[@synthesize in Objective-C]

Foreword

@property can only generate declarations of getter and setter methods, what about the implementation?

1. What is @synthesize?

For example, there is a class

#import
@interface Person : NSObject
{
NSString *_name;
int _age;
float _weight;
}
@property NSString *name;
@property int age;
@property float weight;
@end
@implementation Person

@end

So, can the implementation of getter and setter methods be automatically generated?

1) The role of @synthesize: automatically generate the implementation of getter and setter methods.
2) Syntax: @synthesize @property name;
For example:
@interface Person: NSObject
{
int _age;
}
@property int age;
@end
----------------------
@implementation Person
@synthesize age;
@end

2. What @synthesize does

1. Generate a true private attribute

1) What is a true private property, that is, declared in @implementation,
2) The type of this property is consistent with the @property type corresponding to @synthesize;
3) The name of the property is the same as @The @property name corresponding to synthesize is the same;

For example, this code:
@implementation Person
@synthesize age;
@end
translates to
@implementation Person
{
int age;
}

• (void)setAge:(int)age;
  {
  self->age = age;
  }
• (int)age
  {
  return age;
  }
  @end
  4) Automatically generate the implementation of the setter method
  Implementation method: directly pass the value of the parameter age to it to generateThe private property age;
  5) Automatically generate the implementation of the getter method
  Implementation method: return the value of the private property that it automatically generates

2. How to make @synthesize not automatically generate private attributes, just use our own defined underlined attributes, that's it.

Syntax: @synthesize @property name = existing property name;
Example: @synthesize age = _age;
So, what does this sentence mean?
1) No private properties are generated anymore;
2) The implementation of getter and setter methods is directly generated;
3) How is the setter implemented?Assign the value of the parameter to an existing underscore attribute
For example:

• (void)setAge:(int)age
  {
  _age = age;
  }

4) How is the getter implemented?Returns the value of the existing underscore property directly.

• (int)age
  {
  return _age;
  }

Summary

When using @synthesize, there are a few points to note:
1) If you directly write a @synthesize
For example: @synthesize name;
Then, it automatically generates a private property, and the operation isAutomatically generated private attributes
2) If you specify the attributes of the operation
For example: @synthesize name = _name;
Then, it will not automatically generate private attributes, and the operation is the underlined one we specifiedAttribute;
3) In the implementation of the generated setter method, there is no logic verification, and it is directly assigned.If you want to implement logic verification, you need to write the implementation of the setter method yourself.For example:

• (void)setAge:(int)age
  {
  if(age >= 0 && age <= 120)
  {
  _age = age;
  }
  else
  _age = 18;
  }

4) Batch declaration
For example:
@property float height , weight;
If the types of multiple @property are consistent, they can be declared in batches;

@synthesize name, age, weight, height;
@synthesize name = _name,age=_age,weight=_weight,height= _height;
The types of @synthesize are inconsistent and can also be declared in batches.