Testing the COven Class

Testing the COven Class

Now you need to write a shell program that can be used to test your new class. Figure 16.3 shows a form that can be used to test the COven class.

Figure 16.3. A form for testing the COven class.

There are two buttons on the form. The btnUpdate button is used to update the state of the COven object, and the btnExit button is used to end the program.

The txtOvenTemp text box is a little different from other text boxes you have used so far in this book. In this case, you have set the ReadOnly property to True instead its default value of False . Therefore, the user cannot enter anything into the text box.

There are a number of radio button objects on the form. The names of the radio buttons should make it easy for you to decipher their use in the program. For example, the Bake, Broil, Clean, and Off radio buttons are named rbOvenOn , rbBroil , rbClean , and rbOvenOff . Equally obvious names are used for the other radio buttons. The names of the buttons, along with the code in the following section, make it clear what the purpose of each button is.

The Code for Testing the COven Class

The code for testing the COven class is somewhat long, but it's not too complicated. The code is presented in Listing 16.3.

Listing 16.3 Code for Testing the COven Class

 Option Explicit On Option Strict On Public Class frmOvenTest  Inherits System.Windows.Forms.Form  Private Const BROILTEMP As Integer = 550    ' Broiler temperature  Private Const CLEANTEMP As Integer = 600   ' Self-clean temperature  Dim MyOven As New COven()  Private Sub btnUpdate_Click(ByVal sender As System.Object, _        ByVal e As System.EventArgs) Handles btnUpdate.Click   ' Purpose: This button acts upon the state of the oven data as set   '      by the radio buttons and the text boxes.   If CheckSettings() = 0 Then  ' See if everything in proper state    Exit Sub   End If   If rbOvenOff.Checked = True Then    txtTemp.Text = "0"   End If   UpdateOvenTemperature()   txtTemp.Text = txtOvenTemp.Text  End Sub  Private Sub UpdateOvenTemperature()   ' Purpose: This routine compares the current oven temperature to   '      the desired temperature and updates it. To add a little   '      realism to the process, the change is delayed by using   '      the VBN DateDiff() function.   '   ' Argument list:   '  None   '   ' Return value:   '  N/A   Dim Start, Finish As Double   Dim NewDate As Date   Dim StartTemp, EndTemp, DiffTemp, Increments, Offset As Integer   StartTemp = CInt(txtOvenTemp.Text)   EndTemp = CInt(txtTemp.Text)   Increments = 5   Offset = 5   DiffTemp = EndTemp - StartTemp   If DiffTemp < 0 Then     ' If we are decreasing the temp    DiffTemp = 0 - DiffTemp   ' Make it positive    Increments = -5       ' Count down rather than up   End If   While DiffTemp > 0    NewDate = DateAdd(DateInterval.Second, 1, Now) ' Delay about a second    While DateDiff(DateInterval.Second, Now, NewDate) > 0     ' An empty loop    End While    StartTemp += Increments    DiffTemp -= Offset    txtOvenTemp.Text = CStr(StartTemp)    Me.Update()                  ' Update the form   End While  End Sub  Private Function CheckSettings() As Integer   ' Purpose: This subroutine simply checks to see if all   '      the radio buttons are consistent with   '      the action being done   '   ' Argument list:   '  N/A   '   ' Return value:   '  integer  True if OK, False otherwise   ' Is the oven on?   If rbOvenOff.Checked = True Then    txtTemp.Text = "0"    txtOvenTemp.Text = "0"    MessageBox.Show("The oven is off")    Return 0   End If   ' Broiling usually has oven door open   If rbDoorClosed.Checked = True And rbBroil.Checked = True Then    MessageBox.Show("Probably should open the oven door")    If txtTemp.Text = "0" Then     txtTemp.Text = CStr(BROILTEMP)    End If    Return 0   End If   ' If we are baking or self-cleaning, close the door   If rbDoorClosed.Checked = False And rbBroil.Checked <> True Then    If rbClean.Checked = False Then     Beep()     MessageBox.Show("Things bake faster with oven door closed")     Return 0    End If   End If   ' Show the temperature   If rbDoorClosed.Checked = False And rbBroil.Checked = True Then    txtTemp.Text = CStr(BROILTEMP)    Return -1   End If   ' If we are cleaning the oven...   If rbDoorClosed.Checked = False And rbClean.Checked = True Then    Beep()    MessageBox.Show("Close door during self-cleaning")    Return 0   End If   ' ...set the temperature to the max.   If rbDoorClosed.Checked = True And rbClean.Checked = True Then    txtTemp.Text = CStr(CLEANTEMP)    Return -1   End If   Return -1  End Function  Private Sub Form1_Load(ByVal sender As System.Object, _             ByVal e As System.EventArgs) Handles MyBase.Load   InitializeOven(MyOven)  End Sub  Private Sub InitializeOven(ByVal MyOven As COven)   ' Purpose: This sets up the starting state of the oven as shown by   '      the text boxes.   '   ' Argument list:   '  MyOven    a COven object. This does not really need to be   '         passed in since it has module scope. However,   '         doing it this way would allow us to change its   '         scope and still be able to use this procedure   '         without changing this code.   '   ' Return value:   '  N/A   If MyOven.OvenStatus = 0 Then   ' Show oven status    rbOvenOff.Checked = True   Else    rbOvenOn.Checked = True   End If   If MyOven.DoorStatus = 0 Then   ' Show door status    rbDoorClosed.Checked = True   Else    rbDoorOpen.Checked = True   End If   If MyOven.DoorStatus = 0 Then   ' Show door status    rbDoorClosed.Checked = True   Else    rbDoorOpen.Checked = True   End If   If MyOven.LightStatus = 0 Then  ' Oven light    rbLightOff.Checked = True   Else    rbLightOn.Checked = True   End If   txtTemp.Text = CStr(MyOven.Temperature)   ' Temperature   txtOvenTemp.Text = CStr(MyOven.Temperature)  End Sub  Private Sub btnExit_Click(ByVal sender As System.Object, _        ByVal e As System.EventArgs) Handles btnExit.Click   Me.Dispose()  End Sub  ' ================= The radio buttons =========================  Private Sub rbOvenOn_Leave(ByVal sender As Object, _        ByVal e As System.EventArgs) Handles rbOvenOn.Leave   rbOvenOn.Checked = True   MyOven.OvenStatus = -1  End Sub  Private Sub rbOvenOff_Leave(ByVal sender As Object, _        ByVal e As System.EventArgs) Handles rbOvenOff.Leave   rbOvenOff.Checked = True   MyOven.OvenStatus = 0  End Sub  Private Sub rbLightOn_Leave(ByVal sender As Object, _        ByVal e As System.EventArgs) Handles rbLightOn.Leave   rbLightOn.Checked = True   MyOven.LightStatus = 0  End Sub  Private Sub rbLightOff_Leave(ByVal sender As Object, _        ByVal e As System.EventArgs) Handles rbLightOff.Leave   rbLightOff.Checked = True   MyOven.LightStatus = 0  End Sub  Private Sub rbDoorOpen_Leave(ByVal sender As Object, _        ByVal e As System.EventArgs) Handles rbDoorOpen.Leave   rbDoorOpen.Checked = True   MyOven.DoorStatus = -1  End Sub  Private Sub rbDoorClosed_Leave(ByVal sender As Object, _        ByVal e As System.EventArgs) Handles rbDoorClosed.Leave   rbDoorClosed.Checked = True   MyOven.DoorStatus = 0  End Sub  Private Sub rbBroil_Leave(ByVal sender As Object, _        ByVal e As System.EventArgs) Handles rbBroil.Leave   If rbDoorClosed.Checked = True And rbBroil.Checked = True Then    MessageBox.Show("Probably should open the oven door")    Exit Sub   End If   MyOven.Broil()   txtTemp.Text = CStr(BROILTEMP)  End Sub  Private Sub rbClean_Leave(ByVal sender As Object, _        ByVal e As System.EventArgs) Handles rbClean.Leave   MyOven.SelfClean()   txtTemp.Text = CStr(CLEANTEMP)  End Sub  ' ============= the text boxes ========================  Private Sub txtTemp_Leave(ByVal sender As Object, _        ByVal e As System.EventArgs) Handles txtTemp.Leave   If txtTemp.Text = "0" Then    MyOven.Temperature = 0    rbOvenOff.Checked = True   End If  End Sub End Class 

