block对变量的捕获

1：可以捕获不可以修改变量

局部变量

2：可以捕获且可以修改变量

全局变量
静态变量
__block修饰的局部变量

下面我们看个例子，大家根据例子输出结果来思考加深理解。
.h

#import <UIKit/UIKit.h>

@interface Person : NSObject

@property (nonatomic, copy) NSString *name;

@end


typedef void(^PersonBlock)(Person *);

@interface ViewController : UIViewController

@property (nonatomic, copy) PersonBlock myBlcok;

@end

.m

#import "ViewController.h"

@implementation Person

@end

@interface ViewController ()

@end

@implementation ViewController

- (void)viewDidLoad {
    [super viewDidLoad];
    
    [self testBlock];
}


-(void)testBlock{
    Person *p1 = [[Person alloc]init];
    p1.name = @"p1";
    
    Person *p2 = [[Person alloc]init];
    p2.name = @"p2";
    
    Person *p3 = [[Person alloc]init];
    p3.name = @"p3";
    
    NSArray *arr = @[p1,p2,p3];
    
    for (Person *p in arr) {
        
        int i=2;
        dispatch_async(dispatch_get_main_queue(), ^{
            NSLog(@"没传参数时%@",p.name);
            NSLog(@"%d",i);
        });
        i=4;
        
        _myBlcok = ^(Person *p){
            NSLog(@"传递参数时%@",p.name);
        };
        _myBlcok(p);
        
        p.name = @"p-new";
    }
    
    
    void (^Block)(int) = ^(int i){
        NSLog(@"值是%d",i*2);
    };
    int a = 4;
    Block(a);
    dispatch_async(dispatch_get_main_queue(), ^{
        NSLog(@"主线程调用最后值是%d",a*2);
    });
    a = 6;
    
    
}


@end

结果：

2019-04-11 15:51:11.475200+0800 Block[63860:3183459] 传递参数时p1
2019-04-11 15:51:11.475373+0800 Block[63860:3183459] 传递参数时p2
2019-04-11 15:51:11.475499+0800 Block[63860:3183459] 传递参数时p3
2019-04-11 15:51:11.475609+0800 Block[63860:3183459] 值是8
2019-04-11 15:51:11.481302+0800 Block[63860:3183459] 没传参数时p-new
2019-04-11 15:51:11.481674+0800 Block[63860:3183459] 2
2019-04-11 15:51:11.481816+0800 Block[63860:3183459] 没传参数时p-new
2019-04-11 15:51:11.481919+0800 Block[63860:3183459] 2
2019-04-11 15:51:11.482052+0800 Block[63860:3183459] 没传参数时p-new
2019-04-11 15:51:11.482152+0800 Block[63860:3183459] 2
2019-04-11 15:51:11.482262+0800 Block[63860:3183459] 主线程调用最后值是8