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深入理解iPhone数据持久化(手把手教你iphone开发 - 基础篇)

2016/08/11 11:19 [db:作者] 返回上一页

作者:孙东风 2009-11-11(请尊重作者劳动成果,转载务必注明出处)

在所有的移动开发平台数据持久化都是很重要的部分:在j2me中是rms或保存在应用程序的目录中,在symbian中可以保存在相应的磁盘目录中和数据库中。symbian中因为权限认证的原因,在3rd上大多数只能访问应用程序的private目录或其它系统共享目录。在iphone中,apple博采众长,提供了多种数据持久化的方法,下面笔者会逐个进行详细的讲解。

iphone提供的数据持久化的方法,从数据保存的方式上讲可以分为三大部分:属性列表、对象归档、嵌入式数据库(SQLite3)、其他方法。

一、属性列表NSUserDefaults

NSUserDefaults类的使用和NSKeyedArchiver有很多类似之处,但是查看NSUserDefaults的定义可以看出,NSUserDefaults直接继承自NSObject而NSKeyedArchiver 继承自NSCoder。这意味着NSKeyedArchiver实际上是个归档持久化的类,也就可以使用NSCoder类的[encodeObject: (id)objv forKey:(NSString *)key]方法来对数据进行持久化存储。

 


- (void)applicationDidFinishLaunching:(UIApplication *)application {
 NSString *strOne = @"Persistent data1";
 NSString *strTwo = @"Persistent data 2";
 
 NSMutableArray *persistentArray = [[NSMutableArray alloc] init];
 [persistentArray addObject:strOne];
 [persistentArray addObject:strTwo];
 
 //archive
 NSUserDefaults *persistentDefaults = [NSUserDefaults standardUserDefaults];
 [persistentDefaults setObject:persistentArray forKey:@"myDefault"];
 NSString *descriptionDefault = [persistentDefaults description];
 NSLog(@"NSUserDefaults description is :%@",descriptionDefault);
 
 //unarchive
 NSArray *UnpersistentArray =

[persistentDefaults objectForKey:@"myDefault"];


 NSString *UnstrOne = [UnpersistentArray objectAtIndex:0];
 NSString *UnstrTwo = [UnpersistentArray objectAtIndex:1];
 
 NSLog(@"UnstrOne = %@,UnstrTwo = %@",UnstrOne,UnstrTwo);
 
 // Override point for customization after application launch
 [window makeKeyAndVisible];
}


二、对象归档NSKeyedArchiver和NSKeyedUnarchiver

iPhone和symbian 3rd一样,会为每一个应用程序生成一个私有目录,这个目录位于

/Users/sundfsun2009/Library/Application Support/iPhone Simulator/User/Applications下,并随即生成一个数字字母串作为目录名,在每一次应用程序启动时,这个字母数字串都是不同于上一次的,上一次的应用程序目录信息被转换成名为.DS_Store隐藏文件,这个目录的文件结构如下图:

 

通常使用Documents目录进行数据持久化的保存,而这个Documents目录可以通过NSSearchPathForDirectoriesInDomains(NSDocumentDirectory,NSUserdomainMask,YES)得到,代码如下:

- (void)applicationDidFinishLaunching:(UIApplication *)application {
 NSString *strOne = @"Persistent data1";
 NSString *strTwo = @"Persistent data 2";
 
 NSArray *persistentArray = [NSArray arrayWithObjects:strOne,strTwo,nil];
 NSArray *pathArray = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory,    NSAllDomainsMask, YES);
 
 int pathLen = [pathArray count];
 
 NSLog(@"path number is :%d",pathLen);
 
 NSString *filePath;
 
 for(int i = 0; i < pathLen; i++)
 {
  filePath = [pathArray objectAtIndex:i];
  NSLog(@"%d path is :%@",i,filePath);
 }
 
 NSString *myFilename = [filePath stringByAppendingPathComponent:@"myFile.rtf"];
 
 NSLog(@"myfiles path is :%@",myFilename);
 
 // no files generated in correspond directory now
 
 [NSKeyedArchiver archiveRootObject:persistentArray toFile:myFilename];
 // now the myFile.rtf is generated
 
 // Override point for customization after application launch
 [window makeKeyAndVisible];
}

 

