Property in the Objective-c

Where the property can be declared

Property can be declared in the Class Interface section and class extension and protocol

The visibility of the property

The property in Objective-c is actually the getter and setter method. The property of a class can be accessed externally, primarily to see if the property declaration of the class can be externally visible. For example, there is a class x whose. h and. m files are as follows:

 
 
//X.h

#import <Foundation/Foundation.h>

@interface X : NSObject

@end
//X.m

#import "X.h"

@interface X ()

@property (assign, nonatomic) int i;

@end

@implementation X



@end

If you access the property declared in X.M in the main function, you will get an error:

//main.m

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


int main (int argc, const char * argv []) {
     @autoreleasepool {
        
         X * x = [X new];
         x.i = 2; // error, property i is not visible
        
     }
     return 0;
} 

However, if we move the class extension in the East X.h, then the main function can see the declaration of property I, will not error. Alternatively, you can declare the setter method of property I in the interface section of X.h, because the main function accesses the actual setter method of property I, and after declaration, the setter method is visible to the main function. , so there is no error.

Name of property Composition instance variable

There are 3 cases in the property composition instance variable:

1) Do not use the @synthesize instruction, at this time the composite instance variable name is underlined with the property, that is _property

2) using only the @synthesize property name, the instance variable of the composition is the same as the property name at this time

3) Use @synthesize property name = Instance name, then the instance name of the composition is the specified name

When does the instance variable not be synthesized for the property

If you customize the Getter,setter method for a readwriteproperty or customize the Getter method for a ReadOnly property, the compiler does not automatically synthesize the corresponding instance variable. Unless displayed using @synthesize property name or @synthesize property name = Instance Name

Accessibility of an instance variable of a composition

The instance variables of the composition are private.

Default attribute for property

The default attribute for the property is strong (for reference types), Atomic,readwrite

Property in the Objective-c