Lesson XIII.           Timer

 

Objectives

ü       To know how Timer works

ü       To use Timer control in time-dependent applications

 

 

 

 

The Timer control works in the background – you do not see it on the Form at runtime.  The primary purpose of a Timer is to trigger an event at a certain interval.  The following are the properties of a Timer.

Property	Description
Enabled	Determines whether the Timer can respond to events.
Index	Specifies the subscript of the control in a control array.
Interval	Specifies the number of milliseconds between calls to a Timer control’s Timer event.  The value must be within the range of 1 to 65535.  This value is in millisecond (or a thousandth of a second).

 

What can we do with a Timer? You may want to replace the caption property of a Label with another quotation every 5 seconds. You may want to simulate animation by replacing the image of an ImageBox every half a second.  Or you may simply want to give a time-pressured quiz – a sequence of questions appears one after another at an interval of 10 seconds.

 

The Timer has one event, the Time event.  The procedure <timer_name>.Timer( ) is executed every <interval_value> milliseconds.  The Timer control continues this until we disable the control by setting the Enabled property to False.

 

 

 

 

 

Let’s have some fun and create a small animation.  Animation involves a series of still images displayed in rapid sequence.  We will need several images of an object to be animated at different times.  For this application, we will make a dog walk. 

 

The following are the images that we will use:

 

 

The images are named dog1.wmf, dog2.wmf, dog3.wmf, dog4.wmf, and dog5.wmf.  You will later know why we have to make the names similar.

 

Follow these steps:

1.   Create a new Project.

2.   Drag an ImageBox to the Form and name it imgDog.  Set the Picture property to dog1.wmf (the initial snapshot of our dog).  Resize the ImageBox to the size you want.  Make sure that the Stretch property is set to True so that the image resizes to the size of the ImageBox.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

3. Drag a Timer to the Form.
4. What we want to do is to change the image every 80 milliseconds.  Thus, set the Interval property of the Timer to 80.
5. We have already displayed dog1.wmf.  We will have to display dog2.wmf, dog3.wmf, …, dog5.wmf, then back to dog1.wmf.  Add the following procedure:

 

Private Sub timTimer_Timer()

    imgDog.Picture = LoadPicture (App.Path + "\dog" & Trim(Str(x)) & ".wmf")

    If x < 5 Then

        x = x + 1

    Else

        x = 1

    End If

End Sub

 

What the above code does is to change the picture by calling the LoadPicture() function.  "\dog" & Trim(Str(x)) & ".wmf" specifies the filename of the image to be loaded and displayed.  Variables x serves as our counter. If x is currently one, then we load dog1.wmf.  If it is 2, then we load dog2.wmf.  Had we not named the pictures such, we will have to write the filenames lexically.

 

The first time timTimer_Timer() is called, we dog2.wmf should be loaded.  Hence, we have to initialize x to 2.  We do this during Form_Load().  We will have to declare in the general area with the Public keyword to make variable x accessible to all procedures.

 

Public x As Integer

 

Private Sub Form_Load()

    x = 2

End Sub

 

6.   Run the application.

7.   Save your work as Less13.vbp.

 

 

1.       Add a button to the Dog Animation application with caption “Pause”.  If the user presses the Pause button, the animation stops and the caption of the button changes to “Play”.  If the user clicks the Play button, animation resumes.

 

2.       Create an application.  Add a Label to the Form with the caption “Timer”.  Set the Font property to Arial, size 6.  Drag a Timer control as well.  Every second, add 3 points to the Label’s font size.  When the font size grows to a value that will make the caption too big for the Label, set the font size back to 6 points and start increasing the size once again.