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Taking Advantage of Built-In, Form-Filtering Features
Access has several form-filtering features that are part of the user interface. You can opt to include these features in your application, omit them from your application entirely, or control their behavior. For your application to control their behavior, it needs to respond to the Filter event, which it does by detecting when a filter is placed on the data in the form. When it has detected a filter, the code in the Filter event executes.Sometimes you might want to alter the standard behavior of a filter command. You might want to display a special message to a user, for example, or take a specific action in your code. You might also want your application to respond to a Filter event because you want to alter the form's display before the filter is applied. For example, if a certain filter is in place, you might want to hide or disable certain fields. When the filter is removed, you could then return the form's appearance to normal.Fortunately, Access not only lets you know that the Filter event occurred, it also lets you know how the filter was invoked. Armed with this information, you can intercept and change the filtering behavior as needed.When a user chooses Filter By Form or Advanced Filter/Sort, the FilterType parameter is filled with a value that indicates how the filter was invoked. If the user invokes the filter by selecting Filter By Form, the FilterType parameter equals the constant acFilterByForm; however, if she selects Advanced Filter/Sort, the FilterType parameter equals the constant acFilterAdvanced. The following code demonstrates how to use these constants:Private Sub Form_Filter(Cancel As Integer, FilterType As Integer)
Select Case FilterType
Case acFilterByForm
MsgBox "You Just Selected Filter By Form"
Case acFilterAdvanced
MsgBox "You Are Not Allowed to Select Advanced Filter/Sort"
Cancel = True
End Select
End Sub
This code, placed in the form's Filter event, evaluates the filter type. If the user selected Filter By Form, the code displays a message box, and the filtering proceeds as usual. However, if the user selected Advanced Filter/Sort, she's told she can't do this, and the filter process is canceled.Not only can you check how the filter was invoked, you can also intercept the process when the filter is applied. You do this by placing code in the form's ApplyFilter event, as shown in this example:Private Sub Form_ApplyFilter(Cancel As Integer, ApplyType As Integer)
Dim intAnswer As Integer
If ApplyType = acApplyFilter Then
intAnswer = MsgBox("You just selected the criteria: & _
Chr(13) & Chr(10) & Me.Filter & _
Chr(13) & Chr(10) & Are You Sure You Wish _
to Proceed?", vbYesNo + vbQuestion)
If intAnswer = vbNo Then
Cancel = True
End If
End If
End Sub
This code evaluates the value of the ApplyType parameter. If it's equal to the constant acApplyFilter, a message box is displayed, verifying that the user wants to apply the filter. If the user responds Yes, the filter is applied; otherwise, the filter is canceled.
