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我无法从我的sqlite数据库中检索数据。数据存在于其中（我通过手动打开我的数据库文件来检查它）。与数据库的连接已成功建立。我的 sqlite3_step 语句也返回 SQLITE_OK。但结果集不包含任何内容。！这是代码片段：

 - (void)viewDidLoad
    {
        [super viewDidLoad];

        databaseReferences = [[DatabaseReferences alloc]init];

        const char *newPath = [databasepath UTF8String];
        int opened = sqlite3_open(newPath, &db);

        if(opened == SQLITE_OK)
        {
            NSLog(@"Database for processing login query opened successfully...");
        }
        else
        {
            NSLog(@"Database for processing login query NOT OPENED...");
        }
    }

注意：这里的 databaseReferences 是一个包含sqlite3类型变量的类的对象

实际上，在 UI 端，用户输入用户名和密码，我将用户输入的字段与我的 sqlite 数据库中已经存在的数据进行匹配。当用户按下登录按钮时。发生以下情况：

-(BOOL)processLoginQueryusername:(NSString *)uname password:(NSString *)pwd
{
    const char *getUsernames = "select Username from LoginTable";
    int outcome = sqlite3_prepare_v2(db, getUsernames, -1, &statement, NULL);

    if(outcome != SQLITE_OK)
    {
        NSLog(@"could not find the usernames");
        NSLog(@"the error is %s", sqlite3_errmsg(db));
    }

    else
    {
        NSLog(@"got the usernames.. Now checking for valid username and password entry..");

        NSLog(@"the number of columns returned is %d", sqlite3_column_count(statement));

        int i = 0;
        while( sqlite3_step(statement)== SQLITE_ROW)
        {
            NSString *name = [NSString stringWithUTF8String:(const char *)sqlite3_column_text(statement, 0)];
            [usernameList addObject:name];
            NSLog(@"the Username list array contains %d names", usernameList.count);
            NSLog(@"the name is %@", [usernameList objectAtIndex:i]);
            i++;
        }

        for(int i = 0; i<usernameList.count; i++)
        {   
            if([uname isEqualToString:[usernameList objectAtIndex:i]])
            {
                NSLog(@"You are an authenticated user..");
                return YES;
            }
        }
        return NO;
    }

    return NO;
}

这是我的 AppDelegate 方法的代码：

- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions
{
    referenceToDatabase = [[DatabaseReferences alloc]init];
    [referenceToDatabase establishDatabaseConnection];
    [referenceToDatabase release];
    //code for initializing window.. so not including that code
}

referenceToDatabase是包含 sqlite3 变量的类的对象。这是我调用的方法：

-(BOOL)establishDatabaseConnection
{
    usernameList = [[NSMutableArray alloc] init];

    NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);
    NSString *dbPath = [paths objectAtIndex:0];
    databaseName = @"TaskManagementDatabase.sql";

    databasepath = [dbPath stringByAppendingPathComponent:databaseName];
    NSLog(@"%@",databasepath);

    NSFileManager *fileManager = [NSFileManager defaultManager];

    if([fileManager fileExistsAtPath:databasepath])
    {
        NSLog(@"the database already exists");
        return YES;
    }

    else
    {
        NSLog(@"database does not exist.. creating the database");
        const char *newPath = [databasepath UTF8String];
        int opened = sqlite3_open(newPath, &db);

        if(opened == SQLITE_OK)
        {
            NSLog(@"newly created database opened successfully...");
            [self createBothTables];
            [self insertInitialDataIntoBothTables];
            sqlite3_close(db);
            return YES;
        }

这就是我在控制台上得到的：

TaskListManagementApplication[9838:c07] 得到了用户名.. 现在检查有效的用户名和密码条目.. 2013-09-02 11:33:55.134 TaskListManagementApplication[9838:c07] 返回的列数是 1 2013-09-02 11 :33:55.135 TaskListManagementApplication[9838:c07] 用户名列表数组包含 0 个名称 2013-09-02 11:33:55.136 TaskListManagementApplication[9838:c07] 名称为 (null) 2013-09-02 11:33:55.136 TaskListManagementApplication [9838:c07] 用户名列表数组包含 0 个名称 2013-09-02 11:33:55.136 TaskListManagementApplication[9838:c07] 名称为 (null) 2013-09-02 11:33:55.137 TaskListManagementApplication[9838:c07]用户名列表数组包含 0 个名称 2013-09-02 11:33:55.137 TaskListManagementApplication[9838:c07] 名称为 (null) 2013-09-02 11:33:55.137 TaskListManagementApplication[9838:c07] 用户名列表数组包含 0 个名称 2013-09-02 11:33:55.138 TaskListManagementApplication[9838:c07] 名称为 (null) 2013-09-02 11:33:55.138 TaskListManagementApplication[9838:c07] 用户名列表数组包含 0 个名称 2013-09-02 11:33:55.138 TaskListManagementApplication[9838:c07] 名称为 (null)

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