iOS存储的三种方式

iOS中存储的3中方式：

1.NSUserDefaults

注意存储基本对象类型是没有问题的，但是要存储自定义对象，则要将对象内所有的属性（或是需要存储的属性）序列化，实现NSCoding协议序列化。

存：
[[NSUserDefaults standardUserDefaults] setValue:@"yellow" forKey:@"color"];

[[NSUserDefaults standardUserDefaults] synchronize];

取：
NSString *color = [[NSUserDefaults standardUserDefaults] objectForKey:@"color"];

 对于存储的是自定义的对象：（示例Contact的序列化）

#import <Foundation/Foundation.h>

@interface Contact : NSObject <NSCoding>

@property (nonatomic,retain) NSString *name;
@property (nonatomic,retain) NSString *phoneNumber;

+ (id)contactsWithName:(NSString *)aName phoneNumber:(NSString *)aPhoneNumber;

@end

#import "Contact.h"

#define kNameKey  @"NameKey"
#define kPhoneNumberKey  @"PhoneNumberKey"

@implementation Contact

- (id)initWithName:(NSString *)aName phoneNumber:(NSString *)aPhoneNumber
{
    if (self = [super init])
    {
        self.name = aName;
        self.phoneNumber = aPhoneNumber;
    }
    
    return self;
}

//初始化配套的便利方法  ,静态方法中的self 不代表当前类的对象，代表当前类本身
+ (id)contactsWithName:(NSString *)aName phoneNumber:(NSString *)aPhoneNumber
{
    return [[[self alloc] initWithName:aName phoneNumber:aPhoneNumber] autorelease];
    
}

//对象序列化的两个协议方法

//对象序列化的方法,把对象的所有属性编码到本地
- (void)encodeWithCoder:(NSCoder *)aCoder
{
    [aCoder encodeObject:_name forKey:kNameKey];
    [aCoder encodeObject:_phoneNumber forKey:kPhoneNumberKey];
}

//对象反序列化的方法
- (id)initWithCoder:(NSCoder *)aDecoder
{
    if(self = [super init])
    {
        self.name = [aDecoder decodeObjectForKey:kNameKey];
        self.phoneNumber = [aDecoder decodeObjectForKey:kPhoneNumberKey];
    }
    
    return self;
}

2.沙盒

- (void)viewDidLoad 
{
    [super viewDidLoad];
    
    NSMutableDictionary *savedDic = [[NSMutableDictionary alloc] initWithContentsOfFile:[self dataFilePath]];
    
    //如果第一次进入，从userdefault中取不到数据，手动创建一个字典
    if (!savedDic)
    {
        self.dic = [NSMutableDictionary dictionaryWithCapacity:0];
    }
    else 
    {
        self.dic = savedDic;
    }
    //注册一个即将进入后台的通知
    [[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(saveData) name:UIApplicationWillResignActiveNotification object:nil];
    
}

//返回文件的路径
- (NSString *)dataFilePath
{
    //沙盒
    //获得沙盒下面Documents文件夹的路径
    NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);
    NSLog(@"paths   %@",paths);
    NSString *path = [paths objectAtIndex:0];
    //在documents 路径下，追加一个文件路径
    NSString *filePath = [path stringByAppendingPathComponent:@"select.plist"];
    
    return filePath;           
}

- (void)saveData
{
    //字典当中存储的value 必须是  array dictionary Boolean data date nsnumber nsstring
    //把一个字典写到文件中，实际上是按照plist 的格式去组织数据的
    [_dic writeToFile:[self dataFilePath] atomically:YES];
    NSMutableDictionary *savedDic = [[NSMutableDictionary alloc] initWithContentsOfFile:[self dataFilePath]];
}

3.sqlite