iOS Block逆向传值

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逆向传值的方法有很多如代理、通知、block、KVC等等。但是相对来说block是最简单方便的，前提是处理好使用block的细节问题，如循环引用这常见的问题。

一.注意点

• 传值方定义block，接收方只需告诉传值方我们需要你传值了。
• 传值方定义block，接收方实现block。
• 在需要传值的时候调用block。
• 接收方在需要用到传值的地方告诉传值方，你可以传值了，接收值并处理逻辑。

二.实现效果

逆向传值

三.实现步骤

1.接收方

#define HPWidth self.view.frame.size.width
#define HPHeight self.view.frame.size.height

#import "ViewController.h"
#import "HPReverseViewController.h"

@interface ViewController ()
@property (nonatomic ,strong) UILabel *label;

@property (nonatomic ,strong) UIButton *btn;

@end

@implementation ViewController

- (void)viewDidLoad {
    [super viewDidLoad];

    self.title = @"block逆向传值";
    self.view.backgroundColor = [UIColor whiteColor];

    [self btn];
    [self label];
    
    
}
- (void)buttonClick{
    HPReverseViewController *reverseVc = [[HPReverseViewController alloc]init];
    __weak typeof(self) weakSelf = self;
    reverseVc.reverseValueBlock = ^(NSString *HPReverseValue) {
        weakSelf.label.text = HPReverseValue;
    };
    [self.navigationController pushViewController:reverseVc animated:YES];
}
- (UIButton *)btn{
    if (!_btn) {
        _btn = [UIButton buttonWithType:UIButtonTypeCustom];
        _btn.frame = CGRectMake(HPWidth/2-40,150,80, 50);
        _btn.titleLabel.font = [UIFont systemFontOfSize:18];
        [_btn setTitle:@"下一步" forState:UIControlStateNormal];
        [_btn setTitleColor:[UIColor greenColor] forState:UIControlStateNormal];
        [_btn addTarget:self action:@selector(buttonClick) forControlEvents:UIControlEventTouchUpInside];
        [self.view addSubview:_btn];
    }
    return _btn;
}
- (UILabel *)label{
    if (!_label) {
        _label = [[UILabel alloc]init];
        _label.frame = CGRectMake(HPWidth/2-50, 300, 100, 50);
        _label.backgroundColor = [UIColor greenColor];
        _label.textAlignment = NSTextAlignmentCenter;
        _label.font = [UIFont systemFontOfSize:18];
        _label.text = @"逆向传值";
        [self.view addSubview:_label];
    }
    return _label;
}



@end

2.传值方

.h文件
#import <UIKit/UIKit.h>

/**
 定义一个block类型
 
 @param HPReverseValue 逆向传值
 */
typedef void (^HPReverseValueBlock) (NSString *HPReverseValue);


@interface HPReverseViewController : UIViewController

/**
 声明block属性 在接收方实现.
 */
@property (nonatomic ,copy) HPReverseValueBlock reverseValueBlock;

@property (weak, nonatomic) IBOutlet UIButton *backBtn;
@property (weak, nonatomic) IBOutlet UITextField *valueTextFile;

@end
-------------------------------------------------------------------------------

.m文件

#import "HPReverseViewController.h"

@interface HPReverseViewController ()

@end

@implementation HPReverseViewController

- (void)viewDidLoad {
    [super viewDidLoad];
    self.title = @"传值方";
}
- (IBAction)btnClick:(id)sender {
    __weak typeof(self) weakSelf = self;
    if (self.reverseValueBlock) {
        //将值传到接收方
        weakSelf.reverseValueBlock(weakSelf.valueTextFile.text);
    }
    
    [self.navigationController popViewControllerAnimated:YES];
    
    
}



@end