NSUserDefaults
适用于快速读取小规模的数据
NSUserDefaults *standardDefaults = [NSUserDefaults standardUserDefaults];
写入数据
NSString *string = @"hahaha";
[standardDefaults setObject:string forKey:@"myKey"];
[standardDefaults synchronize];// 写完别忘了同步
读取数据
NSString *value = [standardDefaults objectForKey:@"myKey"];
NSUserDefaults
可以理解成键值对
有时在写数据之前,想判断下这个健是否已经设置过默认值
NSUserDefaults *standardDefaults = [NSUserDefaults standardUserDefaults];
if ([standardDefaults stringForKey:@"favoriteColor"] == nil) {
[standardDefaults setObject:@"Green" forKey:@"favoriteColor"];
[standardDefaults synchronize];
}
其实可以使用 registerDefaults:
NSUserDefaults *standardDefaults = [NSUserDefaults standardUserDefaults];
[standardDefaults registerDefaults:@{@"favoriteColor": @"Green"}];
[standardDefaults synchronize];
每次程序启动的时候调用 registerDefaults:
方法都是安全的,完全可以将这个方法的调用放到 applicationDidFinishLaunching:
方法中,这个方法永远都不会覆盖用户设置的值。
但是并不是所有类型的对象都能够直接放入 NSUserDefaults
,NSUserDefaults
只支持 Foundation
类型的对象,如果自定义 NSObject
对象存入 NSUserDefaults
就要实现 NSCoding
协议了,比如:
@interface Person : NSObject<NSCoding>
@property (nonatomic, copy) NSString *age;
@property (nonatomic, copy) NSString *name;
- (id)initWithCoder:(NSCoder *)coder;
- (void)encodeWithCoder:(NSCoder *)coder;
@implementation Person
- (id)initWithCoder:(NSCoder *)coder {
if (self = [super init]) {
self.age = [coder decodeObjectForKey:@"age"];
self.name = [coder decodeObjectForKey:@"name"];
}
return self;
}
- (void)encodeWithCoder: (NSCoder *)coder {
[coder encodeObject:self.age forKey:@"age"];
[coder encodeObject:self.name forKey:@"name"];
}
然后再存取时通过 NSData
做载体:
存入
NSUserDefaults *standardDefaults = [NSUserDefaults standardUserDefaults];
Person *person = [[Person alloc] init];
NSData *personData = [NSKeyedArchiver archivedDataWithRootObject:person];
[standardDefaults setObject:personData forKey:@"personKey"];
[standardDefaults synchronize];
读取
NSData *newPersonData = [standardDefaults objectForKey:"personKey"];
Person *Person = [NSKeyedUnarchiver unarchiveObjectWithData:newPersonData];