Question

也许我是盲目的但是我无法弄清楚我做错了什么。

在2次运行后（数据库中只有2个值），我得到2个不同的值，就像它应该的那样。然后我把它写入NSMutableArray。

但是只有第二个值两次。它不应该添加到数组的末尾吗？我做错了什么？

- (NSMutableArray *)getItemsFromDatabaseWithName:(NSString *)databaseName fromTable:(NSString *)tableName andConstraint:(NSString *)constraint
{
    NSString *absolutePath = [[NSBundle mainBundle].resourcePath stringByAppendingPathComponent:databaseName];
    NSLog(@"%@", absolutePath);

    //Datenbank öffnen --- "**" bedeuten "&" verwenden
    sqlite3_open([absolutePath UTF8String], &_database);

    //check if there is a constraint and if not take 2nd statement
    if (![constraint isEqualToString:@""])
    {
        _statement = [NSString stringWithFormat:@"select * from %@ where %@",tableName, constraint];
    }
    else
    {
        _statement = [NSString stringWithFormat:@"select * from %@",tableName];
    }

    const char *charStatement = [_statement cStringUsingEncoding:NSUTF8StringEncoding];
    sqlite3_stmt *results;
    //new array to return values
    _mutableItemArray = [NSMutableArray new];
    //new ItemModel
    ItemModel *tmpItem = [ItemModel new];

    if (sqlite3_prepare_v2(_database, charStatement, -1, &results, NULL)== SQLITE_OK)
    {
        while (sqlite3_step(results) == SQLITE_ROW)
        {

            _charItemName =  (char *)sqlite3_column_text(results, 1);
            [tmpItem setItemName:[NSString stringWithUTF8String:_charItemName]];

            _charItemDescription = (char *)sqlite3_column_text(results, 2);
            [tmpItem setItemDescription:[NSString stringWithUTF8String:_charItemDescription]];

            _charItemYear = (char *)sqlite3_column_text(results, 3);
            [tmpItem setItemYear:[_dateFormat dateFromString:[NSString stringWithUTF8String:_charItemYear]]];

            _charItemRecommendedBy = (char *)sqlite3_column_text(results, 4);
            [tmpItem setItemRecommendedBy:[NSString stringWithUTF8String:_charItemRecommendedBy]];

            _charItemImage = (char *)sqlite3_column_text(results, 5);
            [tmpItem setItemImage:[NSString stringWithUTF8String:_charItemImage]];


            [_mutableItemArray addObject:tmpItem];

#warning here I get the 2 items correct
            NSLog(@"ItemName: %@",[tmpItem getItemName]);
            NSLog(@"ItemName: %@",[tmpItem getItemDescription]);
        }
    }
    sqlite3_close(_database);

#warning here I get 2 times the same item ???
    NSLog(@"ItemName: %@",[_mutableItemArray objectAtIndex:0]);
    NSLog(@"ItemName: %@",[_mutableItemArray objectAtIndex:1]);

    return _mutableItemArray;
}

Answer 1

您只需创建一个对象tmpItem。

这将被添加到数组中，并且在下一次运行while循环时，您不是要创建新的tmpItem，而是修改旧的tmpItem并将其添加到数组中。

因此，您将得到一个包含指向同一对象tmpItem的两个指针的数组（具有最新状态）。

解决方案：在while循环中创建{{1}}。

Answer 2

如果你查看代码，你会在while循环中看到你一次又一次地设置同一个对象（tmpItem），这就是为什么你的数组最后更新了同一个对象的值。

现在看一下你在while循环中会注意到的代码，我们正在创建新对象并将其存储在NSArray中。

- (NSMutableArray *)getItemsFromDatabaseWithName:(NSString *)databaseName fromTable:(NSString *)tableName andConstraint:(NSString *)constraint
{
NSString *absolutePath = [[NSBundle mainBundle].resourcePath stringByAppendingPathComponent:databaseName];
NSLog(@"%@", absolutePath);

//Datenbank öffnen --- "**" bedeuten "&" verwenden
sqlite3_open([absolutePath UTF8String], &_database);

//check if there is a constraint and if not take 2nd statement
if (![constraint isEqualToString:@""])
{
    _statement = [NSString stringWithFormat:@"select * from %@ where %@",tableName, constraint];
}
else
{
    _statement = [NSString stringWithFormat:@"select * from %@",tableName];
}

const char *charStatement = [_statement cStringUsingEncoding:NSUTF8StringEncoding];
sqlite3_stmt *results;
//new array to return values
_mutableItemArray = [NSMutableArray new];
//new ItemModel

if (sqlite3_prepare_v2(_database, charStatement, -1, &results, NULL)== SQLITE_OK)
{
    while (sqlite3_step(results) == SQLITE_ROW)
    {
          ItemModel *tmpItem = [ItemModel new];

        _charItemName =  (char *)sqlite3_column_text(results, 1);
        [tmpItem setItemName:[NSString stringWithUTF8String:_charItemName]];

        _charItemDescription = (char *)sqlite3_column_text(results, 2);
        [tmpItem setItemDescription:[NSString stringWithUTF8String:_charItemDescription]];

        _charItemYear = (char *)sqlite3_column_text(results, 3);
        [tmpItem setItemYear:[_dateFormat dateFromString:[NSString stringWithUTF8String:_charItemYear]]];

        _charItemRecommendedBy = (char *)sqlite3_column_text(results, 4);
        [tmpItem setItemRecommendedBy:[NSString stringWithUTF8String:_charItemRecommendedBy]];

        _charItemImage = (char *)sqlite3_column_text(results, 5);
        [tmpItem setItemImage:[NSString stringWithUTF8String:_charItemImage]];


        [_mutableItemArray addObject:tmpItem];

        NSLog(@"ItemName: %@",[tmpItem getItemName]);
        NSLog(@"ItemName: %@",[tmpItem getItemDescription]);
    }
}
sqlite3_close(_database);

NSLog(@"ItemName: %@",[_mutableItemArray objectAtIndex:0]);
NSLog(@"ItemName: %@",[_mutableItemArray objectAtIndex:1]);

return _mutableItemArray;
}

NSMutableArray会覆盖这些值

2 个答案: