理解IOS数据持久化

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)、

其他方法如cocoadata。

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:persistentArrayforKey:@"myDefault"];
 NSString *descriptionDefault =[persistentDefaults description];
 NSLog(@"NSUserDefaults description is:%@",descriptionDefault);
 
 //unarchive
 NSArray *UnpersistentArray =

[persistentDefaultsobjectForKey:@"myDefault"];

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

二、对象归档NSKeyedArchiver和NSKeyedUnarchiver

iPhone和symbian3rd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/iPhoneSimulator/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 = [NSArrayarrayWithObjects: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 = [filePathstringByAppendingPathComponent:@"myFile.rtf"];
 
 NSLog(@"myfile's path is :%@",myFilename);
 
 // no files generated in correspond directorynow
 
 [NSKeyedArchiverarchiveRootObject:persistentArray toFile:myFilename];
 // now the myFile.rtf is generated
 
 // Override point for customization afterapplication 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 2009-11-1021:30:08 +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/iPhoneSimulator/User/Applications/C93DC783-F137-4660-AE5A-08C3E11C774B/Documents
2009-11-10 21:30:10.521 PersistentExample[763:207] myfile's path is:/Users/sundfsun2009/Library/Application Support/iPhoneSimulator/User/Applications/C93DC783-F137-4660-AE5A-08C3E11C774B/Documents/myFile.rtf
Terminating in response to SpringBoard's termination.

[Session started at 2009-11-1021:32:27 +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/iPhoneSimulator/User/Applications/763E6772-E754-452F-8532-80C2CE4466B5/Documents
2009-11-10 21:32:30.100 PersistentExample[803:207] myfile's path is:/Users/sundfsun2009/Library/Application Support/iPhoneSimulator/User/Applications/763E6772-E754-452F-8532-80C2CE4466B5/Documents/myFile.rtf
Terminating in response to SpringBoard's 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[NSKeyedArchiverarchiveRootObject:persistentArraytoFile: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 = [pathArrayobjectAtIndex:i];
  
   NSLog(@"%d path is:%@",i,filePath);
  }
 
  myFilename = [filePathstringByAppendingPathComponent:@"myFile.rtf"];
 
  NSLog(@"myfile's path is :%@",myFilename);
 
  [NSKeyedArchiverarchiveRootObject:persistentArray toFile:myFilename];
 }
 
 // unarchive
 {
  NSArray *unarchiveArray = [NSKeyedUnarchiverunarchiveObjectWithFile:myFilename];
  NSString *UnstrOne = [unarchiveArrayobjectAtIndex:0];
  NSString *UnstrTwo = [unarchiveArrayobjectAtIndex:1];
 
  NSLog(@"UnstrOne = %@,UnstrTwo = %@",UnstrOne,UnstrTwo);
 }
 
 
 // Override point for customization afterapplication launch
 [window makeKeyAndVisible];
}

 

输出结果如下：

 

[Session started at 2009-11-1022:41:57 +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/iPhoneSimulator/User/Applications/055CD17C-864E-4A83-ABF0-5F01EE85BD5A/Documents
2009-11-10 22:41:59.355 PersistentExample[1082:207] myfile's pathis :/Users/sundfsun2009/Library/Application Support/iPhoneSimulator/User/Applications/055CD17C-864E-4A83-ABF0-5F01EE85BD5A/Documents/myFile.rtf
2009-11-10 22:41:59.357 PersistentExample[1082:207] UnstrOne =Persistent data1,UnstrTwo = Persistent data 2
Terminating in response to SpringBoard's termination.

从上面的图中可以看到，目录中还有个tmp目录，读者也可以把数据保存在tmp目录中，获取这个目录使用NSTemporaryDirectory()方法。

三、嵌入式数据库(SQLite3)

嵌入式数据库持久化数据就是把数据保存在iphone的嵌入式数据库系统SQLite3中，本质上来说，数据库持久化操作是基于文件持久化基础之上的。
要使用嵌入式数据库SQLite3，首先需要加载其动态库libsqlite3.dylib，这个文件位于/Xcode3.1.4/Platforms/iPhoneOS.platform/Developer/SDKs/iPhoneOS3.1.sdk/usr/lib目录下。在Framework文件夹上右击，选择“Adding->ExistingFiles...”，定位到上述目录并加载到文件夹。

首先在头文件中做如下修改：

 

#import<UIKit/UIKit.h>

#include "sqlite3.h"
#define kFileName @"mydb.sql"

@interfacePersistentExampleAppDelegate : NSObject<UIApplicationDelegate> {
 sqlite3 *database;
 UIWindow *window;
}

@property (nonatomic, retain)IBOutlet UIWindow *window;

@end

 

 

- (void)applicationDidFinishLaunching:(UIApplication *)application{
 
 NSArray *path =NSSearchPathForDirectoriesInDomains(NSDocumentDirectory,NSUserDomainMask, YES);
 NSString *paths = [[path objectAtIndex:0]stringByAppendingPathComponent:kFileName];
 
