iOS基础：NSUserDefault

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一、NSUserDefault介绍

iOS下可以使用NSUserDefault、NSKeyedArchiver、sqlite、CoreData几种常用的方式来存储数据，其中NSUserDefaults用来存储类似用户的配置等这些的数据，后两者用户存储大批量和比较复杂的数据。

NSUserDefault 基本上支持所有的原生数据类型NSString、 NSNumber、NSDate、 NSArray、NSDictionary、BOOL、NSInteger、NSFloat等等。如果要存放自定义的对象（如自定义的类对象），则必须将其转换成NSData存储。

二、NSUserDefault存储和获取数据

//存储数据 NSUserDefaults * user = [NSUserDefaults standardUserDefaults];[user setObject:currentVersion forKey:CZVersionKey];//需要注意的是，NSUserDefaults是定时把缓存中的数据写入磁盘的，而不是即时写入，为了防止在写完NSUserDefaults后程序退出导致的数据丢失，可以在写入数据后使用synchronize强制立即将数据写入磁盘：//运行下面的语句后，NSUserDefaults中的数据即被写入到.plist文件中，如果是在模拟器上运行程序，可以在Mac的/Users/YOUR-USERNAME/Library/Application Support/iPhone Simulator/4.1/Applications/YOUR-APP-DIR/Library/Prefereces目录下面找到一个文件名为YOUR-Bundle_Identifier.plist的plist文件，用Xcode打开该文件，可以看到刚才写入的数据。[user synchronize];//删除数据NSUserDefaults * user = [NSUserDefaults standardUserDefaults];[user  removeObjectForKey:CZVersionKey];//获取数据NSUserDefaults * user = [NSUserDefaults standardUserDefaults];NSString * lastVersion = [user objectForKey:CZVersionKey];

三、转NSData进行存储

//UIImage 实例不能进行存储-(void)imageUserDefault{    UIImage * image = [UIImage imageNamed:@"1"];#if 0    //报错 - [User Defaults] Attempt to set a non-property-list object <UIImage: 0x60800008ece0>, {0, 0} as an NSUserDefaults/CFPreferences value for key image    [self setObject:image withKey:@"image"];#else    //UIImage 实例需要转换为NSData进行存储    NSData *data = nil;    if (UIImagePNGRepresentation(image) == nil) {        data = UIImageJPEGRepresentation(image, 1);    } else {        data = UIImagePNGRepresentation(image);    }    [self setObject:data withKey:@"image"];    NSData * getImageData = [self getObjectWithKey:@"image"];    NSLog(@"getImageData = %@",getImageData);    UIImage * getImage = [UIImage imageWithData:getImageData];    NSLog(@"getImage = %@",getImage);#endif    }

//自定义对象 不能进行存储-(void)customClassUserDefault{    MYView * myView = [[MYView alloc] initWithFrame:self.view.bounds];#if 0    //报错 - Attempt to set a non-property-list object <MYView: 0x7f8b1060b810; frame = (0 0; 375 667); layer = <CALayer: 0x608000034a60>> as an NSUserDefaults/CFPreferences value for key myView    //要想对自定义对象进行存储需要将自定义对象进行归档    [self setObject:myView withKey:@"myView"];#else    NSData * myData = [NSKeyedArchiver archivedDataWithRootObject:myView];    [self setObject:myData withKey:@"myData"];    NSData * getMyData = [self getObjectWithKey:@"myData"];    NSLog(@"getMyData = %@",getMyData);    MYView * getMyView = [NSKeyedUnarchiver unarchiveObjectWithData:getMyData];    NSLog(@"getMyView = %@",getMyView);    //要想MYView实例的属性能存入需要实现coding协议    NSLog(@"getMyView.mySring = %@",getMyView.myString);#endif}

四、利用NSUserDefault判断程序启动

//抽出一个工具类在.h文件中代码如下：#import <Foundation/Foundation.h>@interface FirstLaunchTool : NSObject+(BOOL)isFirstLaunchOfToday;+(BOOL)isFirstLaunch;@end//.m文件中代码如下：+(BOOL)isFirstLaunch{        NSUserDefaults * user = [NSUserDefaults standardUserDefaults];    NSString * firstStr = [user objectForKey:@"firstLaunch"];    if (!firstStr) {        [user setObject:@"firstLaunch" forKey:@"firstLaunch"];        return YES;    }    else{                return NO;    }        }+(BOOL)isFirstLaunchOfToday{        //获取今天的时间    NSDate * date = [NSDate date];    NSDateFormatter * formatter = [[ NSDateFormatter alloc] init];    formatter.dateFormat = @"yyyyMMdd";    NSString * today = [formatter stringFromDate:date];        //与存储时间对比    NSUserDefaults * user =[NSUserDefaults standardUserDefaults];    NSString * yesterday = [user objectForKey:@"today"];    if ([today isEqualToString:yesterday]) {                NSString * countStr = [user objectForKey:@"count"];        NSUInteger count = [countStr integerValue];        count+=1;        [user setObject:[NSString stringWithFormat:@"%lu",count] forKey:@"count"];        [user synchronize];        return NO;    }    else{                [user setObject:today forKey:@"today"];        [user setObject:@"0" forKey:@"count"];        [user synchronize];        return YES;            }}//在Appdelegate.m文件中添加如下代码- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions {//判断是不是第一次启动程序    BOOL bl = [FirstLaunchTool isFirstLaunch];    if (bl) {        NSLog(@"第一次启动");    }    else{                NSLog(@"不是第一次启动");    }//判断今天是不是第一次启动程序。    BOOL bl1 = [FirstLaunchTool isFirstLaunchOfToday];    if (bl1) {        NSLog(@"今天第一次登陆");    }    else{        NSLog(@"不是今天第一次登陆");    }    return YES;}

参考资料：

1、iOS数据持久化之使用NSUserDefaults存储数据 - IOS - 次元立方网 - 电脑知识与技术互动交流平台

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