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UltraLite for MobileVB User's Guide
  Tutorial: An UltraLite Application for PocketPC
    Lesson 3: Write the sample code

Write code for navigation and data manipulation


The following procedure implements data manipulation and navigation.

To open the table

  1. Write code that initializes the table and moves to the first row.

    Add the following code to the Form_Load event, just before the End Sub instruction:

    Set CustomerTable = Connection.GetTable("customer")
    CustomerTable.Open
    CustomerTable.MoveBeforeFirst
    If Err.Number <> ULSQLCode.ulSQLE_NOERROR Then
        MsgBox Err.Description
    End If

    This code assigns the customer table to CustomerTable and opens the table so data can be read or manipulated. The call to MoveBeforeFirst positions the application before the first row of data in the table. This call is not necessarily required because the call to open positions the application before the first row. There are currently no rows in the table.

  2. Create a new function called DisplayCurrentRow and implement it as shown below.

    Private Sub DisplayCurrentRow()
      If CustomerTable.RowCount = 0 Then
        txtFname.Text = ""
        txtLname.Text = ""
        txtCity.Text = ""
        txtPhone.Text = ""
        lblID.Caption = ""
      Else
        lblID.Caption = _
             CustomerTable.Column("Id").StringValue
        txtFname.Text = _
             CustomerTable.Column("Fname").StringValue
        txtLname.Text = _
             CustomerTable.Column("Lname").StringValue
        If CustomerTable.Column ("City").IsNull Then
          txtCity.text =""
        Else
          txtCity.Text = _
          CustomerTable.Column("City").StringValue
        End If
        If CustomerTable.Column("City").IsNull Then
          txtcity.Text = ""
        Else
          txtphone.Text = _
          CustomerTable.Column("Phone").StringValue
        End If
      End If
    End Sub

    If the table has no rows, the application displays empty controls. Otherwise, it displays the values stored in each of the columns of the current row of the database.

  3. Call this function from the Form's Activate function.

    Private Sub Form_Activate()
        DisplayCurrentRow
    End Sub

    This call ensures the fields get updated when the application starts.

    At this stage you may want to run the application to verify that you have entered the code correctly. As there are no rows in the table, the controls are all empty.

To insert rows into the table

  1. Implement the code for the Insert button.

    Add the following procedure to the form:

    Private Sub btnInsert_Click()
        Dim fname As String
        Dim lname As String
        Dim city As String
        Dim phone As String
    
        fname = txtFname.Text
        lname = txtLname.Text
        city = txtCity.Text
        phone = txtPhone.Text
    
        On Error GoTo InsertError
        CustomerTable.InsertBegin
        CustomerTable.Column("Fname").StringValue = _
          fname
        CustomerTable.Column("Lname").StringValue = _
          lname
        If Len(city) > 0 Then
            CustomerTable.Column("City").StringValue = _
          city
        End If
        If Len(phone) > 0 Then
           CustomerTable.Column("Phone").StringValue = _
           phone
        End If
        CustomerTable.Insert
        CustomerTable.MoveLast
        DisplayCurrentRow
        Exit Sub
    
    InsertError:
        MsgBox "Error:  " & CStr(Err.Description)
    End Sub

    The call to InsertBegin puts the application into insert mode and sets all the values in the row to their defaults. For example, the ID column receives the next autoincrement value. The column values are set and then the new row is inserted. Note that if an error occurs during the insert, a message box will display the error number.

  2. Run the application.

    After the initial message box, the form is displayed.

The following procedure implements the code to scroll through the rows and display each.

To move through the rows of the table

  1. Implement the code for the Next and Previous buttons.

    Add the following procedures to the form:

    Private Sub btnNext_Click()
        If Not CustomerTable.MoveNext Then
            CustomerTable.MoveLast
        End If
        DisplayCurrentRow
    End Sub
    Private Sub btnPrevious_Click()
        If Not CustomerTable.MovePrevious Then
            CustomerTable.MoveFirst
        End If
        DisplayCurrentRow
    End Sub
  2. Run the application.

    When the form is first displayed, the controls are empty as the current position is before the first row.

    Click Next and Previous to move through the rows of the table.

The following procedure modifies the data in a row by updating or deleting it.

To update and delete rows in the table

  1. Implement the code for the Update button.

    Add the following procedure to the form:

    Private Sub btnUpdate_Click()
        Dim fname As String
        Dim lname As String
        Dim city As String
        Dim phone As String
    
        fname = txtFname.Text
        lname = txtLname.Text
        city = txtCity.Text
        phone = txtPhone.Text
        On Error GoTo UpdateError
        CustomerTable.UpdateBegin
        CustomerTable.Column("Fname").StringValue = fname
        CustomerTable.Column("Lname").StringValue = lname
        If Len(city) > 0 Then
            CustomerTable.Column("City").StringValue = city
        Else
            CustomerTable.Column("City").SetNull
        End If
        If Len(phone) > 0 Then
           CustomerTable.Column("Phone").StringValue = phone
        End If
        CustomerTable.Update
        DisplayCurrentRow
        Exit Sub
    
    UpdateError:
        MsgBox "Error:  " & CStr(Err.Description)
    End Sub

    The call to UpdateBegin puts the application into update mode. The column values are updated and then the row itself is updated with a call to Update.

  2. Implement the code for the Delete button.

    Add the following procedure to the form:

    Private Sub btnDelete_Click()
        If CustomerTable.RowCount = 0 Then
            Exit Sub
        End If
        CustomerTable.Delete
        CustomerTable.MoveRelative 0
        DisplayCurrentRow
    End Sub

    The call to Delete deletes the current row on which the application is positioned.

  3. Run the application.

    The data manipulation and display portion of the application is now complete.

Note 
You can now run this application as a stand-alone application without SQL Anywhere Studio. To synchronize your UltraLite database with an Adaptive Server Anywhere database, complete the remainder of this lesson.

Contents Index Write code to connect to your database Write code to synchronize