Programming & Security

Posted: 25 Sep 2009 05:01 AM PDT

Last week we have seen the usage of Filter() Function with a simple example and I hope you understood how it works. We have assigned constant values to the Source Array elements directly to keep the VBA Code as simple as possible.

We can filter data on Forms by setting Criteria on the Filter Property of Forms. Similarly, we can use conditions in Queries to filter information from Tables as well.

But, the Filter() Function gives a unique way of filtering data from an Array of information loaded from Tables or Queries and create output quickly based on matching or non-matching options.

Let us try out the Filter() Function in an Address Book Application to quickly find persons or places that matches with the specified search text and display them in a List Box. We will use Names and Addresses from the Employees Table of Northwind.mdb sample database for our experiment.

Following is the User Interface design that we planned to create and explains how the User will interact with it to display information quickly on the Form.

We will design a Form with a List Box, a Text Box Control, a Check-Box Control and a Command Button for our experiment. An image of such a Form in Design View is given below:

When the Form is open in normal view the List Box and Text Box Controls will be empty. The User can enter the word ALL in the Text Box Control and click the Command Button to display the Name and Addresses of all Employees in the List Box.

Or

The User can enter a word or phrase, like part of a Name or Address, that can match anywhere within the Name and Address text, and click on the Command Button to filter out the matching items and to display them in the List Box.

If the Matching Cases Check-Box is in selected state then the Filter action will select records that matches with the search text given in the Text Box Control otherwise it will select all records that do not match with the search text.

To provide the User with the above facility we need two Subroutines on the Form's Code Module and a User Defined Function in Standard Module of the Database to use the Filter() Function.

When the User opens the above Form the first Sub-Routine is run from the Form_Load() EventProcedure to read the data (First Name, Last Name & Address) from Employees Table, join all the three field values into a single row of text and load them into a Singly Dimensioned Array Variable in Memory. This data will remain in memory till the User closes the Form.

The second Sub-Routine is run when the User clicks on the Command Button to extract information from the Source Array with the help of Filter() function, based on the search text entered into the Text Box Control.

The Filter() Function will extract the entries that matches with the search Text in the Text Box Control, from the Source Array Variable, and save the output into the target variable xTarget. All we have to do is to take these values, format and insert as Row Source Property Value to display them in the List Box.

Let us prepare for the Address Book's Quick Find Project.

Import Employees Table from C:\Program Files\Microsoft Office\Office11\Samples\Northwind.mdb sample database.

Open a new Form in Design View.

Select the List Box Control from the Tool Box and draw a List Box as shown on the design above.

While the List Box is in selected state display the Property Sheet (View - - > Properties) and change the following Property Values as given below:

Name = AddBook

Row Source Type = Value List

Width = 4.5"

Height = 1.75"

Font Name = Courier New

Font Size = 10

Position the Child Label attached to the List Box above and change the Caption value to Address Book.

Draw a Text Box below the List Box. Change the Name Property of the Text Box to xFind. Position the Child Label above the Text Box and change the Caption value to Search Text/ALL.

Create a Check-Box Control to the right of the Text Box. Change the Name Property of the Check-Box to MatchFlag. Change the Default Value Property to True. Change the Caption value of the child label to Matching Cases.

Create a Command Button to the right of the Check-Box control. Change the Name Property Value of the Command Button to cmdFilter and the Caption Property Value to Filter.

Name

Display the Code Module of the Form (View- - >Code).

Copy and paste the following Code into the Form Module:


Option Compare Database
Option Explicit
Dim xSource() As Variant

Private Sub Form_Load()
Dim db As Database, rst As Recordset, J As Integer
Dim FName As String * 12, LName As String * 12, Add As String * 20

'Take the count of records
J = DCount("*", "Employees")

'redimension the array for number of records
ReDim xSource(J) As Variant

Set db = CurrentDb
Set rst = db.OpenRecordset("Employees", dbOpenDynaset)
'load the name and addresses into the array
J = 0
Do Until rst.EOF
   FName = rst![FirstName]
   LName = rst![LastName]
   Add = rst![Address]
  xSource(J) = FName & LName & Add
rst.MoveNext
J = J + 1
Loop
rst.Close
Set rst = Nothing
Set db = Nothing
End Sub


Private Sub cmdFilter_Click()
Dim x_Find As String, xlist As String, xTarget As Variant
Dim x_MatchFlag As Boolean, J As Integer

Me.Refresh
x_Find = Nz(Me![xFind], "")
x_MatchFlag = Nz(Me![MatchFlag], 0)

'if no search criteria then exit
If Len(x_Find) = 0 Then
  Exit Sub
End If
    'initialize list box
    xlist = ""
    Me.AddBook.RowSource = xlist
    Me.AddBook.Requery

If UCase(x_Find) = "ALL" Then
    'Take all values from the Source Array
    'Format it as listbox items
    For J = 0 To UBound(xSource())
      xlist = xlist & xSource(J) & ";"
    Next
Else
    'Call the Filter Function
    xTarget = GetFiltered(xSource(), x_Find, x_MatchFlag)
    'format the returned values as list box items
    If Len(xTarget(0)) > 0 Then
        For J = 0 To UBound(xTarget)
            xlist = xlist & xTarget(J) & ";"
        Next
    End If
End If
    'remove the semicolon from
    'the end of the list box Value List
    If Len(xlist) > 0 Then
        xlist = Left(xlist, Len(xlist) - 1)
    End If
    'insert the list item string
    'and refresh the list box
    Me.AddBook.RowSource = xlist
    Me.AddBook.Requery

End Sub

Save the Form with the name Filter Form.

Copy and paste the following Function in a Standard Module and save the Module:


Public Function GetFiltered(ByRef SourceArray() As Variant, ByVal xFilterText As Variant, ByVal FilterType As Boolean) As Variant

GetFiltered = Filter(SourceArray, xFilterText, FilterType)

End Function

Filter()

Filter

Filter()

GetFiltered()

By Reference

Open the Filter Form in normal View.

Enter the word ALL (in this case the Matching Cases flag has no effect) in the Text Box control and Click on the Filter Command Button.

xSource()

Enter the text Ave in the Text Box and see that the Matching Cases check box is in selected state.

Click on the Command Button.

Ave

Remove the check-mark from the Matching Cases check box and click on the Filter Command Button again.

Now, all items except the lines with the word Ave are listed in the List Box.

If you go through the Programs that we have copied into the Form Module you can see that we have declared the xSource() Array Variable in the Global area of the Module so that we can use the data in both Sub-Routines in the Form Module.

In the Form_Load() Event Procedure we have declared three Variables as fixed length String Type (see the declaration line given below).

Dim FName As String * 12, LName As String * 12, Add As String * 20

When we read employee Name and Address into these Variables the values will be left justified inside the Variable and balance area of the declared size will be space filled to the right. This method will space out items in fixed distance from each other and properly aligned when displayed.

It is important that we use a Fixed Width Font, like Courier New, for the List Box display and we set this in Step-4 above.

If you click the Filter Command Button when the Text Box is empty then the program terminates, otherwise it calls the GetFiltered() Function by passing the parameter values.

The output Values are returned in the xTarget Array and the next steps formats the Value List and displays them in the List Box.