深入理解iPhone數據持久化(手把手教你iphone開發 - 基礎篇)

原文地址: http://blog.csdn.net/dongfengsun/article/details/4799249

在所有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中可以保存在相應的磁盤目錄中和數據庫中。symbian中因爲權限認證的原因，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可以分爲三大部分：屬性列表、對象歸檔、嵌入式數據庫(SQLite3)、其他方法。

一、屬性列表NSUserDefaults

NSUserDefaults類的使用和NSKeyedArchiver有很多類似之處，但是查看NSUserDefaults的定義可以看出，NSUserDefaults直接繼承自NSObject而NSKeyedArchiver 繼承自NSCoder。這意味着NSKeyedArchiver實際上是個歸檔持久化的類，也就可以使用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];
}

二、對象歸檔NSKeyedArchiver和NSKeyedUnarchiver

iPhone和symbian 3rd一樣，會爲每一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作爲目錄名，在每一次應用程序啓動時，這個字母數字串都是不同於上一次的，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如下圖：

通常使用Documents目錄進行數據持久化的保存，而這個Documents目錄可以通過NSSearchPathForDirectoriesInDomains(NSDocumentDirectory,NSUserdomainMask,YES)得到，代碼如下：

- (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(@"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可以獲取到目錄數爲1，其餘的皆爲0，打印出來的結果如下：

[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] 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.

從打印的結果如下，每次應用程序啓動時生成的數字字母串目錄名字並不一樣。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。

下面需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，數據的尺寸並不是固定的，這個時候就需要使用NSMutalbeArray動態的保存數據，代碼優化如下：

-          (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(@"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] 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.

從上面的圖中可以看到，目錄中還有個tmp目錄，讀者也可以把數據保存在tmp目錄中，獲取這個目錄使用NSTemporaryDirectory()方法。

三、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，本質上來說，數據庫持久化操作是基於文件持久化基礎之上的。
要使用嵌入式數據庫SQLite3，首先需要加載其動態庫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。

首先在頭文件中做如下修改：

#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);
 
 // 如果找到了數據庫文件
 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;

 

//創建表
 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，我們使用
NSFileManager *fileManager = [NSFileManager defaultManager];
BOOL findFile = [fileManager fileExistsAtPath:paths];
來判斷數據庫文件是否已經存在，其實在大多數情況下是沒有必要的，sqlite3_open()方法會自動幫我們判斷數據庫文件是否存在，如果不存在則創建心的數據庫文件。

四、其它方法

除了上面的三種方法來保存持久化數據以外，我們還可以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];
}