化会工作，除去编译器警告，改变方法参数的名称比其他东西venueId（如iVenueId），然后改变的线是：

_venueId = iVenueId;