对象归档

文章目录

1. 1. 使用NSKeyedArchiver归档
2. 2. 实现NSCoding协议
3. 3. 使用NSData完成自定义归档

• 归档就是用户某种格式把一个或者多个对象保存到指定的文件中，方便以后从文件中恢复它们。

使用NSKeyedArchiver归档

• NSKeyedArchiver负责将对象归档到指定文件中
• NSKeyedUnarchiver则负责从文件中恢复对象
  • 直接调用archivedDataWithRootObject:data、archiveRootObject:toFile:file类方法将指定对象作为root进行归档；恢复时，则调用NSKeyedUnarchiver的unarchiveObjectWithData:data或者unarchiveObjectWithFile:file类方法。

  // 归档
  NSDictionary* dict = [NSDictionary dictionaryWithObjectsAndKeys:
      [NSNumber numberWithInt:89],@"objc",
      [NSNumber numberWithInt:88],@"cpp",
      [NSNumber numberWithInt:87],@"java",
      nil];
  [NSKeyedArchiver archiveRootObject:dict toFile:@"myDict.archive"];

  // 恢复
  NSDictionary* dict = [NSKeyedUnarchiver unarchiveObjectWithFile:@"myDict.archive"];
  NSLog("%d",[dict valueForKey:@"objc"]);
  NSLog("%d",[dict valueForKey:@"cpp"]);
  NSLog("%d",[dict valueForKey:@"java"]);

实现NSCoding协议

• 自定义类要实现归档、恢复，应该实现NSCoding协议，必须实现该协议中的定义的如下两个方法
  • initWithCoder:该方法负责恢复对象
  • encodeWithCoder:该方法负责归档对象
• 归档和恢复基本数据类型

归档数据	恢复数据
encodeBool:forKey	decodeBoolForKey
encodeInt:forKey	decodeIntForKey
encodeInt32:forKey	decodeInt32ForKey
encodeInt64:forKey	decodeInt64ForKey
encodeFloat:forKey	decodeFloatForKey
encodeDouble:forKey	decodeDoubleForKey

• 示例

# import <Foundation/Foundation.h>
@interface ZTApple : NSObject <NSCoding>
@property (nonatomic,copy) NSString* color;
@property (nonatomic,assign)double weight;
@property (nonatomic,assign)int size;
- (id) initWithColor:(NSString*) color weight:(double) weight size:(int) size;
@end

# import "ZTApple.h"
@implementation ZTApple
@synthesize color = _color;
@synthesize weight = _weight;
@synthesize size = _size;
-(id) initWithColor:(NSString*) color weight:(double) weight size:(int) size
{
    if(self = [super init])
    {
        self.color = color;
        self.weight = weight;
        self.size = size;
    }
    return self;
} 
-(NSString *)description
{
    return [NSString stringWithFormat:"@<ZTApple[_color=%@,_weigt=%g,_size=%d]>",self.color,self.weight,self.size];
}
-(void) encodeWithCoder:(NSCode*) coder
{
    [coder encodeOject:_color forKey:@"color"];
    [coder encodeDouble:_weight foeKey:@"weight"];
    [coder encodeInt:_size forKey:@"size"];
}
-(void) initWithCoder:(NSCoder*) coder
{
    _color = [coder decodeObjectForKey:@"color"];
    _weight = [coder decodeDoubleForkey:@"weight"];
    _size = [coder decodeIntForKey:@"size"];
    return self;
}
@end

使用NSData完成自定义归档

• 一次性收集多个对象，并将这些对象归档到单个文件中，此时借助NSMutableData来创建NSKeyedArchiver或NSKeyedUnarchiver对象。
• 归档过程

1. 以NSMutableData作为参数，创建NSKeyedArchiver对象。
2. 反复调用NSKeyedArchiver对象的encodeXxx:forKey:方法来归档所有需要归档到一个文件的对象。
3. 调用NSKeyedArchiver对象的finishEncoding方法来结束归档。
4. 根据需要，程序可以选择将保存归档数据的NSMutableData通过网络或输出到磁盘文件上。

NSDictionary* dict = [NSDictionary dictionaryWithObjectsAndKeys:
    [NSNumber numberWithInt:66],@"objc",
    [NSNumber numberWithInt:76],@"c++",
    [NSNumber numberWithInt:86],@"java",nil];
NSSet* set = [NSSet setWithObjects:
    @"test1",@"test2",@"test3",nil];
ZTApple* apple = [[ZTApple alloc] initWithColor:@"红色" weight:3.4 size:20];
NSMutableData* data = [[NSMutableData data];
NSKeyedArchiver* arch = [[NSKeyedArchiver alloc] initForWritingWithMutableData:data];
[arch encodeObject:dict forKey:@"dict"];
[arch encodeObject:set forKey:@"set"];
[arch encodeObject:apple forKey:@"apple"];
[arch finishEncoding];
if([data writeToFile:@"multi.archive" atomically:YES] == NO)
{
    NSLog("归档失败");
}

• 恢复过程

1. 以NSData作为参数，创建NSkeyedUnarchiver对象
2. 重复调用NSKeyedUnarchiver对象的decodeXxx:forKey:方法从文件中恢复所有归档过的对象
3. 调用NSKeyedUnarchiver对象的finishDecoding方法结束恢复

NSData* data = [NSData dataWithContentsOfFile:@"multi.archive"];
NSKeyedUnarchiver* unarch = [[NSKeyedUnarchiver alloc] initForReadingWithData:data];
NSDictionary* dict = [unarch decodeObjectForKey:@"dict"];
NSSet* set = [unarch decodeObjectForKey:@"set"];
NSApple* apple = [unarch decodeObjectForKey:@"apple"];
[unarch finishDecoding];