关于block的传值

#import <UIKit/UIKit.h>

@interface BViewController : UIViewController

@property(nonatomic,strong)void (^ returnStr) (NSString *str);
- (void)returnStr:(void (^) (NSString *str))str;

@end

1.首先要更正自己的一个观点，属性为block函数是能够被strong修饰的（自己不知道怎么搞的，一直以为其职能被assign修饰）

2.那就是关于block的传值了，直接代码

在A控制器中

- (IBAction)tiaoZhuan:(id)sender {

    //A控制器中调用B控制器中带有block函数的方法

    [self.BVC returnStr:^(NSString *str) {

        self.label.text = str;

        [self.view setNeedsDisplay];

    }];

    [self presentViewController:self.BVC animated:YES completion:nil];

}

在B控制器中 .h文件

#import <UIKit/UIKit.h>

@interface BViewController : UIViewController
//这里的block属性需要用strong修饰
@property(nonatomic,strong)void (^ returnStr) (NSString *str);
- (void)returnStr:(void (^) (NSString *str))str;

@end

.m文件

- (void)viewDidLoad {
    [super viewDidLoad];
    NSLog(@"B-viewDidLoad");
    UIButton *button = [[UIButton alloc]initWithFrame:CGRectMake(100, 100, 100, 100)];
    [button setTitle:@"返回" forState:UIControlStateNormal];
    [button addTarget:self action:@selector(back:) forControlEvents:UIControlEventTouchUpInside];
    [self.view addSubview:button];
}

- (void)returnStr:(void (^) (NSString *str))str {
    self.returnStr = str;
    //str(@"我是反回来的");
}

//返回函数
- (void)back:(UIButton *)sender {
    self.returnStr(@"我是反回来的");
    [self dismissViewControllerAnimated:YES completion:nil];
}