iOS pointer to function and block

One: block Basics

Block Basics

Basic concept: block is used to save a piece of code; ^: is a block sign like *: A sign of a pointer

Features: 1: Save a piece of code;

2: can have parameters and return values;

3: Can be passed as a function parameter;

and code blocks, the code in the code will be executed automatically, block the code to be called manually;

Two: Common data types, pointers to functions, and the definition of block

1: Basic Data type:

For example:int a = 10;

Format: data type variable name = value;

2: Pointer to function: can be modeled on the definition of the underlying data type above

For example:void (*p) () = function; (Funciton is a well-defined function)

Format: function type * pointer variable name = function name;

Note: Since the P pointer is a pointer to a function, the red parentheses in (*p)() must be there, because the function itself is to be parameterized, even if no parameters are written ();

If the function p points to has parameters:int (*pp) (int, int) = SUM;

To invoke a pointer to a function:

No reference: P ();

parameter: int sum = PP (2,3);

The definition and use of 3:block, and the pointer to the function of the format very much like

For example:void (^firstblock) () = ^(){...   Code ...}; Description: The blue parenthesis can not be written, the parameters must be written when

Format:block type ^block name = ^{Code snippet};

Parameter block:int (^multiblock) (int, int) = ^ (int a, int b) {

return a * b;

};

　　Call BLOCK: No parameter:Firstblock ()

parameter: int result = Multiblock (2, 3);

　　

// Note: Functions and blocks that point to pointers can be defined in steps like basic data types: int (^multiblock) (intint);         = ^ (intint  b) {        return A * b;    };

Example code:

1 //function Definition2 intSumintAintb)3 {4NSLog (@"a+b=%d", A +b);5     return 2;6 }7 8 voidlogsome ()9 {TenNSLog (@"I am the output function of void type"); One } A  - intMain () - { the     /** * 1: Definition of basic data type * **/ -     intA =Ten; -     //1.1 Define and assign values first -     intb; +b = -; -      +     /** * 2: pointer to function * **/ A      at     //2.1: Pointer to the sum (int a, int b) function with parameters -     int(*p) (int,int) =sum; -     //2.2: Pointer to parameterless function logsome () function -     void(*LOGP) () =Logsome; -      -     //call a pointer function to a function inP2,3); - Logp (); to      +     /** * 3:block definition and use * **/ -      the     //3.1: Block definition with no parameters *     void(^firstblock) () = ^{ $         Panax NotoginsengNSLog (@"Note: (^multiblock) (), here the parentheses must be written, regardless of whether there are parameters"); -          theNSLog (@"the latter side of the \"^(){ \"the parentheses can not be written"); +     }; A      the     //Call of Block + Firstblock (); -      $     //3.2 block with parameters and return values $     int(^multiblock) (int,int) = ^(intAintb) { -         returnAb; -     }; the      -     //Call BlockWuyi     intresult = Multiblock (2,3); theNSLog (@"%d", result); -      Wu}

Three: Using a typedef-defined block

Using typedef can simplify the tedious block definition

For example: typedef void (^myblock) (); You can then create a block with Myblock, create a format like class to create the object

　　

// define block with typedef void (^myblock) (); int Main () {    //  use a custom block to create a block    myblock myblock = ^{        NSLog ( @"" );    };    }

Four: block and pointers to functions as function arguments

Using typedef to make the cumbersome block simple, this block becomes a type that can create objects like classes, and pointers to functions can also

//defining pointers to functions with typedef definitionstypedefvoid(*Tp) ();//define block with typedeftypedefvoid(^Myblock) ();voidLogsome () {NSLog (@"I am the output function of void type");}//pointer to function as argumentvoidtest1 (Tp p) {p ();}//block as a parameter of a functionvoidtest2 (myblock MB) {MB ();}intMain () {//pointer to function definitionTp MyP =Logsome;        Test3 (MyP); //Define blockMyblock MB = ^{NSLog (@"Block Output");    }; Test4 (MB);}

Note: C language functions and methods in OC are somewhat different, C language function parameters to write block the latter pointer to the function, you must first use the TypeDef bar block or pointer to the function of pointers defined as a type, and then can be passed in the parameters of the function;

In the OC method definition, block can be used as the parameter directly;