深刻理解iPhone数据持久化

在全部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中能够保存在相应的磁盘目录中和数据库中。symbian中由于权限认证的缘由，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能够分为三大部分：属性列表、对象归档、嵌入式数据库(SQLite3)、其余方法。 1、属性列表NSUserDefaults NSUserDefaults类的使用和NSKeyedArchiver有不少相似之处，可是查看NSUserDefaults的定义能够看出，NSUserDefaults直接继承自NSObject而NSKeyedArchiver 继承自NSCoder。这意味着NSKeyedArchiver其实是个归档持久化的类，也就可使用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]; } 2、对象归档NSKeyedArchiver和NSKeyedUnarchiver iPhone和symbian 3rd同样，会为每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做为目录名，在每一次应用程序启动时，这个字母数字串都是不一样于上一次的，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以下图： 一般使用Documents目录进行数据持久化的保存，而这个Documents目录能够经过NSSearchPathForDirectoriesInDomains(NSDocumentDirectory,NSUserdomainMask,YES)获得，代码以下： - (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(@"myfile's 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能够获取到目录数为1，其他的皆为0，打印出来的结果以下： [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] myfile's path is :/Users/sundfsun2009/Library/Application Support/iPhone Simulator/User/Applications/C93DC783-F137-4660-AE5A-08C3E11C774B/Documents/myFile.rtf Terminating in response to SpringBoard's 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] myfile's path is :/Users/sundfsun2009/Library/Application Support/iPhone Simulator/User/Applications/763E6772-E754-452F-8532-80C2CE4466B5/Documents/myFile.rtf Terminating in response to SpringBoard's termination. 从打印的结果以下，每次应用程序启动时生成的数字字母串目录名字并不同。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。 下面须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，数据的尺寸并非固定的，这个时候就须要使用NSMutalbeArray动态的保存数据，代码优化以下： -          (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(@"myfile's 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]; }   输出结果以下：   [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] myfile's path is :/Users/sundfsun2009/Library/Application Support/iPhone Simulator/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. 从上面的图中能够看到，目录中还有个tmp目录，读者也能够把数据保存在tmp目录中，获取这个目录使用NSTemporaryDirectory()方法。 3、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，本质上来讲，数据库持久化操做是基于文件持久化基础之上的。 要使用嵌入式数据库SQLite3，首先须要加载其动态库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->Existing Files...”，定位到上述目录并加载到文件夹。 首先在头文件中作以下修改： #import <UIKit/UIKit.h> #include "sqlite3.h" #define kFileName @"mydb.sql" @interface PersistentExampleAppDelegate : 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 = [NSFileManager defaultManager];  BOOL findFile = [fileManager fileExistsAtPath:paths];    NSLog(@"Database file path = %@",paths);    // 若是找到了数据库文件  if(findFile)  {   NSLog(@"Database file have already existed.");     if(sqlite3_open([paths UTF8String], &database) != SQLITE_OK)//打开数据库失败   {    sqlite3_close(database);    NSAssert(0,@"Failed to open database");   }  }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 open database");   }  }    char *errorMsg;   //建立表  NSString *createSQL = @"create table if not exists fields (row integer primary key, field_data text);";   if(sqlite3_exec(database, [createSQL UTF8String],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,[upDataSQL UTF8String],NULL,NULL,&errorMsg) != SQLITE_OK)   {    sqlite3_close(database);    NSAssert(0,@"Failed to open database");   }  }    //unarchive  NSString *query = @"select row, field_data from fields order by row";//查找表中的数据   sqlite3_stmt *statement;  if(sqlite3_prepare_v2(database, [query UTF8String], -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 after application launch  [window makeKeyAndVisible]; } 在上面的代码中，咱们使用  NSFileManager *fileManager = [NSFileManager defaultManager]; BOOL findFile = [fileManager fileExistsAtPath:paths]; 来判断数据库文件是否已经存在，其实在大多数状况下是没有必要的，sqlite3_open()方法会自动帮咱们判断数据库文件是否存在，若是不存在则建立心的数据库文件。 4、其它方法 除了上面的三种方法来保存持久化数据之外，咱们还能够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 = [[NSMutableArray alloc] init];  if([[NSFileManager defaultManager] fileExistsAtPath:filePath])   saveDataArray = [NSMutableArray arrayWithContentsOfFile:filePath];    else   saveDataArray = [NSMutableArray arrayWithContentsOfFile:[[NSBundle -                  mainBundle] pathForResource:@"Savedatas" ofType:@"plist"]]; -            NSArray *strArray = [saveDataArray objectAtIndex:0];    NSString *UnstrOne = [strArray objectAtIndex:0];  NSString *UnstrTwo = [strArray objectAtIndex:1];  // Override point for customization after application launch  [window makeKeyAndVisible]; }