Tài liệu Bind Data to ComboBox and DataGrid Controls doc

1.8 Bind Data to ComboBox and DataGrid Controls
Sometimes you might want to use a ComboBox control instead of a ListBox control to
display a list of choices. You also might want to display information in a grid style based
on the item chosen in that combo box. This How-To describes how to bind data to both
ComboBox and DataGrid controls.
Instead of using a ListBox control to display customers, you would like to use a
ComboBox control to display them. After you choose a customer, you would like to
display information about the orders that belong to that customer. How do you bind data
to the ComboBox and then bind the DataGrid control as well?
Technique
To bind both the ComboBox and the DataGrid controls, you will use the same properties
and coding techniques that you have used for the ListBox control. You will first create
DataAdapter and DataSet controls to which to set the DataSource properties. The
DataAdapter for the DataGrid will include a parameter that will use the value selected in
the ComboBox control.
You will set the DataSource properties of the controls to the DataSet created. That is all
you really have to set for the DataGrid control. For the ComboBox control, you will also
set the ValueMember and DisplayMember properties.
You will then add code to fill the DataSet control to which the DataSource property is set
for the ComboBox control. Finally, you will create a subroutine to store the selected
value in the ComboBox in the DataAdapter that was created for filling the DataSet on
which the DataGrid control is based.
After the user has selected a value in the ComboBox that contains the customers, the
DataGrid control displays the orders for that customer, as can be seen in Figure 1.14.
Figure 1.14. Users can display the header information for customer orders using
these two controls.

Steps
You will be starting with a fresh form.
1. Add a new Windows Form called frmHowTo1_8.
2. Add the OleDbDataAdapter and DataSet controls with the properties set forth in

Table 1.7.
Table 1.7. OleDataAdapter and DataSet Controls
Object Property Setting
OleDataAdapter Name odaCustomerList
SelectCommand OleDbSelectCommand1
CommandText SELECT CustomerID, CompanyName
FROM Customers
DataSet Name dsCustomerList
DataSetName dsCustomerList
OleDataAdapter Name odaOrdersForCustomer
SelectCommand OleDbSelectCommand2
CommandText SELECT OrderID, OrderDate, RequiredDate,
ShippedDate FROM Orders WHERE
(CustomerID = ?) ORDER BY OrderDate
DataSet Name dsOrdersForCustomer
DataSetName dsOrdersForCustomer
3. Tip

You will want to create the OleDbDataAdapter controls using the
Data Adapter Configuration Wizard, and then set the name after
the DataAdapter has been created. You will want to create the
DataSet controls by right-clicking on the appropriate
OleDbDataAdapter and choosing Generate Dataset. If you have
questions about creating these controls, reread How-To 1.1.
Also, remember that when generating the DataSet, VS always
changes the name by adding a 1 on the end and capitalizing the
first letter. You might want to change it to what you really want in
the properties directly.
4. Add the ComboBox and DataGrid controls, as well as the Label for the
ComboBox, setting the properties as shown in Table 1.8.

Table 1.8. Label, ComboBox, and DataGrid Controls Property Settings
Object Property Setting
Label Name Label1
Text "Customers to List Orders For:"
ComboBox Name cboCustomers
DataSource dsCustomerList.Customers
DisplayMember CompanyName
ValueMember CustomerID
DataGrid Name dgOrders
DataSource dgOrdersForCustomer.Orders
5. Add code shown in Listing 1.23 to the Load event of the form. This code fills the
dsCustomerList DataSet control based off the select statement used in the
odaCustomerList OleDbDataAdapter control. After this occurs, the RefreshOrders
subroutine is called, displayed in Listing 1.24.
Listing 1.23 frmHowTo1_8.vb: Filling the Dataset Used by the ComboBox
Control
Private Sub frmHowTo1_8_Load(ByVal sender As Object, _
ByVal e As System.EventArgs) Handles MyBase.Load

Me.odaCustomerList.Fill(Me.dsCustomerList)
RefreshOrders()

End Sub
Listing 1.24 frmHowTo1_8.vb: Filling the Dataset Used by the DataGrid
Control, Based on the Item Selected in the ComboBox Control
Private Sub RefreshOrders()

'- Clear Orders for customer dataset
Me.dsOrdersForCustomer.Clear()

'- Check to see if an item was selected
If Me.cboCustomers.SelectedIndex <> -1 Then

'- Store the selected customer ID into the parameter
' the SQL data adapter
Me.odaOrdersForCustomer.SelectCommand.Parameters(0).Value = _
Me.cboCustomers.SelectedItem(0)

'- Fill the dataset
Me.odaOrdersForCustomer.Fill(Me.dsOrdersForCustomer)

End If

End Sub
6. Add the code in Listing 1.25 to the SelectedIndexChanged event of the
cboCustomers ComboBox controls.
Listing 1.25 frmHowTo1_8.vb: Refreshing the DataGrid Control Based on
Selected Item
Private Sub cboCustomers_SelectedIndexChanged(ByVal sender
As System.Object, ByVal e As System.EventArgs)
Handles cboCustomers.SelectedIndexChanged

RefreshOrders()

End Sub
How It Works
When the form is first loaded or a new item is selected in the ComboBox control, the
DataGrid control is filled with order information for the selected customer.
Comments
As you can see from this How-To, using the ComboBox control and DataGrid controls

are not much tougher than using the ListBox control. The DataGrid control does offer
quite a bit more power to let you create Main/Subform type forms such as invoices. You
will see an example of this in the next How-To. The DataGrid control also lets you edit
data.