Create a new Windows Form.

Add a GroupBox control with the text property set to Click on a Letter.

Now you will be creating buttons that you will place within the GroupBox control you just created. The buttons will have their property set as listed in Table 3.6.

Table 3.6. Buttons Property Settings

Object	Property	Setting
Button	Name	btnA
	Caption	A
Button	Name	btnB
	Caption	B
Button	Name	btnC
	Caption	C
...
Button	Name	btnZ
	Caption	Z
Button	Name	btnAll
	Caption	All

Add the DataGrid, the Label, and the ComboBox controls shown in Listing 3.6.

Table 3.7. DataGrid, Label, and ComboBox Controls Property Settings

Object	Property	Setting
DataGrid	Name	dgCustomers
Label	Name	Label1
Label	Caption	Column to Sort On:
ComboBox	Name	cboSortColumns

In the class module for the form, add the following three Private declarations just below the line of code that reads Windows Form Designer generated code. These three objects will be used throughout the form.

Private modaCust As OleDb.OleDbDataAdapter
Private mdtCust As DataTable = New DataTable()
Private mdvCust As DataView = New DataView()

Add the following code to the Load event of the form as shown in Listing 3.6. This code starts out by setting up the modaCust data adapter to grab all the customers to fill the data table called mdtCust. Note that at this point, the data grid has not been filled.

The next task is to load cboSortColumns with the column headings by iterating through each of the data columns in mdtCust and adding them to the Items collection in cboSortColumns. Last, the SetDataViewFilter routine is called. This routine is discussed in step 8.

Listing 3.6 frmHowTo3_4.vb: Loading the Data Table to Be Used in the Form, and Adding Column Names to a ComboBox Control

Private Sub frmHowTo3_4_Load(ByVal sender As Object, _
                    ByVal e As System.EventArgs) Handles MyBase.Load

        Dim strSQL As String
        Dim dcCurr As DataColumn

        '-- Set up the exception catch
        Try

            '-- Create the data adapter and fill the data table
            modaCust = New _
                  OleDb.OleDbDataAdapter("Select * From Customers", _
                  (BuildCnnStr("(local)", "Northwind")))
            modaCust.Fill(mdtCust)

            '-- Load the column names into the sort ComboBox control
            For Each dcCurr In mdtCust.Columns
                Me.cboSortColumns.Items.Add(dcCurr.ColumnName)
            Next

        SetDataViewFilter("B")

        Catch oexpData As OleDb.OleDbException
            MsgBox(oexpData.Message)
        End Try

    End Sub

For each of the command buttons that has a single letter, add the first subroutine displayed here in Listing 3.7 to each of its Click events. For the btnAll Button control, add the second subroutine to the Click event. Each Button control will pass the letter that it represents to the subroutine called SetDataViewFilter, discussed in the next step. The btnAll code simply passes the empty string.

Listing 3.7 frmHowTo3_4.vb: Click Events for Each of the Button Controls

Private Sub btnA_Click(ByVal sender As System.Object, _
                ByVal e As System.EventArgs) Handles btnA.Click
        SetDataViewFilter("A")
End Sub
Private Sub btnAll_Click(ByVal sender As System.Object, _
 ByVal e As System.EventArgs) Handles btnAll.Click
        SetDataViewFilter("")
End Sub

Add the subroutine that is found in Listing 3.8 to the class module of the form. This routine takes the letter value that is passed in strFilterLetter as a parameter. The first task to perform is assigning the DefaultView of the mdtCust DataTable object to the mdvCust data view. Next, the RowFilter property of mdvCust is set to compare the CompanyName column with the Like expression using the strFilterLetter and the % (wildcard). Note that if "" is passed to strFilterLetter, all the records will be listed. Finally, mdvCust is set as the DataSource for dgCustomers, which is the DataGrid control.

Listing 3.8 frmHowTo3_4.vb: Setting the RowFilter Property for a DataView Object

Sub SetDataViewFilter(ByVal strFilterLetter As String)

        mdvCust = mdtCust.DefaultView
        mdvCust.RowFilter = "CompanyName Like '" & strFilterLetter & "%'"
        dgCustomers.DataSource = mdvCust

    End Sub

Add the piece of code that is shown in Listing 3.9 to the SelectdIndexChanged event of the cboSortColumns ComboBox control. This routine compares the current setting of mdvCust's Sort property to the current column name chosen in cboSortColumns. If the two are the same, then the column name is assigned to the Sort property with the DESC keyword added on. If not, then the name of the column is assigned to the Sort property.

Listing 3.9 frmHowTo3_4.vb: Specifying a Column on Which to Sort

Private Sub cboSortColumns_SelectedIndexChanged(ByVal sender As System.Object,
                ByVal e As System.EventArgs) _
                  Handles cboSortColumns.SelectedIndexChanged

        '-- Check to see if the column is currently the sorted field.
        '   If it is, sort on the column in descending order.
        '   Otherwise, set the sort to the name of column.

        If mdvCust.Sort = Me.cboSortColumns.Text Then
            mdvCust.Sort = Me.cboSortColumns.Text & " DESC"
        Else
            mdvCust.Sort = Me.cboSortColumns.Text
        End If

    End Sub