深刻理解iPhone數據持久化

在全部的移動開發平臺數據持久化都是很重要的部分：在j2me中是rms或保存在應用程序的目錄中，在symbian中能夠保存在相應的磁盤目錄中和數據庫中。symbian中由於權限認證的緣由，在3rd上大多數只能訪問應用程序的private目錄或其它系統共享目錄。在iphone中，apple博採衆長，提供了多種數據持久化的方法，下面筆者會逐個進行詳細的講解。 iphone提供的數據持久化的方法，從數據保存的方式上講能夠分爲三大部分：屬性列表、對象歸檔、嵌入式數據庫(SQLite3)、其餘方法。 1、屬性列表NSUserDefaults NSUserDefaults類的使用和NSKeyedArchiver有不少相似之處，可是查看NSUserDefaults的定義能夠看出，NSUserDefaults直接繼承自NSObject而NSKeyedArchiver 繼承自NSCoder。這意味着NSKeyedArchiver其實是個歸檔持久化的類，也就可使用NSCoder類的［encodeObject: (id)objv forKey:(NSString *)key］方法來對數據進行持久化存儲。   - (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、對象歸檔NSKeyedArchiver和NSKeyedUnarchiver iPhone和symbian 3rd同樣，會爲每個應用程序生成一個私有目錄，這個目錄位於 /Users/sundfsun2009/Library/Application Support/iPhone Simulator/User/Applications下，並隨即生成一個數字字母串做爲目錄名，在每一次應用程序啓動時，這個字母數字串都是不一樣於上一次的，上一次的應用程序目錄信息被轉換成名爲.DS_Store隱藏文件，這個目錄的文件結構以下圖： 一般使用Documents目錄進行數據持久化的保存，而這個Documents目錄能夠經過NSSearchPathForDirectoriesInDomains(NSDocumentDirectory,NSUserdomainMask,YES)獲得，代碼以下： - (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()的第二個參數是個枚舉值，在筆者的測試代碼中，只有NSUserDomainMask和NSAllDomainsMask能夠獲取到目錄數爲1，其他的皆爲0，打印出來的結果以下： [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. 從打印的結果以下，每次應用程序啓動時生成的數字字母串目錄名字並不同。在調用[NSKeyedArchiver archiveRootObject:persistentArray toFile:myFilename]方法前，文件myFile.rtf並每生成，只有在調用此方法後才產生相應的文件。 下面須要把數據從屬性列表中讀取出來，在上面的代碼中，筆者使用NSArray保存數據。但在大多數應用程序中，數據的尺寸並非固定的，這個時候就須要使用NSMutalbeArray動態的保存數據，代碼優化以下： -          (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]; }   輸出結果以下：   [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. 從上面的圖中能夠看到，目錄中還有個tmp目錄，讀者也能夠把數據保存在tmp目錄中，獲取這個目錄使用NSTemporaryDirectory()方法。 3、嵌入式數據庫(SQLite3) 嵌入式數據庫持久化數據就是把數據保存在iphone的嵌入式數據庫系統SQLite3中，本質上來講，數據庫持久化操做是基於文件持久化基礎之上的。 要使用嵌入式數據庫SQLite3，首先須要加載其動態庫libsqlite3.dylib，這個文件位於/Xcode3.1.4/Platforms/iPhoneOS.platform/Developer/SDKs/iPhoneOS3.1.sdk/usr/lib目錄下。在Framework文件夾上右擊，選擇「Adding->Existing Files...」，定位到上述目錄並加載到文件夾。 首先在頭文件中作以下修改： #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);    // 若是找到了數據庫文件  if(findFile)  {   NSLog(@"Database file have already existed.");     if(sqlite3_open([paths UTF8String], &database) != SQLITE_OK)//打開數據庫失敗   {    sqlite3_close(database);    NSAssert(0,@"Failed to open database");   }  }else  {   NSLog(@"Database file does not exsit!");   if(sqlite3_open([paths UTF8String], &database) != SQLITE_OK)//打開數據庫失敗   {    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";//查找表中的數據   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]; } 在上面的代碼中，咱們使用  NSFileManager *fileManager = [NSFileManager defaultManager]; BOOL findFile = [fileManager fileExistsAtPath:paths]; 來判斷數據庫文件是否已經存在，其實在大多數狀況下是沒有必要的，sqlite3_open()方法會自動幫咱們判斷數據庫文件是否存在，若是不存在則建立心的數據庫文件。 4、其它方法 除了上面的三種方法來保存持久化數據之外，咱們還能夠用寫文件到磁盤的方式來保存持久化數據。 -          (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]; }