Access Cookbook 2nd Edition-Access Cookbook 2nd Edition

Recipe 9.10 Create a Generic, Reusable Status Meter

9.10.1 Problem

Access allows you to control the built-in status meter using the SysCmd function, but you have no control over the location or appearance of this status meter. How do you create a status meter that you can control?

9.10.2 Solution

You can create a status meter based on an Access form and control it using VBA routines. The status meter is composed of a Rectangle control and a Label control. By updating the Width property of the rectangle, you can control the meter's progress. Additionally, by updating the Caption property of the label, you can insert messages such as "50% complete." All the internal workings of the control can be encapsulated (hidden) inside the form.

For an example of a programmatically controlled status bar, open and run frmTestStatusMeter from 09-10.MDB (see Figure 9-32). To start the status meter, click the Start button and frmStatusMeter will pop up. If you want the status meter to include a Cancel button, check the Include Cancel button checkbox before clicking the Start button. The status meter will slowly advance to 100% and then close. If you've included a Cancel button, you can click on it at any time to immediately close the status meter and notify the calling form (frmTestStatusMeter) that the cancel has been requested.

Figure 9-32. The frmStatusMeter form

9.10.2.1 Create a generic status meter

To create a generic status meter for your own application, follow these steps (or skip these steps entirely and import frmStatusMeter and basStatusMeter from 09-10.MDB into your database):

Create a form and set its properties as shown in Table 9-10.

Table 9-10. Property settings for the status bar form

Property

Value

DefaultView

Single Form

ScrollBars

Neither

RecordSelectors

No

NavigationButtons

No

PopUp

Yes

BorderStyle

Thin

Control Box

No

MinMaxButtons

None

Close Button

No

Place a rectangle on the form, name it recStatus, and set its Width property to 0. Set its background color to the color of your choice.
Place a label on the form, name it lblStatus, and set its Width property to the total width you want the status bar to be. Set its Background to Clear. In the Label property, type in "0% Completed".
Add a command button control named cmdCancel with a caption of "Cancel". Create an event procedure attached to the button's Click event. (If you're unsure of how to do this, see the Section P.5.5 in the the preface of this book.) Add the following code to the event procedure:
```
Private Sub cmdCancel_Click( )
    mblnCancel = True
End Sub
```
Add the following global declaration to the global declarations section of the form's module:
```
Dim mblnCancel As Boolean
```

Add the following three procedures to the form's module:

Private Sub cmdCancel_Click( )
    mblnCancel = True
End Sub

Public Sub InitMeter( _
  blnIncludeCancel As Boolean, strTitle As String)
   
   Me.recStatus.Width = 0
   Me.lblStatus.Caption = "0% complete"
   Me.Caption = strTitle
   Me.cmdCancel.Visible = blnIncludeCancel
   
   DoCmd.RepaintObject
   
   mblnCancel = False

End Sub

Public Property Let Value(intValue As Integer)
   Me.recStatus.Width = CInt(Me.lblStatus.Width * (intValue / 100))
   Me.lblStatus.Caption = Format$(intValue, "##") & "% complete"
   
   DoCmd.RepaintObject

End Property

Public Property Get Cancelled( ) As Boolean
   Cancelled = mblnCancel
End Property

Save the form as frmStatusMeter and close it.

Create a new global module and add the following code (or import the module basStatusMeter from 09-10.MDB).

Private Const mconMeterForm = "frmStatusMeter"

Private Function IsOpen(strForm As String)
    IsOpen = (SysCmd(acSysCmdGetObjectState, acForm, strForm) > 0)
End Function

Public Sub acbCloseMeter( )
   
    On Error GoTo HandleErr
   
    DoCmd.Close acForm, mconMeterForm

ExitHere:
    Exit Sub

HandleErr:
    Select Case Err.Number
        Case Else
            MsgBox "Error#" & Err.Number & ": " & Err.Description, , _
             "acbCloseMeter"
    End Select
    Resume ExitHere
End Sub

Public Sub acbInitMeter(strTitle As String, fIncludeCancel As Boolean)
   
    On Error GoTo HandleErr
    
    DoCmd.OpenForm mconMeterForm
    Forms(mconMeterForm).InitMeter fIncludeCancel, strTitle
   
ExitHere:
    Exit Sub

HandleErr:
    Select Case Err.Number
        Case Else
            MsgBox "Error#" & Err.Number & ": " & Err.Description, , _
             "acbInitMeter"
    End Select
    If IsOpen(mconMeterForm) Then
        Call acbCloseMeter
    End If
    Resume ExitHere
End Sub

Public Function acbUpdateMeter(intValue As Integer) As Boolean
   
    On Error GoTo HandleErr
    
    Forms(mconMeterForm).Value = intValue
    
    ' Return value is False if cancelled
    If Forms(mconMeterForm).Cancelled Then
        Call acbCloseMeter
        acbUpdateMeter = False
    Else
        acbUpdateMeter = True
    End If
   
ExitHere:
    Exit Function
HandleErr:
    Select Case Err.Number
        Case Else
            MsgBox "Error#" & Err.Number & ": " & Err.Description, , _
             "acbUpdateMeter"
    End Select
    If IsOpen(mconMeterForm) Then
        Call acbCloseMeter
    End If
    Resume ExitHere
End Function

Save and close the global module.

