The SEL and ID of OC

SEL s2 = @selector (eat:);

[Ani performselector:s2 withobject:@ "a lollipop stained with Baba"];

[Ani performselector: @selector (eat:andfoodname:)

Withobject:@ "The monitor raises the vicious dog" withobject:@ "a piece stained with Baba Lollipop"];

SEL (is a type that contains an address)

ID Type:

Both NSObject and ID types can point to any object

NSObject Compile-time check (requires coercion of type conversions)

ID does not require coercion type conversion, ID can be used directly

The compiler sees the ID type, which is considered to be a dynamic type, not a check type

23) Polymorphism:

Parent class cannot access child class methods

The concept of polymorphism: the ability of different objects to respond to the same name in their own way is called a polymorphic

Show: The pointer of the parent class points to the object of the child class

Conditions of polymorphism: 1) having an inheritance relationship

2) There is a method override (subclass overrides the parent class with the same name method)

Use of polymorphism Note:

1) Use a subclass method if this method is not in the parent class, use subclasses to force type conversions

How to get the class object:

Class object belongs to class type

1) Get through the instance object

Class C1 = [D class];

Class C2 = [D1 class];

2) Get class object by class name

Class C3 = [Dog class];

NSLog ("%p", C3);

24) Construction Method:

The inner part of the new method calls two method classes to complete 3 things:

1) Use the Alloc method to allocate storage space (returns the allocated object);

2) Initialize the object using the Init method;

3) Return the first address of the object

Init is an object method

[Person Alloc], memory has been cleared 0 (where the properties are initialized by 0)

OC constructs the method to learn which content:

Learn how to override the construction method so that after the object is created, there is an initial value

Super refers to the parent class object

25) Custom Construction method:

1) is an object method:

2) Return is ID type (instancetype)

3) The method name must be Initwith

-(Instancetype) Initwithname: (NSString *) name andage: (int) age{...}

Person *P1 = [Person alloc] initwithname:@ "Zhang San Fung" Andage:

The SEL and ID of OC