现在ios里使用的数据库一般都是Sqlite，但是使用Sqlite有个不太好的地方就是在多线程的时候，会出现问题，sqlite只能打开一个读或者写连结。这样的话多线程就会碰到资源占用的问题。
最开始是使用FMDB，FMDB的早期版本不能解决这个问题，后来FMDB更新了，新版本的FMDB能够很好的解决这个多线程使用Sqlite 。
FMDB github网址 https://github.com/ccgus/fmdb 最新版的请到github取下载。
本文演示了使用FMDB通过多线程来读和写数据库操作。
1.建立数据库表，我采用的是Firefox的Sqlite manager 来建立的。
建表sql如下
CREATE TABLE "tbl_user" ("_id" INTEGER PRIMARY KEY AUTOINCREMENT NOT NULL , "name" VARCHAR(30), "password" VARCHAR(30))
2. 建立数据表的映射实体UserEntity
#import <Foundation/Foundation.h> @interface UserEntity : NSObject { int _id; NSString *name; NSString *password; } @property (nonatomic, assign) int ID; @property (nonatomic, retain) NSString *name; @property (nonatomic, retain) NSString *password;
@end
3. 建立操作数据库的dao
// // DbDao.m // SqliteTest // // Created by foxwang on 12-4-9. // Copyright (c) 2012年 __MyCompanyName__. All rights reserved. // #import " DbDao.h " #import " DbFileManager.h " #import " FMDatabase.h " #import " FMDatabaseAdditions.h " #import " FMDatabasePool.h " #import " FMDatabaseQueue.h " #import " UserEntity.h " static DbDao *gSharedInstance = nil; @implementation DbDao @synthesize dbFile; @synthesize dbQueue; +(DbDao *)sharedInstance { @synchronized(self) { if (gSharedInstance == nil) gSharedInstance = [[DbDao alloc] init]; } return gSharedInstance; } - ( void)dealloc { [self.dbFile release]; self.dbQueue = nil; [super dealloc]; } - ( id)init { self = [super init]; if (self) { self.dbFile = [DbFileManager dbFilePath]; self.dbQueue = [FMDatabaseQueue databaseQueueWithPath:self.dbFile]; } return self; } - (UserEntity *)rsToUser:(FMResultSet*)rs { UserEntity *user = [[[UserEntity alloc] init] autorelease]; user.ID = [rs intForColumn: @" _id "]; user.name = [rs stringForColumn: @" name "]; user.password = [rs stringForColumn: @" password "]; return user; } - ( void)addUser:(UserEntity *)user { [self.dbQueue inTransaction:^(FMDatabase *db, BOOL *rollback) { [db open]; NSString *sql = @" insert into tbl_user(name, password) values (?, ?) "; [db executeUpdate:sql,user.name, user.password]; [db close]; }]; } - (NSArray *)getUsers; { __block NSMutableArray *users = [[[NSMutableArray alloc] init] autorelease]; [self.dbQueue inDatabase:^(FMDatabase *db) { [db open]; NSString *sql = @" select * from tbl_user "; FMResultSet *rs = [db executeQuery:sql]; while ([rs next]) { [users addObject:[self rsToUser :rs]]; } [db close]; }]; return users; }
@end
4. 编写测试方法
在didFinishLaunchingWithOptions 方法里启动3个线程 ：2个线程写，1个线程读
- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions
{ self.window = [[[UIWindow alloc] initWithFrame:[[UIScreen mainScreen] bounds]] autorelease]; // Override point for customization after application launch. self.viewController = [[[ViewController alloc] initWithNibName: @" ViewController " bundle:nil] autorelease]; self.window.rootViewController = self.viewController; [self.window makeKeyAndVisible]; [NSThread detachNewThreadSelector:@selector(writeDbOne) toTarget:self withObject:nil]; [NSThread detachNewThreadSelector:@selector(readDb) toTarget:self withObject:nil]; [NSThread detachNewThreadSelector:@selector(writeDbTwo) toTarget:self withObject:nil]; return YES; }
- ( void)writeDbOne { DbDao *dao = [DbDao sharedInstance]; for ( int i = 0; i < 500; i++) { @autoreleasepool { UserEntity *user = [[[UserEntity alloc] init] autorelease]; user.name = [NSString stringWithFormat: @" name %d ", i]; user.password = [NSString stringWithFormat: @" password %d ", i]; [dao addUser:user]; NSLog( @" writeDbOne %d ", i); } } } - ( void)writeDbTwo { DbDao *dao = [DbDao sharedInstance]; for ( int i = 600; i < 1200; i++) { @autoreleasepool { UserEntity *user = [[[UserEntity alloc] init] autorelease]; user.name = [NSString stringWithFormat: @" name %d ", i]; user.password = [NSString stringWithFormat: @" password %d ", i]; [dao addUser:user]; NSLog( @" writeDbTwo %d ", i); } } } - ( void)readDb { DbDao *dao = [DbDao sharedInstance]; NSArray *users = [dao getUsers]; NSLog( @" %@ ", users);
}
最后查看数据库信息，数据成功插入
结论 ：使用新的FMDB ，很好的解决了多线程问题。
团结就是力量,ios开发者自己的推广联盟 QQ群173063969