PRB: Masked Edit May Not Show Empty When Bound Field is Null

• Microsoft Visual Basic Professional and Enterprise Editions for Windows, versions 4.0, 5.0

SYMPTOMS

The Masked Edit control may not show an empty value when it is bound to a field in a Microsoft Access table. If you set the Mask Property of the control and the bound field is null, the control will not display an empty mask. Instead, it will show the value from the last non-null field. If the first record displayed has a null field, the control will show an empty mask. However, as soon as the control displays a non-null field it will not display an empty mask for any other empty field. If the Mask Property is not set, null fields will display as empty in the Masked Edit control.

RESOLUTION

To work around this problem, you can change the text property of the Masked Edit control to an empty string when the bound field to contains a null value:

   Private Sub Data1_Reposition()
   
      'Check to see if the record is empty or contains
      'a zero length string.
      'Note: The AllowZeroLength property of the field must be True.
      If IsNull(Data1.Recordset("Phone")) Or _
         Data1.Recordset("Phone") = "" Then
           'Set the Masked Edit Box to an empty string
           'Note: This sets the DataChanged for MaskEdBox1 to True
           MaskEdBox1.Text = "(___) ___-____"
           bFieldNull = True           'The field has no value
       Else
           bFieldNull = False          'The field has a value
       End If
   
       'Set the mask for the control
       MaskEdBox1.Mask = "(###) ###-####"
   
   End Sub
   
   Private Sub Data1_Validate(Action As Integer, Save As Integer)
   
       If MaskEdBox1.DataChanged Then
   
          'Check to see if the Masked Edit Box has an empty string
          'and that the field was empty when you moved to this record
          If MaskEdBox1.Text = "(___) ___-____" And bFieldNull Then
             'If the control has an empty string and the field is null
             'set the DataChanged to False so that you don't
             'update the field
             MaskEdBox1.DataChanged = False
   
          'If the control now has an empty string but the field
          'had a value when moved to this record you want to remove
          'the value from the field
          ElseIf MaskEdBox1.Text = "(___) ___-____" _
          And Not bFieldNull Then
             'Turn the mask off so you can save an empty record
             MaskEdBox1.Mask = ""
             MaskEdBox1.Text = ""
             Data1.UpdateRecord 'update the bound controls
          End If
   
       End If
   End Sub

STATUS

This behavior is by design.

MORE INFORMATION

Steps to Reproduce Behavior

1. Create a new project. Add the Masked Edit Control to the project.

1. Add a Data Control to Form1.

2. Add a Masked Edit Control to Form1. Set the DataSource property to "Data1."

3. Add a Text Box to Form1. Set the DataSource property to "Data1."

4. Add the following code to Form1:

         Dim bFieldNull As Boolean
         Dim db As Database
         Dim rs As Recordset
   

         Private Sub Form_Load()
             'Create a table with a phone field. Put some records into it.
             'Some records will have a phone value, some will be empty
      
             Dim fd As Field
             Dim td As TableDef
             Dim i As Integer
      
             On Error GoTo myerr ' The next line will cause an error if the
                                 'database already exists
      
             'Create a database containing a table, "Table1", which contains
             'one field, "Phone".
             Set db = Workspaces(0).CreateDatabase("MaskTest", _
                 dbLangGeneral)
             Set td = db.CreateTableDef("Table1")
             Set fd = td.CreateField("Phone", dbText, 14)
             fd.AllowZeroLength = True
             td.Fields.Append fd
             db.TableDefs.Append td
      
             'Add data to the Phone Field for even number records. The Phone
             'Field for odd number records will remain null.
             Set rs = db.OpenRecordset("table1")
             For i = 1 To 6
                 rs.AddNew
                 If i Mod 2 = 0 Then
                     rs("phone") = "(234) 654-9876"
                 End If
                 rs.Update
             Next
      
             db.Close
             LoadTable 'Call the LoadTable sub
             Exit Sub
      
         myerr:
             LoadTable 'Call the LoadTable sub
         End Sub
      
         Private Sub LoadTable()
             'Set the Recordset for the Data Control to all the records
             'in Table1 and bind the Phone field to the Masked Edit control.
             Set db = DBEngine(0).OpenDatabase("MaskTest")
             Set rs = db.OpenRecordset("Table1")
             rs.MoveFirst
             Set Data1.Recordset = rs
             MaskEdBox1.Mask = "(###) ###-####"
             text1.DataField = "Phone"
             MaskEdBox1.DataField = "Phone"
         End Sub
   
   

5. Press the F5 key to run the application.

6. Move through the records using the Data Control. Note that the Masked Edit Control does not update properly when the bound field is null. To work around this problem so that the Masked Edit control shows empty records when the bound field's value is null, add the code from the RESOLUTION section in this article to the Form1. Press the F5 key to run the application.

   (c) Microsoft Corporation 1997, All Rights Reserved.