iOS - 从 UIAlertView 添加数据到 sqlite

Question

我想询问用户是否想将他在游戏中的分数添加到高分中，并且在输入中我想询问他的名字。他完成后我有这样的代码:

ListOfScores *listOfScores =[[ListOfScores alloc] init];
        if ([listOfScores GetScoresCount] < 10) {
            [self ShowMessageBoxForHighScore];
        }
        else if([listOfScores GetLastScore] < self.ActualScore)
        {
            [self ShowMessageBoxForHighScore];
        }

- (void)ShowMessageBoxForHighScore
{
    UIAlertView *alert = [[UIAlertView alloc] initWithTitle:@"save score" message:@"input username:" delegate:self cancelButtonTitle:@"cancel" otherButtonTitles:nil];

    alert.alertViewStyle = UIAlertViewStylePlainTextInput;
    alert.tag = 12;

    [alert addButtonWithTitle:@"save"];
    [alert show];
}

- (void)alertView:(UIAlertView *)alertView didDismissWithButtonIndex:(NSInteger)buttonIndex
{
    if (alertView.tag == 12) {
        if (buttonIndex == 1) {
            UITextField *textfield = [alertView textFieldAtIndex:0];
            ListOfScores *listOfScores =[[ListOfScores alloc] init];
            Score* score = [[Score alloc] initWithName:textfield.text Points:self.ActualScore];
            [listOfScores AddScore:score];
        }
    }
}

这些是我检查和创建数据库的方法:

-(BOOL)CreateTableForScores {
    BOOL ret;
    int rc;
    // SQL to create new table

    NSString *sql_str = @"CREATE TABLE Scores (pk INTEGER PRIMARY KEY  AUTOINCREMENT  NOT NULL , Points INTEGER DEFAULT 0, Name VARCHAR(100))";

    const char *sqlStatement = (char *)[sql_str UTF8String];
    NSLog(@"query %s",sqlStatement);

    sqlite3_stmt *stmt;
    rc = sqlite3_prepare_v2(db, sqlStatement, -1, &stmt, NULL);

    ret = (rc == SQLITE_OK);
    if (ret)
    { // statement built, execute
        rc = sqlite3_step(stmt);
        ret = (rc == SQLITE_DONE);
    }

    sqlite3_finalize(stmt); // free statement
    NSLog(@"creating table");
    return ret;
}

-(BOOL)TableForScoresExists {
    sqlite3_stmt *statementChk;
    sqlite3_prepare_v2(db, "SELECT name FROM sqlite_master WHERE type='table' AND name='Scores';", -1, &statementChk, nil);

    bool boo = FALSE;

    if (sqlite3_step(statementChk) == SQLITE_ROW) {
        boo = TRUE;
    }
    sqlite3_finalize(statementChk);

    return boo;
}

和我的 AddScore 方法:

- (void) AddScore:(Score *)newScore
{
    @try {
        BOOL tableExists = self.TableForScoresExists;
        if(!tableExists)
        {
            tableExists = self.CreateTableForScores;
        }

        if(tableExists)
        {
                NSString *filename = @"database.sqlite";
                NSFileManager *fileManager = [NSFileManager defaultManager];
                NSString *bundlePath       = [[[NSBundle mainBundle] resourcePath ]stringByAppendingPathComponent:filename];
                NSString *documentsFolder  = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES)[0];
                NSString *documentsPath    = [documentsFolder stringByAppendingPathComponent:filename];
                //NSString *dbPath = [[[NSBundle mainBundle] resourcePath ]stringByAppendingPathComponent:@"Milionar.sqlite"];
                const char *sql = "INSERT INTO Scores(Points,Name) VALUES(?,?)";


                if (![fileManager fileExistsAtPath:documentsPath])
                {
                    BOOL success;
                    NSError *error = nil;
                    success = [fileManager copyItemAtPath:bundlePath toPath:documentsPath error:&error];
                    NSAssert(success, @"Unable to copy database: %@", error);
                }

                if(sqlite3_open([documentsPath UTF8String], &db) == SQLITE_OK)
                {
                    sqlite3_stmt *sqlStatement;
                    if(sqlite3_prepare_v2(db, sql, -1, &sqlStatement, NULL) == SQLITE_OK)
                    {
                        sqlite3_bind_int(sqlStatement, 1, newScore.Points); //
                        sqlite3_bind_text(sqlStatement, 2, [newScore.Name UTF8String], -1, SQLITE_TRANSIENT); //

                        if (sqlite3_step(sqlStatement) != SQLITE_DONE)
                        {
                            NSLog(@"Error while updating. '%s'", sqlite3_errmsg(db));
                        }
                        sqlite3_finalize(sqlStatement);

                    }
                    else
                    {
                        NSLog(@"Problem with prepare statement");
                    }
                }
                else
                {
                    NSLog(@"An error has occured while opening database.");
                }

                sqlite3_close(db);

        }

    }
    @catch (NSException *exception) {
        NSLog(@"An exception occured: %@", [exception reason]);
    }

}

问题是在 AddScore 方法中，当我尝试检查数据库是否存在时，我得到了 false。但是当我不使用 UIAlertView 并且我用一些文本替换 AddScore 的调用警报时，我得到了一切正常并且我保存了 Score 对象。哪里有问题？为什么它在委托(delegate)方法中不起作用？谢谢

Answer 1

CreateTableForScores 和 TableForScoresExists 都需要一个有效的数据库指针。

因此您需要先打开数据库，然后再调用这两个属性中的任何一个。

在您当前的代码片段中，可能会使用未初始化的数据库指针调用这两个函数。

此外，如果您使用“CREATE TABLE IF NOT EXISTS”(https://www.sqlite.org/lang_createtable.html)，则不一定需要调用方法 TableForScoresExists这为您节省了一些代码。