 NSFileManager *fileManager = [NSFileManagerdefaultManager];
 BOOL findFile = [fileManagerfileExistsAtPath:paths];
 
 NSLog(@"Database file path =%@",paths);
 
 // 如果找到了数据库文件
 if(findFile)
 {
  NSLog(@"Database file have alreadyexisted.");
 
  if(sqlite3_open([paths UTF8String],&database) != SQLITE_OK)//打开数据库失败
  {
   sqlite3_close(database);
   NSAssert(0,@"Failed to opendatabase");
  }
 }else
 {
  NSLog(@"Database file does not exsit!");
  if(sqlite3_open([paths UTF8String],&database) != SQLITE_OK)//打开数据库失败
  {
   sqlite3_close(database);
   NSAssert(0,@"Failed to opendatabase");
  }
 }
 
 char *errorMsg;

 

//创建表
 NSString *createSQL = @"create table if notexists fields (row integer primary key, field_data text);";
 if(sqlite3_exec(database, [createSQLUTF8String],NULL,NULL,&errorMsg)!=SQLITE_OK)
 {
  sqlite3_close(database);
  NSAssert1(0,@"Error creating table:%s",errorMsg);
 }
 
 NSString *strOne = @"Persistent data1";
 NSString *strTwo = @"Persistent data 2";
 
 NSMutableArray *persistentArray =[[NSMutableArray alloc] init];
 [persistentArray addObject:strOne];
 [persistentArray addObject:strTwo];
 
 for (int i = 0; i <[persistentArray count]; i++) {
  NSString *upDataSQL = [[NSString alloc]initWithFormat:@"insert or replace into

fields (row,field_data) values(%d,'%@');",i,[persistentArray objectAtIndex:i]];

  char* errorMsg;
  if(sqlite3_exec(database,[upDataSQLUTF8String],NULL,NULL,&errorMsg)

!= SQLITE_OK)
  {
   sqlite3_close(database);
   NSAssert(0,@"Failed to opendatabase");
  }
 }
 
 //unarchive
 NSString *query = @"select row, field_data fromfields order by row";//查找表中的数据
 sqlite3_stmt *statement;
 if(sqlite3_prepare_v2(database, [queryUTF8String], -1, &statement, nil)

== SQLITE_OK)
 {
  while(sqlite3_step(statement) ==SQLITE_ROW)
  {
   int row =sqlite3_column_int(statement, 0);
   char *rowData = (char*)sqlite3_column_text(statement, 1);
  
   NSString *fieldName =[[NSString alloc] initWithFormat:@"show%d",row];
   NSString *fieldValue =[[NSString alloc] initWithUTF8String:rowData];

   NSLog(@"fieldName is:%@,fieldValue is :%@",fieldName,fieldValue);
  
   [fieldName release];
   [fieldValue release];
  }
  sqlite3_finalize(statement);
 }
 
 // Override point for customization afterapplication launch
 [window makeKeyAndVisible];
}

在上面的代码中，我们使用
NSFileManager *fileManager = [NSFileManager defaultManager];
BOOL findFile = [fileManager fileExistsAtPath:paths];
来判断数据库文件是否已经存在，其实在大多数情况下是没有必要的，sqlite3_open()方法会自动帮我们判断数据库文件是否存在，如果不存在则创建心的数据库文件。

四、其它方法

除了上面的三种方法来保存持久化数据以外，我们还可以用写文件到磁盘的方式来保存持久化数据。

 

-         (void)applicationDidFinishLaunching:(UIApplication *)application{
 
 NSString *strOne = @"Persistent data1";
 NSString *strTwo = @"Persistent data 2";
 
 NSMutableArray *persistentArray =[[NSMutableArray alloc] init];
 [persistentArray addObject:strOne];
 [persistentArray addObject:strTwo];
 
 
 
 NSArray *filePathArray =NSSearchPathForDirectoriesInDomains(NSDocumentDirectory,NSUserDomainMask, YES);
 NSString *filePath =

-         [[filePathArray objectAtIndex:0]stringByAppendingPathComponent:@"mydatas.plist"];
 
 [[NSArray arrayWithObjects:persistentArray,nil]writeToFile:filePath atomically:NO];
 
 //load
 NSMutableArray *saveDataArray = [[NSMutableArrayalloc] init];
 if([[NSFileManager defaultManager]fileExistsAtPath:filePath])
  saveDataArray = [NSMutableArrayarrayWithContentsOfFile:filePath]; 
 else
  saveDataArray = [NSMutableArrayarrayWithContentsOfFile:[[NSBundle

-                 mainBundle] pathForResource:@"Savedatas" ofType:@"plist"]];

-         
 NSArray *strArray = [saveDataArrayobjectAtIndex:0];
 
 NSString *UnstrOne = [strArrayobjectAtIndex:0];
 NSString *UnstrTwo = [strArrayobjectAtIndex:1];

 // Overridepoint for customization after application launch
 [window makeKeyAndVisible];