obj-c编程13:归档

    这篇归档内容的博文也挺有趣的，笨猫对好玩的东西一向感兴趣啊！如果用过ruby就会知道，obj-c里的归档类似于ruby中的序列化概念，不过从语法的简洁度来说，我只能又一次呵呵了。 下面大家将会看到2种归档数据的方法：属性列表和带键值的编码，前者可以理解为简单的类似字典（比如还有数组）对象的归档，而后者可以实现任意对象的归档化哦。我们依次道来吧。

1. 属性列表(plists)

    os x上的程序使用类似字典类概念为支持的XML属性列表（或plists）存储默认参数等配置信息之类的数据，以前“老式”的属性列表数据格式不是XML，现在我们一般都用XML格式啊。属性列表不仅可以是NSDictionary对象，还可以是NSString、NSArray、NSData或是NSNumber类型，可以使用这些类中实现的writeToFile:atomically方法将数据写到文件中去。特别的如果是字典或数组的情况下，保存到文件的格式是XML属性列表格式哦。

#import <Foundation/Foundation.h>#define msg(...) NSLog(__VA_ARGS__)int main(int argc,char *argv[]){@autoreleasepool{NSDictionary *dict = [NSDictionary dictionaryWithObjectsAndKeys:\@"val0",@"key0",@"val1",@"key1",@"val2",@"key2",nil];NSDictionary *dict_from_file;//归档if([dict writeToFile:@"data.db" atomically:YES] == NO)msg(@"save to file failed!");//读档dict_from_file = [NSDictionary dictionaryWithContentsOfFile:\@"data.db"];msg(@"%@",dict_from_file);}return 0;}

其中atomically参数是一种保护措施，如果被设为YES，则现将字典内容写入临时备份文件中去，成功后才最终将数据写入指定文件data.db中去。我们看一下返回结果：

apple@kissAir: objc_src$./gd

2014-07-03 15:32:43.263 gd[1991:507] {

    key0 = val0;

    key1 = val1;

    key2 = val2;

}

apple@kissAir: objc_src$cat data.db

<?xml version="1.0" encoding="UTF-8"?>

<!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">

<plist version="1.0">

<dict>

<key>key0</key>

<string>val0</string>

<key>key1</key>

<string>val1</string>

<key>key2</key>

<string>val2</string>

</dict>

</plist>

很简单，是吧？如果要在跨平台程序中使用属性列表，可以查看一下NSPropertyListSerialization类，使用该类在文件中读写属性列表可以在不同平台之间移植。

2.带键值的编码归档

接下来看一看比简单的属性列表稍微复杂，但也更加通用的带键值的编码归档方法。这就是利用NSKeyedArchiver类创建带键（keyed）的档案来完成，它是从os x 10.2开始支持的哦。在此之前是使用NSArchiver类创建连续的（sequential）归档，这有个不方便的地方：连续归档需要完全按写入时的顺序读取归档中的数据。下面我们来看看，对于简单的字典对象如何归档和读档喽：

#import <Foundation/Foundation.h>#define msg(...) NSLog(__VA_ARGS__)int main(int argc,char *argv[]){@autoreleasepool{NSDictionary *dict = [NSDictionary dictionaryWithObjectsAndKeys:\@"val0",@"key0",@"val1",@"key1",@"val2",@"key2",nil];NSDictionary *dict_from_file;//归档if([NSKeyedArchiver archiveRootObject:dict toFile:@"data.archive"] == NO)msg(@"save to file failed!");//读档//dictionaryWithContentsOfFile如果失败会引发异常，这个和以前的返回NO不一样哦。dict_from_file = [NSKeyedUnarchiver unarchiveObjectWithFile:\@"data.archive"];msg(@"%@",dict_from_file);}return 0;}

运行结果如下：

apple@kissAir: objc_src$./gd

2014-07-03 15:47:02.411 gd[2017:507] {

    key0 = val0;

    key1 = val1;

    key2 = val2;

}

apple@kissAir: objc_src$cat data.archive

bplist00?!"X$versionX$objectsY$archiverT$top??$null?

