OBJECTIVE-C (13) code blocks---block

• Block type

Block is a data type that is widely used in iOS development and is highly recommended by Apple, which functions like a function pointer in C.

^ is a unique symbol of block.

The implementation code for the block is included in the {}.

In most cases, the inline form is defined and used.

void (^demoblock) () = ^ {NSLog (@ "demo Block");} Int (^sumblock) (int, int) = ^ (int x, int y) {return x + y;}

Block usage is similar to the use of function pointers

Int (^sumblock) (int, int) = ^ (int a, int b) {return a>b?a:b;} int c = Sumblock (10, 20); NSLog (@ "c=%d", c);

External variables can be accessed inside the block

External local variables, block internal cannot be modified, global variables can be.

If the local variable uses the __block declaration, it can be modified internally.

int a = 10;__block int b = 20;void (^myblock) () Myblock = ^ {NSLog (@ "a=%d", a); b = 20;} Myblock ();

In fact, a local variable is copied when the block is defined (copy)

The importance of block: it is very convenient to handle asynchronous tasks, which is also the difficulty of block application

This article is from the "Teacheran" blog, make sure to keep this source http://annmeng.blog.51cto.com/3321237/1745694

OBJECTIVE-C (13) code blocks---block