Question

我的Windows窗体应用程序中有一个comboBox和一个checkListBox，它连接到我的SQL数据库。我得到了绑定数据部分，但我不知道如何在选择comboBox项时在checkListBox中显示数据。假设我的comboBox中有10个与我的SQL数据库绑定的项目，它们位于列名（“应用程序名称”）下，例如excel，word，android，eclipse等....我在表单开始时调用此方法载入。对不起长代码。

以下是applicationComboBox

的代码

private void loadComboBox()
        {
            myConn = new SqlConnection("Server = localhost; Initial Catalog= dbName; Trusted_Connection = True");

            try
            {
                myConn.Open();

                //my table name is Application_Detail
                string query = "select * from Application_Detail";

                myCommand = new SqlCommand(query, myConn);

                //reading the value from the query
                SqlDataReader dr = myCommand.ExecuteReader();

                //Reading all the value one by one
                while (dr.Read())
                {
                    //column is 1 in Application_Detail Data
                   //GetString(1) display the 2nd column of the table
                    string name = dr.GetString(1);

                    //display the application name in column 2 - 
                    applicationComboBox.Items.Add(name);
                }
                myConn.Close();
            }catch(Exception ex)
            {
                MessageBox.Show(ex.Message);
            }
        }

这部分代码的结果是：

 //label Name        //Application Name
  Application Name:                    
                      Excel
                      Word
                      NotePad
                      PowerPoint
                      SubLime
                      Eclipse

在我调用此方法后，我想根据用户在此applicationComboBox中选择的内容显示教师姓名。因此，如果教师1,2,3使用Excel并且用户从comboBox中选择了excel，则checkListBox将显示教师1,2,3，反之亦然。为此，我在comboBox1_SelectedIndexChanged方法调用方法，因为我想在从comboBox中选择项目时显示详细信息。以下是我的代码

private void comboBox1_SelectedIndexChanged(object sender, EventArgs e)
{

    try
    {
          //I check if the comboBox index is at 0, it disable the button. 
            if (applicationComboBox.SelectedIndex == 0)
            {
                exportButton.Enabled = false;
                this.teacherCheckListBox.DataSource = null;
                teacherCheckListBox.Items.Clear();
            }
          //it it is not at 0, 
            else
            {

                exportButton.Enabled = true;
                 //call this method
                fill_checkListBox();

            }
            //teacherCheckListBox

    }
    catch (Exception ex)
    {
        MessageBox.Show(ex.Message);
    }
}

    private void fill_checkListBox()
        {
            myConn = new SqlConnection("Server = localhost; Initial Catalog= dbName; Trusted_Connection = True");

            try
            {
                myConn.Open();

                //for reading purpose, I break down by long statement 
                //In this statement, I left join 3 table (Teacher_Detail,  AppUser_Detail, and Application_Detail table). My AppUser_Detail contains all 3 id (teacherId, applicationId, and AppUserId). I then set filter the table using `where` keyWord to make the applicationId = the comboBox text 

                string query = "SELECT
                                  td.chineseName,
                                  ad.applicationId,
                                  aud.applicationId,
                                  ad.applicationName 
                              FROM[AppUser_Detail] as aud 
                              LEFT JOIN[Teacher_Detail] as td 
                              ON aud.teacherId = td.teacherId

                              LEFT JOIN[Application_Detail] as ad 
                              ON aud.applicationId = ad.applicationId

                              where aud.applicationId = '" + applicationComboBox.Text + "' AND NOT(td.teacherId IS NULL)
";
                myCommand = new SqlCommand(query, myConn);


                //reading the value from the query
                SqlDataReader dr = myCommand.ExecuteReader();

                //Reading all the value one by one
                while (dr.Read())
                {
                    //column is 0 where the teacherName belong in my Teacher_Detail table

                    string name = dr.GetString(0);

                     //I tried to set the text of the checkListBox as the teacherName, but I can't somehow
                    teacherCheckListBox.Text = name;

                }
                myConn.Close();
            }
            catch (Exception ex)
            {
                MessageBox.Show(ex.Message);
            }
        }

当我运行这样的程序时，它说Conversion failed when converting the varchar value "Excel" to data type int.有没有办法解决它？它应该不是问题，因为在我的Application_Detail表中，我的applicationName和我的teacherName的数据类型被设置为nvarchar（50）和applicationId和teacherId = int;

Answer 1

问题出在这条线上，我想：

 where aud.applicationId = '" + applicationComboBox.Text +

基于你的代码，我认为applicationId是一个int，applicationComboBox.Text就是那个文本。

试试这个：

where ad.applicationName = '" + applicationComboBox.Text.Trim() +

试试这个：

if (string.IsNullOrWhiteSpace(teacherCheckListBox.FindString(name))
{
    teacherCheckListBox.Items.Add(name);
}

如何在ComboBox中显示CheckListBox中的项目

1 个答案: