ios - 如何在单例 NSMutableArray 中添加对象

Question

我用来存放从服务器下载的数组数据。但是我不能将它们保存在单例数组中。

似乎无法访问该对象。

为什么 ulatitude、ulongitude、uaccuracy、uplacename 为 nil？...

在.h文件中

#import <Foundation/Foundation.h>
@interface LocationData : NSObject
{
    NSMutableArray *ulatitude;
    NSMutableArray *ulongitude;
    NSMutableArray *uaccuracy;
    NSMutableArray *uplacename;
}
@property (nonatomic, retain) NSMutableArray *ulatitude;
@property (nonatomic, retain) NSMutableArray *ulongitude;
@property (nonatomic, retain) NSMutableArray *uaccuracy;
@property (nonatomic, retain) NSMutableArray *uplacename;
+ (LocationData*) sharedStateInstance;
@end

在 .m 文件中

#import "LocationData.h"

@implementation LocationData

@synthesize uaccuracy;
@synthesize ulatitude;
@synthesize ulongitude;

+ (LocationData*) sharedStateInstance {
        static LocationData *sharedStateInstance;

        @synchronized(self) {
            if(!sharedStateInstance) {
                sharedStateInstance = [[LocationData alloc] init];
            }
        }
        return sharedStateInstance;
}
@end

使用

[manager POST:urlStr parameters:params success:^(AFHTTPRequestOperation *operation, id responseObject)
    {

                 NSLog(@"%@",responseObject);

                 // json response array
                 if ([responseObject isKindOfClass:[NSArray class]]) {

                     NSArray *responseArray = responseObject;
                     NSDictionary *responseDict = [[NSDictionary alloc] init];

                     LocationData* sharedState = [LocationData sharedStateInstance];

                     for(NSUInteger i=0; i < responseArray.count; i++)
                     {
                         responseDict = [responseArray objectAtIndex:i];

                         double dlat = [[responseDict objectForKey:@"lat"] doubleValue];
                         double dlng = [[responseDict objectForKey:@"lng"] doubleValue];

                          [[sharedState ulatitude] addObject:[NSString stringWithFormat:@"%f",dlat]];
                          [[sharedState ulongitude] addObject:[NSString stringWithFormat:@"%f",dlng]];
                          [[sharedState uaccuracy] addObject:[responseDict objectForKey:@"rad"]];
                          [[sharedState uplacename] addObject:[responseDict objectForKey:@"place_name"]];
}

Answer 1

你总是需要初始化你的数组。在尝试向它们添加内容之前，您应该先做一些事情:

arrayName = [[NSMutableArray alloc] init];

否则你总是会出错，因为它们还没有被初始化。

在您的情况下，您应该像这样覆盖 LocationData init 函数:

- (instancetype)init {
    self = [super init];
    if (self) {
        self.yourArrayName = [[NSMutableArray alloc] init];
        // And so on....
    }
    return self;
}