IOS开发-NSUserDefaults的基本使用，缓存数据实现数据持久化

NSUserDefaults是iOS与 macOS 中的一个存储对象。它用于存储应用程序运行期间和退出后需要保存的数据。

NSUserDefaults的特点:- 基于键值对:使用字符串作为键名存储数据。
- 支持的类型:NSString、NSNumber、NSDate、NSArray、NSDictionary等基本数据结构。
- 存储在本地:数据存储在本地文件中,不会因为应用程序退出而丢失。
- 可以监听变化:可以注册通知监听 NSUserDefaults 对象变化。通过 NSUserDefaults ,我们可以存储:- 应用设置:比如亮度、声音等用户偏好设置
- 配置信息:分辨率、访问权限、主题等配置
- 用户信息:用户名、头像、地区等
- 状态信息:在应用程序重新启动后仍然有效。

使用步骤:

1. 获取默认的用户defaults对象:

NSUserDefaults *defaults = [NSUserDefaults standardUserDefaults];

2. 写入要存储的数据:

 [defaults setObject:@"用户1" forKey:@"username"];

可以写入的值有：NSString、NSNumber、NSDate、NSArray、NSDictionary。

3. 读取缓存的数据:

   NSString *username = [defaults stringForKey:@"username"];

4. 注册defaults变化通知:

[[NSNotificationCenter defaultCenter] addObserver:self
                                            selector:@selector(defaultsDidChange:)
                                                name:NSUserDefaultsDidChangeNotification
                                              object:nil];

5. 监听通知:

- (void)defaultsDidChange:(NSNotification *)notification {
    // 注册的defaults值发生变化,会触发这个方法
        NSLog(@"修改了%@",[notification.object stringForKey:@"username"]);
}

6. 移除通知监听:

[[NSNotificationCenter defaultCenter] removeObserver:self];

完整代码：

AppDelegate.m

//
//  AppDelegate.m
//  viewtest
//
//  Created by 001 on 2023/5/9.
//
#define WYColor(r, g, b) [UIColor colorWithRed:(r)/255.0 green:(g)/255.0 blue:(b)/255.0 alpha:1.0]
#import "AppDelegate.h"
#import "labelpage.h"
#import "imgpage.h"

@interface AppDelegate ()

@end

@implementation AppDelegate
- (void)defaultsDidChange:(NSNotification *)notification {
    // 注册的defaults值发生变化,会触发这个方法
        NSLog(@"修改了%@",[notification.object stringForKey:@"username"]);
}
- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions {
    NSUserDefaults *defaults = [NSUserDefaults standardUserDefaults];
    [defaults setObject:@"用户1" forKey:@"username"];
    [[NSNotificationCenter defaultCenter] addObserver:self
                                            selector:@selector(defaultsDidChange:)
                                                name:NSUserDefaultsDidChangeNotification
                                              object:nil];
    labelpage *labelpageview = [[labelpage alloc] init];
    imgpage *imgpageview = [[imgpage alloc] init];
    self.window.rootViewController = imgpageview;
    [self.window makeKeyAndVisible];
    NSLog(@"执行了");
    return YES;
}

#pragma mark - UISceneSession lifecycle


@end

imgpage.m

//
//  imgpage.m
//  blog
//
//  Created by 001 on 2023/7/2.
//

#import "imgpage.h"
#import <AVFoundation/AVFoundation.h>
@interface imgpage ()

@end

@implementation imgpage

- (void)viewDidLoad {
    UIImageView *imgview = [[UIImageView alloc] init];
    imgview.frame =CGRectMake((self.view.frame.size.width-100)/2, (self.view.frame.size.height-100)/2, 100, 100);
    NSURL *url = [NSURL URLWithString:@"https://img0.baidu.com/it/u=1752903520,1572100722&fm=253&fmt=auto&app=138&f=JPEG?w=521&h=500"];
    NSData *data = [NSData dataWithContentsOfURL:url];
    UIImage *image = [UIImage imageWithData:data];
    imgview.image = image;
//    imgview.image = [UIImage imageNamed:@"icon"];
//    //设置圆角
//    imgview.layer.cornerRadius = imgview.frame.size.width / 2;
//    //将多余的部分切掉
//    imgview.layer.masksToBounds = YES;
//    //开始对imageView进行画图
//     UIGraphicsBeginImageContextWithOptions(imgview.bounds.size, NO, 1.0);
//     //使用贝塞尔曲线画出一个圆形图
//     [[UIBezierPath bezierPathWithRoundedRect:imgview.bounds cornerRadius:imgview.frame.size.width] addClip];
//     [imgview drawRect:imgview.bounds];
//      imgview.image = UIGraphicsGetImageFromCurrentImageContext();
//      //结束画图
//     UIGraphicsEndImageContext();
     
     UIBezierPath *maskPath = [UIBezierPath bezierPathWithRoundedRect:imgview.bounds byRoundingCorners:UIRectCornerAllCorners cornerRadii:imgview.bounds.size];

        CAShapeLayer *maskLayer = [[CAShapeLayer alloc]init];
        //设置大小
        maskLayer.frame = imgview.bounds;
        //设置图形样子
        maskLayer.path = maskPath.CGPath;
        imgview.layer.mask = maskLayer;
    
    self.view.backgroundColor = [UIColor whiteColor];
    [self.view addSubview:imgview];
    NSUserDefaults *defaults = [NSUserDefaults standardUserDefaults];
    [defaults setObject:@"234" forKey:@"username"];
    NSString *username = [defaults stringForKey:@"username"];
    NSLog(@"用户名称%@",username);
    [super viewDidLoad];
    // Do any additional setup after loading the view.
}

/*
#pragma mark - Navigation

// In a storyboard-based application, you will often want to do a little preparation before navigation
- (void)prepareForSegue:(UIStoryboardSegue *)segue sender:(id)sender {
    // Get the new view controller using [segue destinationViewController].
    // Pass the selected object to the new view controller.
}
*/

@end

效果图：