深入理解iPhone数据持久化(手把手教你iphone开发 – 基础篇)
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。
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- (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:
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- (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] 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:
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(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.
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->Existing Files…”,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:
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#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 |
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(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; //创建表 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,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。
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(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]; } |