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/3321237/1745634
OBJECTIVE-C (13) code blocks---block