Create combo box and populate items dynamically

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I have a combo box (cboTable) that contains list of database tables. When I select a table, it should generate a number of combo boxes that contains table columns name. If the table has 4 columns then 4 combo boxes should be created with each of columns name as the default value of each combo box.

I want to change the current codes so I can create combo boxes and populate its items dynamically. Could someone helps me to do this? Thank you.

C#

private void cboTable_SelectedIndexChanged(object sender, EventArgs e)
    {
        TableID = cboTable.SelectedItem.ToString();
        SqlCommand cmd;
        SqlDataReader dr;

        SqlConnection CS = new SqlConnection();
        CS.ConnectionString = System.Configuration.ConfigurationManager.ConnectionStrings["conel"].ConnectionString;
        cmd = new SqlCommand("select Column_name from Information_schema.columns where Table_name = @TableID");
        CS.Open();
        cmd.Connection = CS;
        cmd.Parameters.AddWithValue("@TableID", cboTable.SelectedItem.ToString());
        dr = cmd.ExecuteReader();
        

        cboON1.Items.Clear();
        cboON2.Items.Clear();
        cboON3.Items.Clear();
        cboON4.Items.Clear();

        while (dr.Read())
        {
            cboON1.Items.Add(dr["Column_name"]);
            cboON2.Items.Add(dr["Column_name"]);
            cboON3.Items.Add(dr["Column_name"]);
            cboON4.Items.Add(dr["Column_name"]);
        }

        cboON1.SelectedIndex = 0;
        cboON2.SelectedIndex = 1;
        cboON3.SelectedIndex = 2;
        cboON4.SelectedIndex = 3;

        CS.Close();

    }

What I have tried:

I created the following codes but it only populate column names in the first combo box while the other comboboxes are empty.

C#

for (int i = 1; i < 5; i++)
                {
                    ComboBox cb = new ComboBox();
                    cb.Location = new Point(475, 25 * i + 210);
                    switch (i)
                    {
                        case 0:
                            cb.Click += new EventHandler(ButtonClick2);
                            break;

                    }

                    this.Controls.Add(cb);
                    while (dr.Read()) 
                    {
                         cb.Items.Add(dr["Column_name"]);
                    }
                    
                }

Posted 1-Oct-20 17:21pm

Daniel Vero

Updated 1-Oct-20 21:47pm

OriginalGriff

v2

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Comments

BillWoodruff 2-Oct-20 0:16am

If there are four DataTables, and you select one of them ... and, you want a second ComboBox to show the Column names of the selected Table: why do you need to show four additional ComboBoxes rather than one ?

Daniel Vero 2-Oct-20 0:20am

Because I need to compare every combo box with the other combo boxes that show the column name from the excel file.

BillWoodruff 2-Oct-20 22:44pm

I am still unclear as to what your intent is here. You select a DataTable in one ComboBox; then, you create new ComboBoxes for each Column in the selected DataTable. You add the column name to the new ComboBoxes.

1. does every DataTable have the same number of Columns ? Always #4 ?

2. then what: what else goes into the newly created ComboBoxes ?

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Maciej Los · Accepted Answer · 2020-10-01T21:47:00

Follow the steps from MSDN: Add controls to Windows forms by Visual C# - C# | Microsoft Docs[^]

[EDIT]

First of all, add this line in the top of Form:

C#

//this is needed for later use
List<ComboBox> comboBoxes  = new List<ComboBox>();

Second, add this procedure:

C#

private void RemoveExistingComboBoxes()
{
    foreach (ComboBox cb in comboBoxes)
        this.Controls.Remove(cb);
    comboBoxes.Clear();
}

Finally, in a cboTable_SelectedIndexChanged event:

C#

DataTable dt = new DataTable();
string tid = cboTable.SelectedItem.ToString();
string connString  = CS.ConnectionString = ConfigurationManager.ConnectionStrings["conel"].ConnectionString;

using(SqlConnection CS = new SqlConnection(connString))
	using(SqlCommand cmd = new SqlCommand("select Column_name from Information_schema.columns where Table_name = @TableID", CS))
	{
		CS.Open();
	    cmd.Parameters.AddWithValue("@TableID", tid);
		using(SqlDataReader reader = cmd.ExecuteReader())
			dt.Load(reader);
	}
RemoveExistingComboBoxes();
for(int i = 0; i<dt.Rows.Count; i++)
{
	
	ComboBox cb = new ComboBox();
	//populate other properties here
	cb.Parent = this;
	comboBoxes.Add(cb);
}

That's all. Good luck!