IOS learning-9, ios-9

IOS learning-9, ios-9

A video from Jay Chou.

Block is used to save a piece of code.

Block flag: ^

Blocks are similar to functions.:

1 ).Code can be saved2 ).Return Value3 ).Parameter

Temp1: Block without return values or parameters

If the block does not have a form parameter, You can omit ()

Void (^ myblock) () = ^ {NSLog (@ "----------"); NSLog (@"----------");}; // call the internal code myblock () of the block using the block variable ();

Temp2: Return Value and Parameter

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

Temp3: Use a block to output n horizontal lines.

Void (^ lineblock) (int) = ^ (int n) {for (int I = 1; I <n; I ++) {NSLog (@ "-------") ;}; // No return value. Add the lineblock (5) parameter of the int type );

Temp 4:

_ Block int a = 10; void (^ block) (); block = ^ {/* block can access external variables by default, you cannot add the _ block keyword to the local variable within the block. You can modify this local variable within the block */a = 20; NSLog (@ "% d ", a) ;}; block ();

Temp 5: Use typedef to define the block type

// Type + variable MyBlock sumBlock; sumBlock = ^ (int a, int B) {return a + B ;}; sumBlock (10, 9); // subtract MyBlock minusBlock; minusBlock = ^ (int a, int B) {return a-B ;}; minusBlock (10, 9); // multiply MyBlock multipBlock; multipBlock = ^ (int a, int B) {return a * B;}; multipBlock (); // division MyBlock divideBlock; divideBlock = ^ (int a, int B) {return a/B ;}; divideBlock (); NSLog (@ "\ n % d", sumBlock (), minusBlock ), multipBlock (10, 9), divideBlock (10, 2 ));

Summary:

1. How to define block Variables

int (^sumBlock)(int,int);void (^myBlock)();

2. How to Use block to encapsulate code

^ (Int a, int B) {return a-B ;}; // No parameter ^ () {NSLog (@"-----");} // No return value ^ {NSLog (@"-----");}

3. block access to external variables

1. The block can access external variables. 2. By default, the block cannot modify external local variables.
3. Add the _ block keyword to the local variable. This local variable can be modified within the block.

4. Use typedef to define the block type

Typedef int (^ MyBlock) (int, int); // you can use MyBlock to define the block Variable MyBlock block; MyBlock b1, b2; b1 = ^ (int, int B) {return a + B ;}; MyBlock b3 = ^ (int a, int B) {return a + B ;};