The first knowledge of block

Description of block :

Block is a new syntax structure after iOS4.0, also known as "Closure (closure)".

SDK4.0 's new API uses blocks heavily.

Block is an anonymous function code block that can be passed as a parameter to other objects.

Object

Method

Block Blocks {

... Code

};

}

use of block:Statement of the 1.block

Defining types, defining variables

Int (^sum) (int a, int b);

creation of 2.block

Implement block

sum = ^ (int a, int b) {

return a+b;

};

3.block of Calls

1 Direct call

int sum1 = ^ (int a,int b) {

return a+b;

} (5,9);

NSLog (@ "%d", sum1);

2 called by the block variable

int sum2 = SUM (20,39);

NSLog (@ "%d", sum2);

4. Block in many cases#pragma Mark Creatkindsofblock

-(void) creatkindsofblock{

1---No parameter, no return value

^(){

NSLog (@ "No parameter, no return value");

}();

2---with parameters, no return value

^ (int a,nsstring *text) {

NSLog (@ "%d,%@", a,text);

} (88,@ "parameter, no return value");

3---No parameters, with return value

NSString *text = ^ () {

return @ "has a return value, no parameters";

}();

NSLog (@ "%@", text);

4---with parameters, return value

}

5. Global block Variables

First, define a global block

{

Int (^myblock) (int a, int b);

}

#pragma mark-Global block variable

-(void) createmyblock{

Defining a block variable

Int (^sumblock) (int x,int y);

Implement block, and assign values

Sumblock = ^ (int x,int y) {

return x+y;

};

Direct assignment, the block variable can be directly assigned to the value

Myblock = Sumblock;

}

Global block can be directly called, directly assigned value

Global block variable

[Self createmyblock];

NSLog (@ "sum:%d", Myblock (20,60));

Of course, the initial understanding of block should also have block application scenarios, blocks and variables, block memory management Some problems, I will not write??。 Because I am a small rookie ~, so, I have to write homework to do exercises, trouble everyone do not spit groove, much encouragement, thank you. Hope to and I just started learning iOS classmates have a little help, summed up is not very good, if there are errors, please correct me, I will humbly learn from you.

The first knowledge of block