9.10.2.2 Use the generic status meter in your application

To use the generic status meter in your own applications, follow these steps:

When you wish to initialize the meter, use the following syntax:
```
Call acbInitMeter(title, flag)
```
where title is the title you want the status meter to assume, and flag is True (or -1) to display a Cancel button or False (or 0) to not display one. For example, this statement creates a status meter with the title Progress and a Cancel button:
```
Call acbInitMeter("Progress", True)
```
To update the meter with a new progress value, use the following syntax:
```
variable = acbUpdateMeter(value)
```
where value is an integer between 0 and 100. acbUpdateMeter will place True or False in the return value. If the return value is False, the user has pressed the Cancel button. (The return value will never be False if you choose not to include the Cancel button when initializing the status meter.) For example, to update the meter with a progress setting of 50%, you might call acbUpdateMeter like this:
```
blnOK = acbUpdateMeter(50)
```
To close the status meter form, use this syntax:
```
Call acbCloseMeter
```

9.10.3 Discussion

You can change the size of the rectangle by manipulating its Width property. The Rectangle control is placed behind a transparent Label control that defines the boundaries of the status meter and contains the status text. The status meter form is manipulated by three public wrapper functions contained in basStatusMeter: acbInitMeter, acbUpdateMeter, and acbCloseMeter. These functions, in turn, interact with frmStatusMeter through its exposed properties. The wrapper functions know the names of the properties and how to call them, but they know nothing of the inner workings of the form.

acbInitMeter initializes the status meter by opening the status meter form and calling the InitMeter method. At the same time, a parameter is passed that determines if the Cancel button is included on the status meter form:

DoCmd.OpenForm acbcMeterForm
Forms(acbcMeterForm).InitMeter blnIncludeCancel, strTitle

acbUpdateMeter sets the value of the status meter form's UpdateMeter property. It then checks the Cancelled property of the form to determine whether the user has clicked on the Cancel button. If so, it closes the status meter form and returns False to the calling procedure; otherwise it returns True:

Forms(acbcMeterForm).Value = intValue

' Return value is False if cancelled.
If Forms(acbcMeterForm).Cancelled Then
    Call acbCloseMeter
    acbUpdateMeter = False
Else
    acbUpdateMeter = True
End If

acbCloseMeter closes the status meter form using the DoCmd.Close method:

DoCmd.Close acForm, acbcMeterForm

When the InitMeter property is set by some external procedure, the InitMeter procedure runs the following code:

Me.recStatus.Width = 0
Me.lblStatus.Caption = "0% complete"
Me.Caption = strTitle
Me.cmdCancel.Visible = blnIncludeCancel

DoCmd.RepaintObject

mblnCancel = False

This code sets the Width property of the recStatus control to 0 and the Caption property of lblStatus to "0% complete", updates the form's Caption property with the strTitle parameter, and sets the cmdCancel button's Visible property to match the blnIncludeCancel parameter. The code then uses the RepaintObject method to force an update of the screen and resets the mblnCancel module-level global variable to False.

When the UpdateMeter property of the form is set to a value, the following code is executed by the UpdateMeter procedure:

Me.recStatus.Width = CInt(Me.lblStatus.Width * (intValue / 100))
Me.lblStatus.Caption = Format$(intValue, "##") & "% complete"

DoCmd.RepaintObject

This code updates the status meter by changing the width of the recStatus control relative to the width of the lblStatus control. This relative change ensures that the status meter rectangle never exceeds the limits as defined by the width of the lblStatus control. The routine then updates the Caption property of the lblStatus control to a formatted percentage value concatenated to the string "% complete". Once again, the code uses the RepaintObject method to force an update of the screen.

The Cancelled property of the status meter form is handled by the Cancelled Get property procedure. When called by an external procedure, this procedure returns the value of the module-level global mblnCancel variable. This variable, which was initialized to 0 by the IntitMeter Let property procedure, is set to False if the user clicks on the cmdCancel button in the cmdCancel_Click event procedure.

It's a good idea to encapsulate the inner workings of a generic utility form such as frmStatusMeter by keeping all the event procedures private and using procedures to expose a controlled user interface to calling procedures. Getting in the habit of thinking and coding in this object-oriented way will allow you to create generic components that you can reuse over and over again.

The pop-up status meter form's AutoCenter property has been set to Yes, so it will always appear in the center of the screen. You may wish to extend acbInitMeter with optional left and top parameters so you can precisely position the form on the screen when it is first opened.

[ Team LiB ]