block块的用法

block块有3种用法：1.block作为对象的属性，2.block作为方法的参数，3.block作为返回值!!!(扩展非常强!!)。
我们现在先来看看第一种用法：block作为对象的属性，好处是把block传给了person类，person对象回调了block块。
Person.h

@interface Person : NSObject

/** block :ARC使用strong  非ARC copy  */
@property(nonatomic, strong) void(^block)();

@end

ViewController.m

#import "ViewController.h"
#import "Person.h"

@interface ViewController ()
@property(strong, nonatomic)Person *p;
@end

@implementation ViewController

- (void)viewDidLoad {
    [super viewDidLoad];

    //1.block作为对象的属性
    Person *p = [[Person alloc] init];

    //block -- inlineBlock
    void(^ZBBlock)() = ^() {
        NSLog(@"block");
    };

    p.block = ZBBlock;
    _p = p;
}

- (void)touchesBegan:(NSSet<UITouch *> *)touches withEvent:(UIEvent *)event{
    self.p.block();
}

第二种：block作为方法的参数，用处是ViewController回调了block代码块,Person对象可以往ViewCrotroller传值和传事件，类似代理。
Person.h

@interface Person : NSObject

- (void)eat:(void(^)(NSString *))block;

@end

ViewController.m
#import "ViewController.h"
#import "Person.h"

@interface ViewController ()

@end

@implementation ViewController

- (void)viewDidLoad {
    [super viewDidLoad];
    // Do any additional setup after loading the view, typically from a nib.

    //2.block作为方法的参数
    Person *p = [[Person alloc] init];
    [p eat:^(NSString *s) {
        NSLog(@"爱吃%@", s);
    }];

}

第三种：block作为返回值。因为函数有返回值，所以可以用.语法调用方法。返回值是block。
Person.h

@interface Person : NSObject

- (void(^)(int))run;

@end
    Person.m
#import "Person.h"

@implementation Person

- (void (^)(int))run{
    return ^(int m){
        NSLog(@"哥们跑了%d米", m);
    };
}

@end
    ViewController.m
#import "ViewController.h"
#import "Person.h"

@interface ViewController ()

@end

@implementation ViewController

- (void)viewDidLoad {
    [super viewDidLoad];

    //3.block作为返回值
    Person *p = [[Person alloc] init];
    p.run(300);

}