一、简述

　　在iOS开发过程中，页面跳转时在页面之间进行数据传递是很常见的事情，我们称这个过程为页面传值。页面跳转过程中，从主页面跳转到子页面的数据传递称之为正向传值；反之，从子页面返回主页面时的数据传递称之为反向传值。

　　目前我所了解和掌握的传值方式有：

1. 属性传值
2. 单例传值
3. NSUserDefaults传值
4. 代理传值
5. block传值
6. 通知传值
7. KVO/KVC  iOS----KVC和KVO 详解

二、页面传值的详解

2.0 准备工作

　　为了实现页面之间传值，我们需要准备两个页面，代码结构如下图所示。其中，KLMainViewController为主主页面，KLSubViewController为子页面，页面之间的跳转使用UINavigationController来实现。每个页面中都有一个文本编辑框，我们需要将其中一个页面文本框中的内容传递到另一个页面中。

　　　　 　　　　

#import "KLMainViewController.h"
#import "KLSubViewController.h"

@interface KLMainViewController ()

@property (strong, nonatomic) UITextField *textField;
@property (strong, nonatomic) UIButton *button;

@end

@implementation KLMainViewController

- (void)viewDidLoad {
    [super viewDidLoad];
    self.title = @"主界面";
    
    _textField = [[UITextField alloc] init];
    _textField.textColor = [UIColor redColor];
    _textField.textAlignment = NSTextAlignmentCenter;
    _textField.backgroundColor = kBgColor;
    _textField.text = @"主界面的label信息";
    [self.view addSubview:_textField];
    WEAKSELF
    [_textField mas_makeConstraints:^(MASConstraintMaker *make) {
        make.center.mas_equalTo(weakSelf.view).mas_offset(0.0f);
        make.left.mas_equalTo(weakSelf.view).mas_offset(15.0f);
        make.right.mas_equalTo(weakSelf.view).mas_offset(-15.0f);
    }];
    
    _button = [UIButton buttonWithType:UIButtonTypeCustom];
    [_button setTitle:@"跳转到子界面" forState:UIControlStateNormal];
    [_button setTitleColor:[UIColor blueColor] forState:UIControlStateNormal];
    [_button addTarget:self action:@selector(btnClicked:) forControlEvents:UIControlEventTouchUpInside];
    [self.view addSubview:_button];
    [_button mas_makeConstraints:^(MASConstraintMaker *make) {
        make.centerX.mas_equalTo(weakSelf.view).mas_offset(0.0f);
        make.top.mas_equalTo(weakSelf.textField.mas_bottom).mas_offset(40.0f);
    }];
    
}

- (void) btnClicked:(UIButton *)btn {
    KLSubViewController *subVC = [[KLSubViewController alloc] init];
    [self.navigationController pushViewController:subVC animated:YES];
}

@end

//KLSubViewController.h
#import <UIKit/UIKit.h>

NS_ASSUME_NONNULL_BEGIN

@interface KLSubViewController : UIViewController

@property (strong, nonatomic) UITextField *textField;
@property (strong, nonatomic) UIButton *button;

@property (strong, nonatomic) NSString *content;

@end

NS_ASSUME_NONNULL_END

//KLSubViewController.m
#import "KLSubViewController.h"

@interface KLSubViewController ()

@end

@implementation KLSubViewController

- (void)viewDidLoad {
    [super viewDidLoad];
    self.view.backgroundColor = [UIColor whiteColor];
    self.title = @"子界面";
    
    _textField = [[UITextField alloc] init];
    _textField.textColor = [UIColor redColor];
    _textField.textAlignment = NSTextAlignmentCenter;
    _textField.backgroundColor = kBgColor;
    _textField.text = @"子界面的label信息";
    [self.view addSubview:_textField];
    WEAKSELF
    [_textField mas_makeConstraints:^(MASCons