Basic review: Get methods and Set methods (inheritance polymorphism for classes)

Basic review: Get methods and Set methods

When you define a class member variable, you can define it in @interface, or you can define it in @implementation:

Declared in @interface, the state of the member variable is protected, i.e. "@protected";

Declared in @implementation, the state of the member variable is private, that is, "@private"

Outside of the class, the member variables cannot be accessed directly, and can only be accessed externally if the member variable is modified to @public.

When using @public, Access member variables using "-", such as:

time->hour=25;

However, the use of @public is risky (as the above code sets hour to 25, actually only 24 hours), so the general access member variable uses the Get and set methods;

Declaration of the Get method:

-(int) hour;    Get method, naming rule: The return type is the type of the member variable, the method name is the member variable name

Declaration of the Set method:

-(void) Sethour: (int) Newhour    //set method, naming rule: The return type is void, the method name is the first letter of the set+ member variable name, with a parameter, the type of the parameter type bit member variable

Implementation of the Get method:

-(int) hour{    return hour;          }

The implementation of the Set method:

-(void) Sethour: (int) newhour{    if (newhour>24| | NEWHOUR<0)    //filter for unreasonable values    {         hour=0;    }    Hour=newhour;}

After you use the Get method and the Set method, you can use the "." Syntax Access member variables:

time.h=22;

“.” The syntax can call the Get method and the set method automatically, when assigning a value to the member variable, the Set method is called automatically, and when the member variable is obtained, the Get method is called automatically;

time.h=22;    Automatic call Set method assignment Xiaoshi=time.h    //Auto Call get method to get time.h value

In Objective-c, two statements are provided to automatically generate the Get and set methods:

@property: can only be used in @interface to automatically generate corresponding get and set method declarations for member variables

@synthesize: can only be used in @implementation to automatically generate corresponding get and set method implementations for member variables

For example:

@property int hour; @synthesize hour;

Advanced: Characteristics of @property and @synthesize

1. After using @property and @synthesize, you can still use Sethour: To access member variables:

Time *tm=[time new]; [TM Sethour:22];

2. After using @property and @synthsize, although the get and set methods are automatically generated, you can still redefine the set and get methods yourself, and the redefined method overrides the auto-generated method, which is convenient for filtering data and setting certain rules.

3. When the Get and set methods are automatically generated using only @property, @property automatically generates a member variable named "_ Name":

@property int hour; Automatically generate member variable "_hour"

At this point, the @property automatically performed 3 operations:

1) generate a member variable named "_hour" (after 4.6 version of Xcode)

2) generate a declaration of the corresponding get and set methods for "_hour"

3) Bit "_hour" generates the corresponding get and set method implementations

Therefore, after using @propery, you can omit the member variable declaration from "{}" because it is automatically generated.

[Email protected] hour, will look for instance variable "hour", if not found, automatically generate a "hour" member variable

Using: @synthesize Hour=_hour, you can associate "hour" with "_hour" and no longer generate "hour" member variables

5. In the set and get methods, use "self." is not allowed because "self." The call is the method itself, which forms a dead loop.

• Member variables if external access is not required, use curly braces in the same way as before

Basic review: Get methods and Set methods (inheritance polymorphism for classes)