Question

我在C＃中有一个事件，它通过上面提到的类文件中包含的oracle存储过程，使用来自不同数据库的相关值来填充类文件（database.cs）中的下拉列表。这是我目前使用的代码：

    ///<summary>
    ///Populates the model dropdownlist with available chrome data associated with 
    ///the year selected
    /// </summary>
    private void PopulateChromeModel()
    {
        //define a counter
        int itemCounter = 1;

        //create a database object
        Database cmake = new Database();

        //call GetChromeMakeByYear to retrieve the available models according to 
        //the year
        DataTable table = cmake.GetChromeMakeByYear(ddlVehicleYear.SelectedItem);

        Trace.Write("populating models");

        //create a flag showing whether an item should be selected.  Preset it to false
        bool selected = false;

        //we may need to select, then later deselect, an item based on the model.
        int selectedItemByModel = 0;

        //preset the current selected code to ""
        string currentSelectedCode = "";

        //define a flag to indicate whether we've already selected an item.  Preset it to false.
        bool hasSelected = false;

        //create a list item for the 0 position
        ListItem firstItem = new ListItem("-- SELECT --", "");

        //first see if there is a currently selected item.  If so, set the current selected model.
        //this is done because we have to clear all of the selected items before adding the new list.
        //but we want to be able to select the model that is already selected.
        if (ddlVehicleModel.SelectedIndex > 0)
        {
            currentSelectedCode = ddlVehicleModel.SelectedValue;
        }

        //clear any items from the list
        ddlVehicleModel.Items.Clear();

        //add the first item
        ddlVehicleModel.Items.Add(firstItem);

        //loop through the table and add items for each row.
        foreach (DataRow row in table.Rows)
        {
            //get this record's chrome id
            string id = row["CHROME_ID"].ToString();

            //get this record's make
            string make = row["CHROME_MAKE"].ToString();

            //set a flag specifying whether the item should be selected based on year
            bool selectBasedOnYear = false;

            if (currentSelectedCode == id)
            {
                selected = true;
            }
            else
            {
                selected = false;
                selectBasedOnYear = false;
            }

            Trace.Write(string.Format("{0}: {1}: {2}: {3}", id, make, selected, selectBasedOnYear));

            //create a new list item for this model
            ListItem newItem = new ListItem(id, make);

            //if we have thrown either selected flag and we have not already selected an item, 
            //mark this option as selected
            if ((selected || selectBasedOnYear) && !hasSelected)
            {
                Trace.Write("-- Either selected or selectedBasedOnYear was true, and hasSelected was false");

                //first make sure the first item is deselected
                firstItem.Selected = false;
                Trace.Write("-- deselected the first item.");

                //next deselect and items that were selected due to year.  This allows the user selected
                //region to override the default model for year.
                if (selectBasedOnYear != null)
                {
                    Trace.Write(string.Format(" -- deselecting item {0}, which was selected due to year", selectBasedOnYear));
                    ddlVehicleMake.Items[selectedItemByModel].Selected = false;
                }

                //select this item
                newItem.Selected = true;
                Trace.Write(" -- selected the current item");

                //only throw the hasSelected flag if this was a user-selected region
                if (selected)
                {
                    hasSelected = true;
                    Trace.Write(" -- set hasSelected to true");
                }

            }

            //add the model to the list
            ddlVehicleMake.Items.Add(newItem);

            itemCounter++;
        }

        //if there's no items selected and we have more than just the default item, 
        //default to the first item
        if (ddlVehicleMake.Items.Count > 0 && !hasSelected && selectedItemByModel == 0)
        {
            ddlVehicleMake.SelectedIndex = 1;
        }
    }

错误发生在以下行：

        //call GetChromeMakeByYear to retrieve the available models according to 
        //the year
        DataTable table = cmake.GetChromeMakeByYear(ddlVehicleYear.SelectedItem);

我已将我的内联评论和摘要包含在内，以帮助您了解此活动的范围。我不太清楚错误的原因是什么。

Answer 1

您需要将值取消装箱为整数。

DataTable table = cmake.GetChromeMakeByYear((int)ddlVehicleYear.SelectedItem);

当从下拉列表中检索项目时，它们将以对象的形式检索，因为您可以在其中存储任何类型的数据。编译器不知道你在列表中指定的项目实际上是一个整数（而不是一个字符串），所以不知道你试图调用什么函数。

有关拆箱和装箱的更多信息，请访问：http://msdn.microsoft.com/en-us/library/yz2be5wk.aspx

Answer 2

试试这个：

DataTable table = cmake.GetChromeMakeByYear((int) ddlVehicleYear.SelectedValue);

'ColConfigSubsystem.Database.GetChromeMakeByYear（int）'的最佳重载方法匹配有一些无效的参数

2 个答案: