Day15 oc block data type

define block variable

int (^myBlock)(int ,int );

 

normal code block

{
     do something... member variables in a code block are scoped to the end of the code block
}

 

block encapsulates a block of code

A block encapsulates a piece of code that can be called at any time. Much like functions, you can save code and have parameters and return values.

^(){
};

^{
};

^(int a ,int b){
};

 

The definition + encapsulation is as follows, the sign of the block: ^

void (^blockName)()=^{//If the block has no formal parameters, you can omit ^()
do something...
};

 Use block to call block internal code

blockName();

 

block with parameter return value

int (^blockName)(int a,int b)=^(int a ,int b){
do something...

return a+b;
};

int c = blockName(1,2);

Similar to pointer functions in C

int sum(int a ,int b)
{
    return a+b;
}

int (*p)(int, int) = sum();
int c = p(1+2);

  

block member variable scope

int a = 1;
__block int b = 2;
void (^blockName)();
blockName = ^{
    //1, inside the block can access external variables
    //2. By default, block cannot modify external local variables such as a= 2;
    //3. If you want to modify external variables, you need to add __block (two underscores) such as b = 1;
};
blockName();

 typedef definition block

//typedef defines function pointer
typedef int (*P)(int, int);

int sum(int a ,int b)
{
    return a+b;
}

P p1 = sum
P p2 = sum;

 in the same block

typedef (^BlockName)(int, int);//Define the type, you can use the BlockName type to define block variables in the future

BlockName sumBlock;
sumBlock = ^(int a ,int b){
    return a + b;
};

BlockName minusBlock = ^(int a ,int b){
    return a - b;
};