傻瓜学编程之block_1

Posted 2020-10-10 肖无情

1、引出

1.1、int pp = 3;for循环为dd赋值并 调用 finprint(int ,int)函数 获取pp*dd的乘积，输出

void finalValue(int d, int scale){
    
    printf(".......%d",scale*d);
    printf("\\n");
    
}

void finprint(int j,int  i){
    
    printf("其他操作\\n");

    void (*fin)(int d,int s) = &finalValue;
    
    fin(j,i);  
}

- (void)viewDidLoad {
    [super viewDidLoad];
    int dd ;
    int pp = 3;
    for (int j= 0; j<5; j++) {
        dd=j;
        finprint(pp,dd);
    }
}

 a：必须获取finalValue函数的名字，

 b: finalValue如果想使用 dd,pp （也即finprint中的形式参数 j和i） 必须传递到finalValue中才可以使用；

 

 1.2、不用必须获取finalValue函数的名字，

void finprint(int j,int  i){
    
    printf("其他操作\\n");

    void (^fina)(int d,int s) = ^(int d,int s){
        printf(".......%d",s*d);
        printf("\\n");
    };
    fina(j,i);
}

- (void)viewDidLoad {
    [super viewDidLoad];
    int dd ;
    int pp = 3;
    for (int j= 0; j<5; j++) {
        dd=j;
        finprint(pp,dd);
    }
}

 

1.3、不用传递参数参数也可以访问finprint中的形式参数 j和i；

void finprint(int j,int  i){
    
    printf("其他操作\\n");

    void (^fina)(void) = ^(void){
        printf(".......%d",j*i);
        printf("\\n");
    };
    fina();
}

 2、 block

2.1、简单概述：带有自动变量（局部变量）的匿名函数；

        1）没有函数名

        2） 带有”^“号

2.2、语法格式：具体格式

  ^ 返回值类型 参数列表  表达式

 其中  返回值类型 参数列表 可省略

 

block
How Do I Declare A Block in Objective-C?

As a local variable:
returnType (^blockName)(parameterTypes) = ^returnType(parameters) {...};


As a property:
@property (nonatomic, copy, nullability) returnType (^blockName)(parameterTypes);

As a method parameter:
- (void)someMethodThatTakesABlock:(returnType (^nullability)(parameterTypes))blockName;

As an argument to a method call:
[someObject someMethodThatTakesABlock:^returnType (parameters) {...}];

As a typedef:
typedef returnType (^TypeName)(parameterTypes);
TypeName blockName = ^returnType(parameters) {...};

This site is not intended to be an exhaustive list of all possible uses of blocks.If you find yourself needing syntax not listed here, it is likely that a typedef would make your code more readable.Unable to access this site due to the profanity in the URL? http://goshdarnblocksyntax.com is a more work-friendly mirror.