???????Tkey1Tkey0Tkey2Tval1Tval0Tval2?Z$classnameX$classes\NSDictionary? XNSObject_NSKeyedArchiver?#$Troot#-27AGNVahlnprvxz|~???????????????%?

注意如果查看data.archive文档会发现其不是人类可读的文档格式，而是类似于一种二进制格式哦。

    上面这些归档和读档方法是很不错，但是想要直接用在我们自己的类中，没门啊！因为编译器不知道我们自己的类以何种表示方式归档呢。所以聪明的童鞋一定猜到了方法，在类中添加自己的归档和读档方法吧！

    要归档自己的对象，必须遵守<NSCoding>协议，在类中添加encodeWithCoder和initWithCoder方法，前者用来归档，后者自然是读档啦。下面我们构造2个类Player和Skill类，不同的球员自然有不同的技能啦，比如司令塔，钢铁防线什么的...貌似要跑题啊！STOP！大家直接看代码吧，虽然比较长，但注释钢钢的啊:

#import <Foundation/Foundation.h>#define msg(...) NSLog(__VA_ARGS__)@interface Skill:NSObject <NSCoding>//maybe <NSCoding,NSCopying> :)@property NSString *name;@property int level;-(id)init:(NSString*)name :(int)level;-(NSString*)description;-(void)use;@end@implementation Skill@synthesize name,level;-(id)init:(NSString*)name_v :(int)level_v{self = [super init];if(self){name = name_v;level = level_v;}return self;}-(NSString*)description{return [NSString stringWithFormat:@"[skill:%@ , level:%i]",name,level];}-(void)use{msg(@"%@ is used!!!",self);}-(void)encodeWithCoder:(NSCoder *)encoder{[encoder encodeObject: name forKey:@"Skill#name"];[encoder encodeInt: level forKey:@"Skill#level"];}-(id)initWithCoder:(NSCoder *)decoder{name = [decoder decodeObjectForKey:@"Skill#name"];level = [decoder decodeIntForKey:@"Skill#level"];return self;}@end@interface Player:NSObject <NSCoding>@property NSString *name;@property int number;@property NSMutableArray *skills;-(NSString*)description;@end@implementation Player@synthesize name,number,skills;-(id)init{//需要为skills对象分配空间啊！否者skills打印的是NULLself = [super init];if(self){skills = [[NSMutableArray alloc] init];}return self;}-(NSString*)description{return [NSString stringWithFormat:@"[%@:NO.%i] skills:\n%@",\name,number,skills];}-(void)encodeWithCoder:(NSCoder *)encoder{[encoder encodeObject: name forKey:@"Player#name"];[encoder encodeInt: number forKey:@"Player#number"];[encoder encodeObject: skills forKey:@"Player#skills"];}-(id)initWithCoder:(NSCoder *)decoder{name = [decoder decodeObjectForKey:@"Player#name"];number = [decoder decodeIntForKey:@"Player#number"];skills = [decoder decodeObjectForKey:@"Player#skills"];return self;}@endint main(int argc,char *argv[]){@autoreleasepool{Player *p0 = [[Player alloc] init];Skill *s0 = [[Skill alloc] init:@"super_lead" :3];//司令塔Skill *s1 = [[Skill alloc] init:@"steel_defend" :2];//钢铁防守Skill *s2 = [[Skill alloc] init:@"steal_master" :2];//抢断大师Skill *s3 = [[Skill alloc] init:@"spiritual_leader" :1];//精神领袖p0.name = @"messi";p0.number = 10;//利用数组的addObject方法加入每个技能[p0.skills addObject:s0];[p0.skills addObject:s1];[p0.skills addObject:s2];[p0.skills addObject:s3];msg(@"%@",p0);//像单个对象那样归档吧if([NSKeyedArchiver archiveRootObject:p0 toFile:@"player.arch"] == NO)msg(@"save to archiving failed!");//像单个对象那样读档吧Player *p1 = [NSKeyedUnarchiver unarchiveObjectWithFile:@"player.arch"];msg(@"%@",p1);}return 0;}

例子比较长，但很简单哦，运行结果如下：

apple@kissAir: objc_src$./gd

2014-07-03 17:00:15.623 gd[2260:507] [messi:NO.10] skills:

