组合框选择更改错误 [英] combobox select change error

问题描述

亲爱的所有人，

我要创建一个选择列表项，当我选择黄金项然后在列表中仅显示金项时，当我选择银项然后在列表框中显示唯一的银项时.

我正在使用以下代码，但出现错误将nvarchar值"Gold"转换为数据类型int时转换失败."那么我的代码有什么问题.

Dear All,

I want to create a selection list item when I am select the gold item then show only gold item in the list and when I m select the silver item then it show the only silver item in the list box.

I am using following code but it gives a error "conversion faild when converting the nvarchar value ‘Gold’ to data type int." so what is the problem in my code.

private void cmboItemType()    //for combobox
{
    string connstr = @"Server=.\SQLEXPRESS ;Initial Catalog=RPSJDB;Integrated Security=True; Max Pool Size=100";
    SqlConnection conn = new SqlConnection(connstr);

    SqlCommand cmd = new SqlCommand("SELECT * FROM ItemTable", conn);
    conn.Open();
    SqlDataReader sdr = cmd.ExecuteReader();
    ArrayList ItemStore = new ArrayList();

    while (sdr.Read())
    {
        ItemStore.Add(new AddValue(sdr.GetString(1), sdr.GetInt32(0)));
    }
    sdr.Close();
    conn.Close();
    cmbItemType.DataSource = ItemStore;
    cmbItemType.DisplayMember = "Display";
    cmbItemType.ValueMember = "Value";
    ItemHaveBeenAdded = true;
}
private void lstboxItem()    //for listbox
{
    string connstr = @"Server=.\SQLEXPRESS ;Initial Catalog=RPSJDB;Integrated Security=True; Max Pool Size=100";
    SqlConnection conn = new SqlConnection(connstr);

    this.lstbItem.Items.Clear();
    SqlCommand cmd = new SqlCommand
        ("SELECT * FROM  ItemTable Where cmbItemType =" + cmbItemType.SelectedValue, conn);

    conn.Open();
    SqlDataReader sdrItem = cmd.ExecuteReader();
    while (sdrItem.Read())
    {
        this.lstbItem.Items.Add(sdrItem.GetString(1));
    }
    sdrItem.Close();
    conn.Close();
}
private void cmbItemType_SelectedIndexChanged(object sender, EventArgs e)
{
      if (this.ItemHaveBeenAdded)
        lstboxItem();
}
public class AddValue
{
    private string Displaym;
    private long Valm;
    public AddValue(string Display, long Value)
    {
        Displaym = Display;
        Valm = Value;
    }
    public string Display
    {
        get { return Displaym; }
    }
    public long Value
    {
        get { return Valm; }
    }
}

推荐答案

避免使用如下代码:

sdr.GetString(1), sdr.GetInt32(0)

用于使用数据读取器读取的数据，因此很难维护.如果您在近期或将来对列顺序进行了任何更改，则还需要更新sdr.GetString(###)和类似结构中使用的所有索引.
可以使用SELECT子句中的显式列名(和顺序)来缓解这种情况.
尝试使用

for using the data read by the datareader, it is hard to maintain. If you make any change in column ordering at any near/far future you will also need to update all the indexes used in sdr.GetString(###) and similar constructs.
This can be mitigated using explicit column names (and ordering) in the SELECT clause.

Try using

myInt32Data = (Int32)srd["put here the name of the column"]

(此处仅以Int32为例).这也将有助于调试查询结果.

(Int32 is just used as an example here). This will also help debugging query results.

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