屏幕快照 2016-11-17 15.33.12.png

iOS数据存取的常见方式：

1. XML属性列表(plist)归档,通常的路径是Documents
   对象是NSDictionary、NSArray,就可以使用writeToFile:atomically:方法直接将对象写到属性列表文件中

存

将数据封装成字典

NSMutableDictionary *dic = [NSMutableDictionary dictionary];
[dic setObject:@"小红" forKey:@"name"];
[dic setObject:@"15013141314" forKey:@"phone"];
[dic setObject:@"27" forKey:@"age"];
// 将字典持久化到Documents/stu.plist文件中
NSString *docPath = [NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES) lastObject];
NSString *filepath = [docPath stringByAppendingPathComponent:@"data.plist"];
[dic writeToFile:filepath atomically:YES];
// 或者是数组
// 注意:如果为YES则保证文件的写入原子性,就是说会先创建一个临时文件,直到文件内容写入成功再导入到目标文件里.
// 如果为NO,则直接写入目标文件里. 

读

读取Documents/stu.plist的内容，实例化NSDictionary或者NSArray

NSString *docPath = [NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES) lastObject];
NSString *filepath = [docPath stringByAppendingPathComponent:@"data.plist"
];
NSDictionary *dic = [NSDictionary dictionaryWithContentsOfFile:path];
NSLog(@"name:%@", [dict objectForKey:@"name"]);
NSLog(@"phone:%@", [dict objectForKey:@"phone"]);
NSLog(@"age:%@", [dict objectForKey:@"age"]);
// 如果写入的是数组，就用下面的方法取值
NSArray *array= [NSArray arrayWithContentsOfFile:filepath];

2. preference(偏好设置): 直接写到Library/Preferences:目录下面;保存用户名、字体大小、是否自动登录.

存

NSUserDefaults *defaults = [NSUserDefaults standardUserDefaults];
[defaults setObject:@"itcast" forKey:@"username"];
[defaults setFloat:18.0f forKey:@"text_size"];
[defaults setBool:YES forKey:@"auto_login"];
// 注意：UserDefaults设置数据时，不是立即写入，而是根据时间戳定时地把缓存中的数据写入本地磁盘。所以调用了set方法之后数据有可能还没有写入磁盘应用程序就终止了，因此要调用synchronize方法强制写入
[defaults synchronize];

读

NSUserDefaults *defaults = [NSUserDefaults standardUserDefaults];
NSString *username = [defaults stringForKey:@"username"];
float textSize = [defaults floatForKey:@"text_size"];
BOOL autoLogin = [defaults boolForKey:@"auto_login"];

3. NSKeyedArchiver归档(NSCoding):可以存储对象
   (1) NSString、NSDictionary、NSArray、NSData、NSNumber等类型，可以直接用NSKeyedArchiver进行归档和恢复
   (2)不是所有的对象都可以直接用这种方法进行归档，只有遵守了<NSCoding>协议的对象才可以;
   (3).NSCoding协议有2个方法:
   一是:
   encodeWithCoder:每次归档对象时，都会调用这个方法,一般在这个方法里面指定如何归档对象中的每个实例变量，encodeObject:forKey:方法归档实例变量;
   二是：
   initWithCoder:每次从文件中恢复(解码)对象时，都会调用这个方法。一般在这个方法里面指定如何解码文件中的数据为对象的实例变量，可以使用decodeObject:forKey方法解码实例变量;

// 首先要对对象实行下面方法:
- (void)encodeWithCoder:(NSCoder *)encoder{   
 [encoder encodeObject:self.no forKey:@"no"];   
 [encoder encodeInt:self.age forKey:@"age"];    
 [encoder encodeDouble:self.height forKey:@"height"];   
}
- (id)initWithCoder:(NSCoder *)decoder
{    if (self = [super init]) {        
// 读取文件的内容        
self.no = [decoder decodeObjectForKey:@"no"];        
self.age = [decoder decodeIntForKey:@"age"];        
self.height = [decoder decodeDoubleForKey:@"height"];    
}   
 return self;
}

存

NSString *doc = [NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES) lastObject];    
// 获得文件的全路径    
NSString *path = [doc stringByAppendingPathComponent:@"xxx.data"];
//将对象归档
[NSKeyedArchiver archiveRootObject:stu toFile:path];

读

NSString *doc = [NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES) lastObject];
NSString *path = [doc stringByAppendingPathComponent:@"xxx.data"];
Student *stu = [NSKeyedUnarchiver unarchiveObjectWithFile:path];

存取对象数组

存

 NSMutableArray *itemsDataArray = [NSMutableArray array];    
 for (RWTItem *item in self.items) {        
NSData *itemData = [NSKeyedArchiver archivedDataWithRootObject:item];        
[itemsDataArray addObject:itemData];    
}
    [[NSUserDefaults standardUserDefaults] setObject:itemsDataArray forKey:kRWTStoredItemsKey];
    [[NSUserDefaults standardUserDefaults] synchronize];

读

 NSArray *storedItems = [[NSUserDefaults standardUserDefaults] arrayForKey:kRWTStoredItemsKey];    
self.items = [NSMutableArray array];    
if (storedItems) {        
for (NSData *itemData in storedItems) {            
RWTItem *item = [NSKeyedUnarchiver unarchiveObjectWithData:itemData];            
[self.items addObject:item];  
}
}