iOS Learning-9-1. Block Getting Started

Video from Li Mingjie.

Block is used to save a piece of code

Block's logo: ^

block is like a function :

1). Can save code 2). Has a return value of 3). Tangible parameters

Temp1: Block with no return value, no formal parameters

If the block has no formal parameters, you can omit ()

void (^myblock) () = ^{        NSLog (@ "----------");        NSLog (@ "----------");    };     // use block variables to invoke code    inside block Myblock ();

Temp2: There are return values, tangible parameters

int (^sumblock) (int,int) = ^ (int A,int  b) {        return a +b;    }    ; // return value    int c = sumblock (1,1);    NSLog (@ "%d", c);

Temp 3: Output n horizontal lines with a block

void (^lineblock) (int) = ^ (int  n) {        for (int1; i < n; i++) {            NSLog ( @"-------");        }    };     // no return value, plus argument    of type int Lineblock (5);

Temp 4:

 __block int  a = 10      void  (^block) (); Block  = ^{ /*   inside the block can access the variables outside by default, the block inside cannot modify the outside local variables to the local variable plus the __block keyword, this local variable can be modified within the block */  a  =  ; NSLog ( @ " %d   "    ,a);    }; Block ();   

Temp 5: defining block types with typedef

//type + variableMyblock Sumblock; Sumblock= ^(intAintb) {        returnA +b;    }; Sumblock (Ten,9); //SubtractionMyblock Minusblock; Minusblock= ^(intAintb) {        returnAb;    }; Minusblock (Ten,9); //multiplicationMyblock Multipblock; Multipblock= ^(intAintb) {        returnAb;    }; Multipblock (Ten,9); //DivisionMyblock Divideblock; Divideblock= ^(intAintb) {        returnAb;    }; Divideblock (Ten,2); NSLog (@"\ n%d \ n%d \n%d \ n%d", Sumblock (Ten,9), Minusblock (Ten,9), Multipblock (Ten,9), Divideblock (Ten,2));

Summarize:

1. How to define a block variable

int (^sumblock) (int,int); void (^myblock) ();

2. How to use block encapsulation code

^ (int A,int  b) {        return  A- b;    };     // No parameters    ^() {        NSLog (@ "-----");    }     // no return value    ^{        NSLog (@ "-----");    }

3. Block access outside variables

1.block internal can access the outside of the variable 2. By default, the outer local variables cannot be modified inside the block
3. Add the __block keyword to the local variable and the local variable can be modified inside the block

4. Defining block types with typedef

int (^myblock) (int,int);     // You can then use this type of Myblock to define the block variable     Myblock block;    Myblock b1,b2;     = ^ (int A,int  b) {    return a +b;    }    ; = ^ (int A,int  b) {    return a +B;    };

iOS Learning-9-1. Block Getting Started