(

    "[skill:super_lead , level:3]",

    "[skill:steel_defend , level:2]",

    "[skill:steal_master , level:2]",

    "[skill:spiritual_leader , level:1]"

)

2014-07-03 17:00:15.626 gd[2260:507] [messi:NO.10] skills:

(

    "[skill:super_lead , level:3]",

    "[skill:steel_defend , level:2]",

    "[skill:steal_master , level:2]",

    "[skill:spiritual_leader , level:1]"

)

    我们还可以把任意多个对象归档到文件中去，这就用到了内存归档技术啦，即使用NSData的通用数据流对象类，可以实现上述功能哦！注意这个类似乎很熟悉吧？对啊，在第10[3]和10[4]文件管理篇里有提到啊！

    NSData可以用来保留一块内存空间来存储数据，以便随后写入文件或存放从文件读取的内容。以下语句创建一个空缓冲区，其大小将随着程序执行需要而扩展:

buf = [NSMutableData data];

下面将演示如何在一个归档和读档多个对象（只列出在上个代码基础上新添加的部分，否则太长）：

NSDictionary *dict = [NSDictionary dictionaryWithObjectsAndKeys:\@"val0",@"key0",@"val1",@"key1",@"val2",@"key2",nil];NSMutableData *buf = [NSMutableData data];NSKeyedArchiver *arch = [[NSKeyedArchiver alloc] \initForWritingWithMutableData: buf];//将Player对象和字典对象一起归档[arch encodeObject:p0 forKey:@"Player"];[arch encodeObject:dict forKey:@"Dict"];//结束在buf中添加对象，我称之为“封口”[arch finishEncoding];//归档写入文件if([buf writeToFile: @"mobjs.arch" atomically:YES] == NO){msg(@"arch to file failed!");return 1;}//将Player对象和字典对象一起读档（解档）NSData *buf_read = [NSData dataWithContentsOfFile:@"mobjs.arch"];if(!buf_read){msg(@"read file : mobjs.arch failed!");return 2;}NSKeyedUnarchiver *unarch = [[NSKeyedUnarchiver alloc] \initForReadingWithData: buf_read];Player *p2 = [unarch decodeObjectForKey:@"Player"];NSDictionary *dict1 = [unarch decodeObjectForKey:@"Dict"];//别忘了也要完成一下哦[unarch finishDecoding];msg(@"dict:%@",dict1);msg(@"player:%@",p2);

运行结果如下：

2014-07-03 17:34:23.090 gd[2362:507] dict:{

    key0 = val0;

    key1 = val1;

    key2 = val2;

}

2014-07-03 17:34:23.091 gd[2362:507] player:[messi:NO.10] skills:

(

    "[skill:super_lead , level:3]",

    "[skill:steel_defend , level:2]",

    "[skill:steal_master , level:2]",

    "[skill:spiritual_leader , level:1]"

)

    我们还可以利用归档功能来完成对象的深拷贝，其实前面代码里已经有了哦。不过还是简单贴一下代码吧：

#import <Foundation/Foundation.h>#define msg(...) NSLog(__VA_ARGS__)#define mstr(x) [NSMutableString stringWithString:x]int main(int argc,char *argv[]){@autoreleasepool{NSData *buf;NSMutableArray *ary1 = [NSMutableArray arrayWithObjects:\mstr(@"one"),mstr(@"two"),mstr(@"three"),nil];NSMutableArray *ary2;NSMutableString *mstr;//使用归档进行深拷贝,没有实际读取文件，走的是内存路线啊！buf = [NSKeyedArchiver archivedDataWithRootObject: ary1];ary2 = [NSKeyedUnarchiver unarchiveObjectWithData: buf];mstr = [ary2 objectAtIndex:0];[mstr appendString:@"_fixed"];msg(@"%@\n****************************%@",ary1,ary2);}return 0;}

运行结果如下：

apple@kissAir: objc_src$./6

2014-07-03 17:45:58.972 6[2414:507] (

    one,

    two,

    three

)

****************************(

    "one_fixed",

    two,

    three

)