If you are not a paid subscriber, you must have signed up for our free trial at http://www.codeoftheweek.com. Our ezine is not an unsolicited message (in other words a spam email). Keep in mind that if you signed up for our free trial you can still receive a total of four issues at no cost to you. After you receive the four issues you will be notified about continuing your subscription.
If you do not wish to continue to receive this ezine, please email us at cancel@codeoftheweek.com
The source code in this issue is designed for Visual Basic 5.0 and above. This is due to the use of the new AddressOf feature of VB 5. AddressOf allows you to pass the address of a subroutine created in a code module.
If you have any questions about this issue, please email us at questions@codeoftheweek.com
This issue introduces a Timer class to be used without any forms or controls. It is designed to be as close to the built-in control Timer that VB includes. It uses two API calls (SetTimer and KillTimer) to accomplish this task.
The methods/properties in this class will be shown below. There are two properties and one method you need to be aware of.
Public Property Let Interval(lInterval As Long) Public Property Get Interval() As Long
The Interval property sets the timer interval in milliseconds. For example, if you want a the timer to fire every 10 seconds, you would set Interval to 10,000. If a timer is currently active, it will disable the current timer and start a new timer with the updated Interval
Public Sub CallBackProc(lCallBackProc As Long)
The CallBackProc is the subroutine that the timer will call when it ticks off each Interval. We would have liked this to be a property, but the AddressOf keyword does not seem to be supported in a property statement. The subroutine you declare as your callback routine must be in a standard code module and have the following declaration:
Private Sub SampleTimerProc(ByVal hwnd As Long, _
ByVal uMsg As Long, _
ByVal idEvent As Long, _
ByVal dwTime As Long)
' Do your stuff here
End Sub
You can use the dwTime to determine exactly how much time has elapsed between each timer tick. This number is also in milliseconds. You should ignore the other parameters for this class module (If you want more information, check out the documentation for SetTimer).
Public Property Let Enabled(bEnabled As Boolean) Public Property Get Enabled() As Boolean
The enabled property works just like you think it would. If you set Enabled = True the timer will start ticking. If you set it to False, it will stop. If any errors occur here, they will be raised. If an error occurs starting or stopping the timer, an error number of 1 will be raised with an appropriate description.
This example shows how to use the cTimer class.
In a Code Module we declared this:
Public Sub MyTimerCallback(ByVal hwnd As Long, _
ByVal uMsg As Long, _
ByVal idEvent As Long, _
ByVal dwTime As Long)
Form1.Label1 = Val(Form1.Label1) + 1
End Sub
On Form1 we created three buttons (cmdStart, cmdStop, cmdChange) and a text box (txtTimer).
Dim oTimer As New cTimer
Private Sub cmdStart_Click()
' Start up the timer
oTimer.CallBackProc AddressOf MyTimerCallback
oTimer.Interval = Val(txtTimer.Text)
oTimer.Enabled = True
End Sub
Private Sub cmdStop_Click()
' Stop the timer
oTimer.Enabled = False
End Sub
Private Sub cmdChange_Click()
' Change the interval on the timer
oTimer.Interval = Val(txtTimer.Text)
End Sub
To see the source code for this issue you must be a subscriber to Code of the Week. If you are a subscriber the source code is available at the following address: http://www.codeoftheweek.com/membersonly/bi/0048.html
That concludes this issue of COTW. We hope you find the source code useful in your development.
The below describes the ways you can supply us some feedback about COTW. We would like to see our members help mold COTW into the best Visual Basic source code resource available. But to do that we need your feedback about what you like and what you do not like about COTW.
If you are interested in advertising in COTW please email us at sponsor@codeoftheweek.com Our rates are VERY reasonable, actually they are almost FREE. We reach over three thousand Visual Basic developers each week.
If you have any suggestions for topics you would like to see covered or questions about this issue, please email them to info@codeoftheweek.com or use online feedback form at http://www.codeoftheweek.com/feedback.html.
If you have any source code you would like to submit for possible inclusion in COTW, please fill out our online submission form at http://www.codeoftheweek.com/submission.html.
Thank you for trying Code of the Week for Visual Basic.
Your free trial expires after you receive your fourth issue. If you want to continue to receive Code of the Week you can get 52 issues of COTW for only $19.95. This is a full year of Visual Basic source code and information to help with all your development. So don't wait, subscribe now! The quickest way to subscribe is to jump to our online order form at http://www.codeoftheweek.com/order.html