OC learning --- use of @ property and @ synthesize, ocsynthesize

OC learning --- use of @ property and @ synthesize, ocsynthesize

In the previous article, we introduced memory management in OC: Memory:@ Property and @ synthesize

I. @ property keywords

This keyword is used to quickly define an attribute in OC, and it can set some values to achieve a certain effect, such as the reference count problem.

Let's take a look at his usage:

/// Person. h // 25_Property // Created by jiangwei on 14-10-12. // Copyright (c) 2014 jiangwei. all rights reserved. // # import <Foundation/Foundation. h> @ interface User: NSObject {// NSString * _ userName; // NSString * _ passWord ;//...} // The first step is to generate the _ userName attribute // The second step is to automatically generate the set/get method for the _ userName attribute. // is the property referenced in the generated set method? // Three methods of the set Method: // The first method: // normal value assignment // reference operation of the general object type // reference operation of the NSString object type // The first position // atomic: thread-protected, default // nonatomic: the thread is not protected // The second position // assign: direct value assignment, default // retain: Keep object // copy: copy object // The third position // readwrite: generate the get/set method. Default Value: // readonly: generate only the get method.
@property NSString *userName;

@ End

Remember that when we previously defined the attribute {...} and the get/set method may need to be implemented after the definition is complete. Here we use the @ property keyword for definition:

@property NSString *userName;

After the definition, we can use this attribute:

After this method is defined, the set/get method is automatically available for this attribute.

Step 1: generate the _ userName attribute

Step 2: automatically generate the set/get method for the _ userName attribute

Is this definition much more convenient than before?

Next, let's take a look at three other values that can be set:

@property(atomic,retain,readwrite) Dog *dog;

1. value at the first position:

Atomic: thread-protected, default

Nonatomic: The thread is not protected.

2. the value at the second position:

Assign: direct value assignment, default

Retain: indicates the object to be retained. The retain method is automatically called internally and the reference count is + 1.

Copy: copy object

3. value at the third position:

Readwrite: generate the get/set method. The default value is

Readonly: only get methods are generated.

Here is an example:

Main. m

//// Main. m // 25_Property // Created by jiangwei on 14-10-12. // Copyright (c) 2014 jiangwei. all rights reserved. // # import <Foundation/Foundation. h> # import "User. h "# import" Dog. h "// when a class has many attributes, We need to manually write their set/get method //, which is time-consuming, so now you can use @ propertyint main (int argc, const char * argv []) {User * user = [[User alloc] init]; dog * dog = [[Dog alloc] init]; NSLog (@ "count: % ld", [dog retainCount]); [user setDog: dog]; NSLog (@ "count: % ld", [dog retainCount]); return 0 ;}

Running result:

2. @ synthesize keyword

/// Person. m // 25_Property // Created by jiangwei on 14-10-12. // Copyright (c) 2014 jiangwei. all rights reserved. // # import <Foundation/Foundation. h> # import "User. h "// sometimes we don't want to define attributes starting with _ // at this time we can use @ synthesize, to modify the desired attribute name // at this time, the attribute _ userName becomes $ userName @ implementation User @ synthesize userName = $ userName; @ end

Because after @ property is used to define an attribute, if we want to modify the attribute name, we can use the @ synthesize keyword to modify the attribute name.

@synthesize userName = $userName;

Summary

This article mainly introduces the use of two keywords, @ property and @ synthesize, especially the @ property keyword. It is almost used for defining attributes later, which is very convenient.