iphone - iPhone 和 sqlite 查询的问题

Question

当我尝试运行我的程序时出现以下错误。我得到它的任何理由？我已经尝试了几个小时，但我放弃了。谢谢!

错误:

2011-03-08 19:18:29.967 iphoneApp[2561:207] * 由于未捕获的异常“NSInvalidArgumentException”而终止应用程序，原因:“* +[NSString stringWithUTF8String:]: NULL cString'

- (AnswerDTO *)findAnswerById:(NSInteger)primary_key {
    AnswerDTO *dto = [[[AnswerDTO alloc] init] autorelease];

    sqlite3_stmt *statement = nil;
    const char *sql = "SELECT * FROM klb_answers WHERE id = 7;";

    if (sqlite3_prepare_v2(database, sql, -1, &statement, NULL) == SQLITE_OK) { 
        sqlite3_bind_int(statement, 1, primary_key);

        NSInteger answerId = sqlite3_column_int(statement, ANSWER_ID);
        NSInteger answerQuestionId = sqlite3_column_int(statement, ANSWER_QUESTION_ID);
        NSString *answerDescription = [NSString stringWithUTF8String:(char *)sqlite3_column_text(statement, ANSWER_DESCRIPTION)];
        NSString *answerSerialNumber = [NSString stringWithUTF8String:(char *)sqlite3_column_text(statement, ANSWER_SERIAL_NUMBER)];
        NSInteger answerIsCorrect = sqlite3_column_int(statement, ANSWER_IS_CORRECT);

        dto.answerID = answerId;
        dto.questionID = answerQuestionId;
        dto.description = answerDescription;
        dto.serialNumber = answerSerialNumber;

        if (answerIsCorrect == 0) {
            dto.isCorrect = NO;
        } else {
            dto.isCorrect = YES;
        }
    } else {
        NSLog(@"Noe feil med statementet");
    }

    sqlite3_finalize(statement);

    return dto;
}

Answer 1

看起来您并没有“运行”您的查询。你准备好了它并绑定(bind)了你的参数，但你从未运行 sqlite3_step() 来执行查询并获得响应。即使它是单个记录或标量。

因此，您的列函数返回空值。