IOS外部变量(Extern)的用法

来源：互联网发布：淘宝联盟需要交钱吗编辑：程序博客网时间：2024/06/04 20:02

在这里做了一个Demo,ViewController声明外部变量并使用,ExternViewController负责修改外部变量的值

ViewController.m

#import "ViewController.h"#import "ExternViewController.h"NSString *externString = @"234";@interface ViewController ()@end@implementation ViewController//在这里声明外部变量也可以- (void)viewDidLoad{    [super viewDidLoad];    UIButton *button = [UIButton buttonWithType:UIButtonTypeCustom];    [button setFrame:CGRectMake(0, 0, 320, 50)];    [button setTitle:@"To ExternViewController" forState:UIControlStateNormal];    [button setBackgroundColor:[UIColor orangeColor]];    [button addTarget:self action:@selector(buttonAct) forControlEvents:UIControlEventTouchUpInside];    [self.view addSubview:button];}- (void)buttonAct{    ExternViewController *view = [[ExternViewController alloc]init];    [self presentViewController:view animated:YES completion:^{            }];}- (void)viewWillAppear:(BOOL)animated{    [super viewWillAppear:animated];    NSLog(@"ViewController externString:%@",externString);}@end

ExternViewController.m

#import "ExternViewController.h"extern NSString *externString;@interface ExternViewController ()@end@implementation ExternViewController- (void)viewDidLoad{    [super viewDidLoad];// Do any additional setup after loading the view.        self.view.backgroundColor = [UIColor whiteColor];        NSLog(@"get externString value:%@",externString);        externString = [NSString stringWithFormat:@"%i",arc4random_uniform(1000)];        NSLog(@"ExternViewController exchange externString value:%@",externString);        UIButton *button = [UIButton buttonWithType:UIButtonTypeCustom];    [button setFrame:CGRectMake(0, 0, 320, 50)];    [button setTitle:@"Back" forState:UIControlStateNormal];    [button setBackgroundColor:[UIColor redColor]];    [button addTarget:self action:@selector(buttonAct) forControlEvents:UIControlEventTouchUpInside];    [self.view addSubview:button];}- (void)buttonAct{    [self dismissViewControllerAnimated:YES completion:^{            }];}@end

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