控制器之间的数据传递——全局变量传值

全局变量传值

一. 实现步骤

1. 在界面2中声明一个全局变量，并且用它保存需要传递的值

2. 在界面1中用extern声明界面2中的全局变量，就可使用他所保存的值赋值

二. extern优缺点

1. 优点

   a.全局可视，任何一个函数都可以访问和更改变量值
   b.内存地址固定，读写效率高

2. 缺点

   a.容易造成命名冲突
   b.当值不正确或者出错时，很难确定是哪个函数更改过这个变量
   c.不支持多线程

三. 具体实现

1. AppDelegate类

---------- AppDelegate.m文件

#import "AppDelegate.h"
#include "OneViewController.h"

@interface AppDelegate ()

@end

@implementation AppDelegate

- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions {

// 1. 创建窗口
self.window = [[UIWindow alloc] initWithFrame:[UIScreen mainScreen].bounds];

// 2. 创建窗口的根控制器
// 2.1 创建导航控制器的根控制器
UIViewController *oneVc = [[OneViewController alloc] init];
// 2.2 创建导航控制器
UINavigationController *nav = [[UINavigationController alloc] initWithRootViewController:oneVc];
// 2.3 给窗口设置根控制器
self.window.rootViewController = nav;

// 3. 设置窗口为主窗口并显示窗口
  [self.window makeKeyAndVisible];

// 隐藏导航控制器的导航条
  nav.navigationBarHidden = YES;

return YES;
}

@end

2. OneViewController类

---------- OneViewController.m文件

#import "OneViewController.h"
#import "TwoViewController.h"

// 必须要用extern关键字修饰，才能使用
extern NSString *PassData;

@interface OneViewController ()

@property (nonatomic,strong) UITextField *textField;

@end

@implementation OneViewController

- (void)viewDidLoad {
  [super viewDidLoad];

//设置控制器View的背景颜色
self.view.backgroundColor = [UIColor greenColor];

// 创建点击按钮
UIButton *clickBtn = [UIButton buttonWithType:UIButtonTypeCustom];
  clickBtn.frame = CGRectMake(10, 100, 80, 40);
  clickBtn.backgroundColor = [UIColor whiteColor];
  [clickBtn setTitle:@"到界面2" forState:UIControlStateNormal];
  [clickBtn setTitleColor:[UIColor blackColor] forState:UIControlStateNormal];
  [clickBtn setTitleColor:[UIColor redColor] forState:UIControlStateHighlighted];
  [clickBtn addTarget:self action:@selector(btnClick) forControlEvents:UIControlEventTouchUpInside];
  [self.view addSubview:clickBtn];

// 创建文本框
  _textField = [[UITextField alloc] initWithFrame:CGRectMake(10, 150, 250, 40)];
  _textField.borderStyle = UITextBorderStyleRoundedRect;
  _textField.backgroundColor = [UIColor whiteColor];
  [self.view addSubview:_textField];

}

#pragma mark - 点击事件

- (void)btnClick {

// 创建界面2，并压入栈
  TwoViewController *twoVc = [[TwoViewController alloc] init];
  [self.navigationController pushViewController:twoVc animated:YES];

}

- (void)viewWillAppear:(BOOL)animated {

  _textField.text = PassData;

}

@end

3. TwoViewController类

---------- TwoViewController.m文件

#import "TwoViewController.h"

// 设置全局变量，用于在不同的文件中传值
NSString *PassData;

@interface TwoViewController ()

@property (nonatomic,strong) UITextField *textField;

@end

@implementation TwoViewController

- (void)viewDidLoad {
    [super viewDidLoad];

//设置控制器View的背景颜色
self.view.backgroundColor = [UIColor yellowColor];

// 创建点击按钮
UIButton *clickBtn = [UIButton buttonWithType:UIButtonTypeCustom];
  clickBtn.frame = CGRectMake(10, 100, 80, 40);
  clickBtn.backgroundColor = [UIColor whiteColor];
  [clickBtn setTitle:@"传 值" forState:UIControlStateNormal];
  [clickBtn setTitleColor:[UIColor blackColor] forState:UIControlStateNormal];
  [clickBtn setTitleColor:[UIColor redColor] forState:UIControlStateHighlighted];
  [clickBtn addTarget:self action:@selector(btnClick) forControlEvents:UIControlEventTouchUpInside];
  [self.view addSubview:clickBtn];

// 创建文本框
  _textField = [[UITextField alloc] initWithFrame:CGRectMake(10, 150, 250, 40)];
  _textField.borderStyle = UITextBorderStyleRoundedRect;
  _textField.backgroundColor = [UIColor whiteColor];
  [self.view addSubview:_textField];
}

#pragma mark - 点击事件

- (void)btnClick {

  PassData = _textField.text;

// 跳转界面
  [self.navigationController popViewControllerAnimated:YES];

}

@end