OBJECTIVE-C block data type @protocol keywords

Block data type

Block encapsulates a piece of code that can be executed at any time

A block can be used as a function parameter or as a return value of a function and can have an input parameter or return value itself.

Apple's official recommendation is to use block as much as possible in a multi-threaded asynchronous task set traversal collection sort animation transitions with a lot of

Defining a block variable

void (^myblock) ();

Int (^sunblock) (int, int);

Using block encapsulation Code

^ {

NSLog (@"==========");

};

^() {

NSLog (@"=========");

};

^ (int a, int b) {

return a + B;

};

Block access outside variables

External variables can be accessed inside the Block

The outer local variables cannot be modified by default within the block

Add the __block keyword to the local variable and the local variable can be modified inside the block

Defining block types with typedef

typedef int (^myblock) (int, int); ///You can use this type of Myblock to define the block variable

Myblock Block;

Myblock B1, B2;

B1 = ^ (int a, int b) {

return a + B;

};

Myblock B3 = ^ (int a, int b) {

return a + B;

};

@protocol keywords

Can be used to declare a whole bunch of methods (cannot declare member variables)

As long as a class complies with this agreement, it is equivalent to having all the method declarations in this agreement.

As long as the parent adheres to a protocol, the subclass also adheres to the

Protocol writing format

@protocol Agreement name <NSObject>

Method declaration List

@end

A class adheres to the agreement

@interface Class Name: Parent class < protocol name 1, ...>

@end

Agreement Compliance Agreement

A protocol that complies with another protocol can have all method declarations for another protocol

@protocol Agreement name < Agreement name 1, ...>

Method declaration List

@end

Keywords for method declarations in the Protocol

@required require implementation does not implement there will be warnings (default)

@optionnal Optional Implementation

Base protocol

NSObject is a base class any other class will eventually inherit it

There is also a NSObject-based protocol that declares many of the most basic methods, such as description retain release, and so on.

It is recommended that each new protocol complies with the NSObject base protocol

When defining a variable, limit the object to which the variable is saved to comply with a protocol

Class name < protocol name > * variable name;

id< protocol name > variable name;

nsobject<myprotocol> *obj = [[NSObject alloc] init];

@property (nonatomic, strong) id<myprotocol> obj;

If the corresponding protocol compiler is not followed, the error will be

OBJECTIVE-C block data type @protocol keywords