iOS开发 数据持久化－归档

在iOS开发过程中，很多时候都需要进行一些数据的储存和读入，在数据量不大的情况下，使用plist储存数据是一种很方便的方式，但是plist只能允许储存一些系统自带的数据类型，如果需要储存自定义的数据类型，plist是是用不了的，但是可以使用另外一种数据持久化的方法－对象归档。



NSCoding协议

要想使用对象归档，需要归档的对象就要实现NSCoding协议，实现NSCoding协议需要实现它的两个方法：

- (void)encodeWithCoder:(NSCoder *)aCoder;//写入数据
- (id)initWithCoder:(NSCoder *)aDecoder;//读取数据

我们可以将对象的属性写入NSCoder对象中，也可以从其中读取写入的数据，NSCoder中包含了许多方法，其中：

- (void)encodeObject:(id)objv forKey:(NSString *)key;
- (void)encodeBool:(BOOL)boolv forKey:(NSString *)key;
- (void)encodeInt:(int)intv forKey:(NSString *)key;
- (void)encodeInt32:(int32_t)intv forKey:(NSString *)key;
- (void)encodeInt64:(int64_t)intv forKey:(NSString *)key;
- (void)encodeFloat:(float)realv forKey:(NSString *)key;
- (void)encodeDouble:(double)realv forKey:(NSString *)key;

可以将各种类型的对象写入到NSCoder对象中，并将其与key关联起来，而：

- (id)decodeObjectForKey:(NSString *)key;
- (BOOL)decodeBoolForKey:(NSString *)key;
- (int)decodeIntForKey:(NSString *)key;
- (int32_t)decodeInt32ForKey:(NSString *)key;
- (int64_t)decodeInt64ForKey:(NSString *)key;
- (float)decodeFloatForKey:(NSString *)key;
- (double)decodeDoubleForKey:(NSString *)key;

则可以将NSCoder中的对象使用key读取出来。



对象归档

而归档对象，需要使用

[NSKeyedArchiver archiveRootObject:object toFile:path];

将object对象归档到path文件中。逆归档则需要使用

[NSKeyedUnarchiver unarchiveObjectWithFile:path];

将path文件中的对象读取出来。

基本的对象归档流程就是这样，之后是我的一个示例：

//StudentModel.h

#import <Foundation/Foundation.h>

@interface StudentModel : NSObject <NSCoding>

@property (nonatomic, strong) NSString*     name;
@property (nonatomic, strong) NSString*     stuID;
@property (nonatomic, assign) NSInteger     age;

@end

//StudentModel.m

#import "StudentModel.h"

@implementation StudentModel

#pragma mark -- NSCoding
- (instancetype)initWithCoder:(NSCoder *)aDecoder
{
    self = [super init];
    if (self) {
        self.name  = [aDecoder decodeObjectForKey:@"name"];
        self.stuID = [aDecoder decodeObjectForKey:@"stuID"];
        self.age   = [aDecoder decodeIntegerForKey:@"age"];
    }
    return self;
}

- (void)encodeWithCoder:(NSCoder *)aCoder
{
    [aCoder encodeObject:self.name forKey:@"name"];
    [aCoder encodeObject:self.stuID forKey:@"stuID"];
    [aCoder encodeInteger:self.age forKey:@"age"];
}

@end

//ViewController.m

#import "ViewController.h"
#import "StudentModel.h"

@interface ViewController ()
{
    StudentModel*      _myStudent;
    StudentModel*      _myStudent1;
    NSString*          _path;
}

@end

@implementation ViewController

- (void)viewDidLoad {
    [super viewDidLoad];
    // Do any additional setup after loading the view, typically from a nib.
    
    NSString *Path = [NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES) objectAtIndex:0];
    _path = [Path stringByAppendingPathComponent:@"test"];
    
    _myStudent = [[StudentModel alloc] init];
    _myStudent.name = @"小明";
    _myStudent.stuID = @"20121001047";
    _myStudent.age = 21;
    [self archivedStudent];
}

#pragma mark -- response
- (IBAction)touchUnarchiveBtn:(id)sender {
    [self unarchivedStudent];
}

#pragma mark -- method
- (void)archivedStudent
{
    [NSKeyedArchiver archiveRootObject:_myStudent toFile:_path];
}

- (void)unarchivedStudent
{
    _myStudent1 = [NSKeyedUnarchiver unarchiveObjectWithFile:_path];
    NSLog(@"name:%@", _myStudent1.name);
    NSLog(@"studentID:%@", _myStudent1.stuID);
    NSLog(@"age:%d", (int)_myStudent1.age);
}

@end

附上打印结果：

2015-07-26 09:04:06.163 NSCodingTest[7679:7139551] name:小明
2015-07-26 09:04:06.164 NSCodingTest[7679:7139551] studentID:20121001047
2015-07-26 09:04:06.165 NSCodingTest[7679:7139551] age:21