Objective-C - 接收器类型'NSInteger'（又名'long'）不是Objective-C类和接收器类型'NSDecimal'不是Objective-C类

Question

I am getting the errors in title and I have no idea why....

.h

@interface ItemData : NSObject

@property (nonatomic,assign) NSInteger tagId;
@property (nonatomic,strong) NSMutableString *deviceId;
@property (nonatomic,strong) NSDecimal *latitude;
@property (nonatomic,strong) NSDecimal *longitude;


@end

.m

#import <Foundation/Foundation.h>
#import "ItemData.h"

@implementation ItemData

-(id)init
{
    if(self = [super init])
    {
        //TODO: Fix Commented out items

        _tagId = [[NSInteger alloc] init];
        _deviceId = [[NSMutableString alloc] init];
        _latitude = [[NSDecimal alloc] init];
        _longitude = [[NSDecimal alloc] init];

    }
    return self;
}

@end

I dont understand what I am doing wrong...can someone help me out?

Answer 1

NSInteger and NSDecimal are no classes, but the type of scalars. You cannot sent messages to "objects" (in the sense of C, not in the sense of OOP) of this type. Therefore you do not construct them with +alloc and -init… .

You have two possibilities:

A. Use (OOP) objects instead of scalars

@property (nonatomic,assign) NSNumber *tagId;
@property (nonatomic,strong) NSDecimalNumber *latitude;

Then you can assign references to objects as usual:

_tagId = @0; // Or whatever you want.
_latitude = [NSDecimalNumber zero];

B. Simply assign a value

_tagId = 0; // Or whatever you want. There is no nil for integers

This works good for integers, but bad for decimals, since they are a struct with private components and there is no function to create them. However, you can create an NSDecimalNumber instance object (as in A.) and get the decimal value with -decimalValue .

_latitude = [[NSDecimalNumber zero] decimalValue];

The usage of NSDecimal seems to be erroneous for me. Why do you want to use it? Usually longitude and latitude are double , another scalar type, which can be treated as integers with values. Decimal floating point objects are for use in finance software.

Answer 2

NSInteger is

typedef long NSInteger;

That should explain "NSInteger (aka 'long')" and it is equivalent 64-bit long (long int) C data type. It is not an OC class, that's why you can't do (+)alloc and (-)init.