VS 2022 C# ComboBox operations using WinForms. Adding data from SQL server and later capturing selected value.

Question

VS 2022 C# ComboBox operations using WinForms. Adding data from SQL server and later capturing selected value.

Ed Januskis 66

I am looking the way to allocate data from SQL server table.

get 2 columns (ProductID (int) and ProductName (string) from database table into ComboBox.
show only product name.
Capture selected value in drop down of comboBox. The trick is to get ProductID not ProductName.
This will be used to query product details in different action method.
NOTE: I can get data into CombBox, but i cannot. capture ProductID. in my code i use “DnameID”

Code:
private void LoadInfo_Load(object sender, EventArgs e)
{
String req = SQL.CmbDrivrList; //getting SQL statment select…form …
try
{
DataSet dsDataFromDB = SQL.GetDataFromDatabase(req); //class getting DB connections and data. No issues here
cmbDriverList.DataSource = dsDataFromDB.Tables[0];
cmbDriverList.SelectedValue = “DnameID”;
cmbDriverList.DisplayMember = “Dname”;
cmbDriverList.DataSource = dsDataFromDB.Tables[0];
}
catch (Exception exc)
{
MessageBox.Show(exc.Message);
}
private void cmbDriverList_SelectedIndexChanged(object sender, EventArgs e)
{
//This is not working i do not know how to assign to txtBox selected Item. This is a test.
tempID.Text = cmbDriverList.SelectedItem.ToString(); //Goal is to capture “DnameID”
}

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Answer 1

Michael Taylor 60,161

You're close but using the wrong properties. DisplayMember indicates the property on your object to use for the display value. ValueMember indicates the property on your object that holds the actual value. Set that to DnameID and see if your problem goes away.

cmdbDriverList.DisplayMember = "Dname";
cmdbDriverList.ValueMember = "DnameID";

Assuming those are names of columns in your table then it should properly bind the data.

Note also that you have 2 calls to set DataSource. Remove one of them, ideally the first one.

Ed Januskis 66 Reputation points

2022-06-03T15:18:59.707+00:00

@Michael Taylor
Thank you for replay.

So how to capture it? TempID.Text = cmbDriverList.ValueMember.ToString(); This command displays 'DnameID' not actual value.
Michael Taylor 60,161 Reputation points

2022-06-03T15:30:08.313+00:00
ValueMember is the name of the property, not the value. It seems like you want the displayed text. In that case use SelectedText.

temID.Text = cmbDriverList.SelectedText;

However other than display you probably shouldn't need it. The underlying row will have the updated dnameID value if the user changes the selection. But the combo won't know that it needs to update the dname as that is just a static display value so it won't set it.

Note that in most cases your row will just contain the ID (and not the name). The combo should be bound separately to the product list from which the row gets its data. You don't seem to be doing that here and that is OK but if you need much more functionality then what you have now then it is something you should consider doing as demoed here.
Ed Januskis 66 Reputation points

2022-06-03T16:14:59.123+00:00
@Michael Taylor

temID.Text = cmbDriverList.SelectedText;

For some reason it returns blank (null) value. Should I add another condition?

Michael Taylor 60,161

Ok, first I thought you wanted the display value, not the actual value. So let's fix that.

temID.Text = cmbDriverList.SelectedValue?.ToString();

This puts the DnameID of the selected item, if any, in the control called temID.

The load code would look like this:

DataSet dsDataFromDB = SQL.GetDataFromDatabase("query");
cmbDriverList.DisplayMember = "Dname";
cmbDriverList.ValueMember = "DnameID";
cmbDriverList.DataSource = dsDataFromDB.Tables[0];

The assumption is that SQL.GetDataFromDatabase returns back a table that looks like this.

public static class SQL
{
    public static DataSet GetDataFromDatabase(string query)
    {
        var ds = new DataSet();

        var dtDrivers = ds.Tables.Add();
        dtDrivers.Columns.AddRange(new[]
        {
            new DataColumn("DnameID", typeof(int)),
            new DataColumn("Dname", typeof(string))
        });

        dtDrivers.Rows.Add(1, "Driver 1");
        dtDrivers.Rows.Add(2, "Driver 2");
        dtDrivers.Rows.Add(3, "Driver 3");
        dtDrivers.Rows.Add(4, "Driver 4");

        return ds;
    }
}

Here I'm just using an in-memory table, your code will pull from the DB but note that the columns need to line up. You should confirm that your DB query is returning the expected data.

Ed Januskis 66

@Michael Taylor

This is my code for DB execution (note me SQL statement is valid and returns only 2 columns with 14 rows Select ID as DnameID, ProductNAME as Dname from..... )

public static DataSet GetDataFromDatabase(string sql)  
{  
    DataSet ds = new DataSet();  
    try  
    {  
        // database Connection String  
        using (SqlConnection sqlCon = new SqlConnection(connectionString:   
            ConfigurationManager.ConnectionStrings["DatabaseConnectionString"].ConnectionString))  
        {  
            using (SqlDataAdapter SqlDa = new SqlDataAdapter(sql, sqlCon))  
            {  
                SqlDa.SelectCommand.CommandType = CommandType.Text;  
                SqlDa.Fill(ds);  
            }  
        }  
        return ds;  
    }  
    catch (Exception)  
    {  
        throw;  
    }

Michael Taylor 60,161 Reputation points

2022-06-03T18:00:22.837+00:00

That's boilerplate SQL code and doesn't really help with the actual problem you were having since the SQL statement is passed into the function. Nevertheless did you try my updated code for setting the control's Text property and verify it worked correctly? If it doesn't then either the control is empty or it generates an error. Please clarify the behavior you're seeing now because given a valid SQL query that returns data like I described then it should work just fine.

If it isn't then set a breakpoint on the selection changed event handler and check the data to see if it lines up with what I said it should be.
Ed Januskis 66 Reputation points

2022-06-03T18:07:55.213+00:00

@Michael Taylor
Oh.. I missed you update with:

temID.Text = cmbDriverList.SelectedValue?.ToString();

And this worked! Thank you so much!
-Ed

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VS 2022 C# ComboBox operations using WinForms. Adding data from SQL server and later capturing selected value.

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