24th-day notes for IOS (Block Introduction) and 24th-day ios

24th-day notes for IOS (Block Introduction) and 24th-day ios

Knowledge points of IOS Learning (oc language)

I. Introduction of Block

1) concept: block is a data type. It is similar to a function without a name in C language. It can receive parameters or return values that are called like C functions.

Encapsulate a piece of code that can call a block anywhere or as a function parameter, and return a function value.

2) Block instance code

1 // defines a block type MyBlock. A variable of the MyBlock type can only point to the parameter with two int types and the code block that returns the int type 2 typedef int (^ MyBlock) (int, int ); 3 // define a function pointer 4 int (* pMath) (int, int); 5 6 int add (int a, int B) 7 {8 return a + B; 9} 10 11 int sub (int a, int B) 12 {13 return a-B; 14} 15 16 int main (int argc, const char * argv []) {17 @ autoreleasepool {18 pMath = add; // point to function pointer 19 // NSLog (@ "sum: % d", pMath (2, 3); 20 pMath = sub; 21 22 // defines a block. Can point to a parameter with two int values, return the int code block 23 // start with ^ as the code block, followed by () as the parameter, and then {} code block 24 int (^ bloke1) (int, int) = ^ (int a, int B) {25 return a + B; 26}; 27 28 int s = bloke1 (3,5 ); 29 NSLog (@ "s: % d", s); 30 // define a block to point to a code block without a parameter and no return value (No parameter, void can be omitted) 31 void (^ block2) (void) = ^ {32 NSLog (@ "programing is fun! "); 33}; 34 block2 (); 35 int (^ block3) (int, int) = ^ (int a, int B) {36 return a-B; 37 38}; 39 40 // defines a variable of the MyBlock type, and assigns a value to the Code Block 41 MyBlock block4 = ^ (int a, int B) {42 return a * B; 43 }; 44 45 NSLog (@ "% d", block4 (2, 5); 46 47 int c = 10; 48 _ block int d = 1; 49 // The block can access the variable outside the block but cannot be modified. If you need to modify the variable, add _ block to it to modify 50 void (^ block5) (void) =={ 51 d = d + 2; 52 NSLog (@ "c: % d, d: % d", c, d); 53}; 54 block5 (); 55} 56 return 0; 57}