OBJECTIVE-C Basic Notes (2) @property and @synthesize

First post the code in the previous article using @property and @synthesize, and then explain the usage and meaning of these two keyword, such as the following code:

Person.h file

#import <Foundation / Foundation.h>

@interface Person: NSObject {
     int _age; // can be accessed by subclasses
     // The system will help us generate a default int _no private variable (not accessible by subclasses)
}

@property int age;
@property int no;

// Write a constructor yourself
-(id) initWithAge: (int) age andNo: (int) no;

@end

Person.m File

#import "Person.h"

@implementation Person

// You don't need to write the following two sentences above Xcode 4.5 (can be omitted, and the default is _age and _no)
// @ synthesize age = _age; // declared as protected
// @ synthesize no = _no; // The default is private

-(id) initWithAge: (int) age andNo: (int) no {
     if (self = [super init]) {
         _age = age;
         _no = no;
     }
     return self;
}

-(NSString *) description {
     return [NSString stringWithFormat: @ "age is% i and no is% i", _age, _no];
}

@end

MAIN.M file

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

int main (int argc, const char * argv []) {
     @autoreleasepool {
         Person * person = [[Person alloc] initWithAge: 15 andNo: 2];
        
         NSLog (@ "age is% i and no is% i", person.age, person.no);
        
         [person setNo: 3];
         NSLog (@ "no is% i", [person no]);
         //% @ represents printing an OC object
         NSLog (@ "% @", person);
     }
     return 0;
}

Output Result:

2014-11-12 21:53:15.406 firstocproj[826:47802] is 2

2014-11-12 21:53:15.407 firstocproj[826:47802] No is 3

2014-11-12 21:53:15.408 firstocproj[826:47802] is 3

You can see that the above code is a lot more concise, the function of @property is equivalent to the declaration of member variables, the role of @synthesize is equivalent to the standard implementation of the member variable setter and getter.

It is important to note that:

1, in Xcode4.5 above can not write @synthesize attribute (compiler Default).

2, such a writing can be used in the previous wording (old writing) cross-use.

3, assume that the setter or getter method has special treatment. can use the old notation (the compiler will not help us by default).

4. If you do not explicitly declare a variable, the default is to generate a private member variable (it cannot be used as a quilt, such as the _no above).

Here we will make the above code a little simpler:

Person.h

#import <Foundation/Foundation.h>

@interface Person : NSObject

@property int age;
@property int no;

@end

Person.m

#import "Person.h"

@implementation Person

@end

Main.m

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

int main(int argc, const char * argv[]) {
    @autoreleasepool {
        Person *person = [Person new];
        [person setAge:20];
        [person setNo:3];
        NSLog(@"age is %i and no is %i", person.age, person.no);
    }
    return 0;
}

Output Result:

2014-11-12 22:14:44.002 firstocproj[849:52867] is 3

Note: My compiler Xcode is more than 4.5. So you can omit the @synthesize attribute in person.m.

Here has to be right OC and Xcode compiler exclamation. So convenient and easy to use tools I really was the first time to see, silently praise a bit.

OBJECTIVE-C Basic Notes (2) @property and @synthesize