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.. Technique To bind both the

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

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

Text "Customers to List Orders For:"

DataSource dsCustomerList.Customers

DisplayMember CompanyName

ValueMember CustomerID

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