NSSearchPathForDirectoriesInDomains()的第二个参数是个枚举值,在笔者的测试代码中,只有NSUserDomainMask和NSAllDomainsMask可以获取到目录数为1,其余的皆为0,打印出来的结果如下:

 

[Session started at 2009-11-10 21:30:08 +0800.]
2009-11-10 21:30:10.516 PersistentExample[763:207] path number is :1
2009-11-10 21:30:10.518 PersistentExample[763:207] 0 path is :/Users/sundfsun2009/Library/Application Support/iPhone Simulator/User/Applications/C93DC783-F137-4660-AE5A-08C3E11C774B/Documents
2009-11-10 21:30:10.521 PersistentExample[763:207] myfiles path is :/Users/sundfsun2009/Library/Application Support/iPhone Simulator/User/Applications/C93DC783-F137-4660-AE5A-08C3E11C774B/Documents/myFile.rtf
Terminating in response to SpringBoards termination.

[Session started at 2009-11-10 21:32:27 +0800.]
2009-11-10 21:32:30.091 PersistentExample[803:207] path number is :1
2009-11-10 21:32:30.092 PersistentExample[803:207] 0 path is :/Users/sundfsun2009/Library/Application Support/iPhone Simulator/User/Applications/763E6772-E754-452F-8532-80C2CE4466B5/Documents
2009-11-10 21:32:30.100 PersistentExample[803:207] myfiles path is :/Users/sundfsun2009/Library/Application Support/iPhone Simulator/User/Applications/763E6772-E754-452F-8532-80C2CE4466B5/Documents/myFile.rtf
Terminating in response to SpringBoards termination.


从打印的结果如下,每次应用程序启动时生成的数字字母串目录名字并不一样。在调用[NSKeyedArchiver archiveRootObject:persistentArray toFile:myFilename]方法前,文件myFile.rtf并每生成,只有在调用此方法后才产生相应的文件。

下面需要把数据从属性列表中读取出来,在上面的代码中,笔者使用NSArray保存数据。但在大多数应用程序中,数据的尺寸并不是固定的,这个时候就需要使用NSMutalbeArray动态的保存数据,代码优化如下:

 

-          (void)applicationDidFinishLaunching:(UIApplication *)application {
 NSString *myFilename;
 // archive
 {
  NSString *strOne = @"Persistent data1";
  NSString *strTwo = @"Persistent data 2";
 
  NSMutableArray *persistentArray = [[NSMutableArray alloc] init];
  [persistentArray addObject:strOne];
  [persistentArray addObject:strTwo];

  NSArray *pathArray = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory,    NSAllDomainsMask, YES);
 
  int pathLen = [pathArray count];
  NSLog(@"path number is :%d",pathLen);
 
  NSString *filePath;
 
  for(int i = 0; i < pathLen; i++)
  {
   filePath = [pathArray objectAtIndex:i];
  
   NSLog(@"%d path is :%@",i,filePath);
  }
 
  myFilename = [filePath stringByAppendingPathComponent:@"myFile.rtf"];
 
  NSLog(@"myfiles path is :%@",myFilename);
 
  [NSKeyedArchiver archiveRootObject:persistentArray toFile:myFilename];
 }
 
 // unarchive
 {
  NSArray *unarchiveArray = [NSKeyedUnarchiver unarchiveObjectWithFile:myFilename];
  NSString *UnstrOne = [unarchiveArray objectAtIndex:0];
  NSString *UnstrTwo = [unarchiveArray objectAtIndex:1];
 
  NSLog(@"UnstrOne = %@,UnstrTwo = %@",UnstrOne,UnstrTwo);
 }
 
 
 // Override point for customization after application launch
 [window makeKeyAndVisible];
}

 

输出结果如下:

 

[Session started at 2009-11-10 22:41:57 +0800.]
2009-11-10 22:41:59.344 PersistentExample[1082:207] path number is :1
2009-11-10 22:41:59.346 PersistentExample[1082:207] 0 path is :/Users/sundfsun2009/Library/Application Support/iPhone Simulator/User/Applications/055CD17C-864E-4A83-ABF0-5F01EE85BD5A/Documents
2009-11-10 22:41:59.355 PersistentExample[1082:207] myfiles path is :/Users/sundfsu

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