Bind Data to ComboBox and DataGrid Controls

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1,8 Bind dữ liệu vào ComboBox và DataGrid Controls Đôi khi bạn có thể muốn sử dụng điều khiển ComboBox thay vì một điều khiển ListBox để hiển thị một danh sách các lựa chọn. Bạn cũng có thể muốn hiển thị thông tin trong một phong cách lưới dựa trên các mục chọn trong hộp kết hợp. d kỹ thuật mã hóa mà bạn đã sử dụng cho điều khiển ListBox

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Nội dung Text: Bind Data to ComboBox and DataGrid Controls

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.