The code in Listing 16.3 begins by defining two symbolic constants for the broiling and self-cleaning temperatures . Next it defines a COven class object named MyOven . Because the MyOven definition occurs outside any procedure, it has module scope. If this were a live program, it would be a good idea to place the definition of MyOven inside a procedure to hide it from the rest of the program.

All the action focuses on what happens when the user clicks the Update button. In the btnUpdate object's Click event, the code calls CheckSettings() to see if the radio buttons are in a state that allows the user to operate the oven. For example, if the rbOvenOff button is selected, the oven cannot do anything. If the rbBake button is selected but the oven door is open, an error message is issued. (Trying to bake something with the oven door open slows down the process a bunch.) You can read through the code and see what other states are examined.

The following code fragment is used to inject a small delay each time the txtOvenTemp text box is updated:

 While DiffTemp > 0   NewDate = DateAdd(DateInterval.Second, 1, Now) ' Delay about a second  While DateDiff(DateInterval.Second, Now, NewDate) > 0   ' An empty loop  End While  StartTemp += Increments  DiffTemp -= Offset  txtOvenTemp.Text = CStr(StartTemp)  Me.Update()                  ' Update the form End While 

The DateAdd() function sets the date interval to 1 second, and the second parameter to the call creates a 1-second difference between the current date (as held in Now ). The return value is assigned to NewDate , which is 1 second in the future. The While loop simply wastes time until the difference between NewDate and Now becomes . The remainder of the code updates the displayed oven temperature and updates txtOvenTemp on the form.

The code in Listing 16.3 actually updates things in less than 1 second, probably because of the time lag between the two calls to DateAdd() and DateDiff() . You can experiment with the second parameter in DateAdd() to see the impact it has on the delay.