Question

This is the original codes when I am getting this error

ClassA.h

+(ClassA*)methodA:(NSData*)data;

@property (nonatomic, strong) NSMutableArray    *arr; 
@property (nonatomic, strong) RXMLElement     *rxmlRoot; 

@end

ClassA.m

+(ClassA*)methodA:(NSData*)data {

//NSLog(@"class is %@",[name class]);
ClassA *ClassA   =   [[Stores alloc] init];
arr        =   [NSMutableArray array];
rxmlRoot   = [RXMLElement elementFromXMLData:data];

}

I am reviewing my codes and now I have tow options to fix the code

OptionA

ClassA.h

+(ClassA*)methodA:(NSData*)data;

@property (nonatomic, strong) NSMutableArray    *arr; 
@property (nonatomic, strong) RXMLElement     *rxmlRoot; 

@end

ClassA.m

+(ClassA*)methodA:(NSData*)data {

//NSLog(@"class is %@",[name class]);
ClassA *ClassA   =   [[Stores alloc] init];
ClassA.arr        =   [NSMutableArray array];             <----- this has been modified
ClassA.rxmlRoot   = [RXMLElement elementFromXMLData:data];<----- this has been modified

}

OptionB

ClassA.h

+(ClassA*)methodA:(NSData*)data;

@end

ClassA.m

static RXMLElement    *rxlRoot; <----- this has been added as class variable
static NSMutableArray *arr;     <----- this has been added as class variable

+(ClassA*)methodA:(NSData*)data {

//NSLog(@"class is %@",[name class]);
ClassA *ClassA   =   [[Stores alloc] init];
arr        =   [NSMutableArray array];             
rxmlRoot   = [RXMLElement elementFromXMLData:data];

}

I try either optionA or optionB and the compiler does not complain anything and the codes work properly.

I see many posts following the optionB which create class variables.

Question: is optionA also a good way to follow when we are dealing with class method and class variable as well.

Please advice me on this issue and by the way if I have made mistakes somewhere, please correct me. Thanks

Answer 1

Create a designated initializer with a data parameter. Every class should have a designated initializer.

In your class method call the designated initializer passing in data.

Here is example code:

//ClassA.h
@class RXMLElement;

@interface ClassA : NSObject
+(ClassA*)methodA:(NSData*)data;
-(id)initWithData:(NSData*)data;

@property (nonatomic, strong) NSMutableArray *arr; 
@property (nonatomic, strong) RXMLElement    *rxmlRoot; 

@end

//ClassA.m
@implementation ClassA
@synthesize arr;
@synthesize rxmlRoot;

+(ClassA*)methodA:(NSData*)data {
    return [[ClassA alloc] initWithData:data];
}

-(id)initWithData:(NSData*)data {
    self = [super init];
    if (self) {
        arr      = [NSMutableArray array];
        rxmlRoot = [RXMLElement elementFromXMLData:data];
    }
    return self;
}
@end

ARC is assumed in the example.