block 传值

使用block传值一般都是后面控制器往前面控制器传值时使用
前页面

#import "ViewController.h"

#import "SecondController.h" // 后面页面
@interface ViewController ()

@property (nonatomic, strong)UILabel *labels;
@property (nonatomic, strong)UIButton *buttons;
@end

@implementation ViewController

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

- (void)addViews {

    self.labels = [[UILabel alloc]init];
    self.labels.backgroundColor = [UIColor redColor];
    self.labels.frame = CGRectMake(100, 100, 200, 40);

    [self.view addSubview:self.labels];

    self.buttons = [UIButton buttonWithType:UIButtonTypeCustom];
    self.buttons.frame = CGRectMake(100, 200, 50, 30);
    self.buttons.backgroundColor = [UIColor blackColor];
    [self.buttons addTarget:self action:@selector(actionss) forControlEvents:UIControlEventTouchUpInside];
    [self.view addSubview:self.buttons];

}


- (void)actionss
{
    // 跳转到后面页面 当返回时会携带参数过来
    SecondController *second = [[SecondController alloc]init];
    // block 传值
    [second returnText:^(NSString *showText) {
        self.labels.text = showText;
    }];

    [self presentViewController:second animated:YES completion:nil];
}

@end
*后面页面(和面页面会往前页面传值)*

*.h页面代码*

typedef void(^ReturnTextBlock)(NSString *showText);
@interface SecondController : UIViewController

@property (nonatomic, copy)ReturnTextBlock returnTextBlock;

- (void)returnText:(ReturnTextBlock)block;

*.m页面代码*

#import "SecondController.h"
@interface SecondController ()
@property (nonatomic, strong)UIButton *backB;
@property (nonatomic, strong)UITextField *textFields;
@end

@implementation SecondController

- (void)viewDidLoad {
    [super viewDidLoad];
    self.view.backgroundColor = [UIColor whiteColor];

    [self addBlock];
}

- (void)addBlock {
    self.backB = [UIButton buttonWithType:UIButtonTypeCustom];
    self.backB.backgroundColor = [UIColor purpleColor];
    self.backB.frame = CGRectMake(100, 100, 50, 30);
    [self.backB addTarget:self action:@selector(actionss) forControlEvents:UIControlEventTouchUpInside];
    [self.view addSubview:self.backB];

    self.textFields = [[UITextField alloc]init];
    self.textFields.backgroundColor = [UIColor grayColor];
    self.textFields.frame = CGRectMake(30, 30, (self.view.frame.size.width - 30) / 2, 30);
    [self.view addSubview:self.textFields];
}

- (void)actionss
{
    [self dismissViewControllerAnimated:YES completion:nil];
    NSLog(@"SecondController--- %@", self.textFields.text);
}


- (void)returnText:(ReturnTextBlock)block
{
    self.returnTextBlock = block;
}

- (void)viewWillDisappear:(BOOL)animated
{
    if (self.returnTextBlock != nil) {
        self.returnTextBlock(self.textFields.text);
    }
}
@end

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