Please help, VB.net I need help to understand I have most of the problem

[Spicychik89]

I am having trouble with excercise 1 and 2

1. Greencar will suppress the parent's Gaslow event so that objects based on GreenCar will not be able to respond to the Gaslow as is. Instead, when Gaslow fires, GreenCar will raise its own GasLow - you may use a different name- But only if the gas is at 2 or less gallons.

2. On the client side, divide the form in two areas, one for Car and another for GreenCar. Make sure each has the needed controls to enter each car's data, with two sets of buttons to Drive, and Pump Gas. However, since both sets of Drive and Pump Gas buttons will do the same actions; handle these events in one handler per button. For example handle Car and GreenCar's Drive click events in one handler, and do the same for the Pump Gas buttons.

Public Class Car

Dim mVinNumber As String
Dim mGasLevel As Single
Dim mMileage As Single
Dim mMpg As Single



Public Property VinNumber() As String
Get
Return mVinNumber
End Get
Set(ByVal value As String)
mVinNumber = value
End Set
End Property


Public Property GasLevel() As Single
Get
Return mGasLevel
End Get
Set(ByVal value As Single)
If value > 0 then
mGasLevel = value
End If
End Set
End Property


Public Property Mileage() As Single
Get
Return mMileage
End Get
Set(ByVal value As Single)
If value > 0 then
mMileage = value
End If
End Set
End Property

Public Property Mpg() As Single
Get
Return mMpg
End Get
Set(ByVal value As Single)
If value > 0 then
mMpg = value
End If
End Set
End Property

Public Sub Drive(ByVal Miles As Single)
Dim Range As Single = mMpg * mGasLevel 'current capacity
If Miles > Range Then
Messagebox.show("not enought gas to drive that far")
ElseIf Miles > 0 Then
Mileage += Miles 'increase mileage

GasLevel -= (Miles / MPG) 'decrease gas
Else
Messagebox.show("Enter a positive amount of miles to drive")
End If
End Sub

Public Sub PumpGas(ByVal Gallons As Single)
If Gallons > 0 Then
GasLevel += Gallons 'note we are not checking for max tank capacity
Else
Messagebox.show("Please enter a postive number for Gallons")
End Sub

End Class

----------------------------------------------------------------------------------------------------------------

Public Class fmDrive

Dim myCar As Car

Private Sub btnCreate_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnCreate.Click

'not required but a nice touch - check if user wants to throw away old car
Dim Proceed As Boolean = True
If mycar <> Nothing Then

If Messagebox.show("your current car will be destroyed. Continue?","New Car",Messageboxbuttons.YesNo) = DialogResult.No Then
Proceed = False
End If
End If

If Proceed Then

myCar = New Car(CStr(txtVIN.Text), CSng(txtMileage.Text), CSng(txtGasLevel.Text), CSng(txtMPG.Text))
UpdateDisplay()
End If



End Sub

Private Sub btnDrive_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnDrive.Click
If myCar Is Nothing Then
MessageBox.Show("You must create a car first before you drive.", "No Car Has Been Created Yet")
Else
myCar.Drive(CSng(InputBox("How many miles to drive?")))
UpdateDisplay()
End If

End Sub

Private Sub btnPump_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnPump.Click
If myCar Is Nothing Then
MessageBox.Show("You must create a car first before you pump gas.", "No Car Has Been Created")
Else
myCar.PumpGas(CSng(InputBox("How much gas to pump into the car?")))
UpdateDisplay()
End If

End Sub

Private Sub UpdateDisplay()
txtGasLevel.Text = myCar.GasLevel.ToString()
txtMileage.Text = myCar.Mileage.ToString()
txtMPG.Text = myCar.MPG.ToString()
txtVIN.Text = myCar.VIN

End Sub

Private Sub btnReset_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnReset.Click
If mycar <> Nothing then

myCar = Nothing 'kill a car

txtGasLevel.Clear()
txtMPG.Clear()
txtMileage.Clear()
txtVIN.Clear()
Else
Messagebox.show("Nothing to kill")
End If


End Sub



Private Sub btnExit_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnExit.Click
Me.Close()
End Sub
End Class

[.paul.]

Where's the GasLow Event???
You need to declare a Public Event in your Car class, raise that event at the appropriate time, then handle that event in fmDrive

https://msdn.microsoft.com/en-us/library/ms973905.aspx

[.paul.]

It also says you should have a GreenCar class, so i'm not sure how you're supposed to suppress the Event or even that an Event is necessary if you follow the specifications. Events are used when you create instances of classes, such as your myCar instance. Maybe you need a GreenCar instance too?

[jmcilhinney]

Firstly, please use formatting tags when posting code snippets for readability. Here's how your code should look:

Public Class Car
 
    Dim mVinNumber As String
    Dim mGasLevel As Single
    Dim mMileage As Single
    Dim mMpg As Single
 
 
 
    Public Property VinNumber() As String
        Get
            Return mVinNumber
        End Get
        Set(ByVal value As String)
            mVinNumber = value
        End Set
    End Property
 
 
    Public Property GasLevel() As Single
        Get
            Return mGasLevel
        End Get
        Set(ByVal value As Single)
            If value > 0 then 
            mGasLevel = value
            End If
        End Set
    End Property
 
 
    Public Property Mileage() As Single
        Get
            Return mMileage
        End Get
        Set(ByVal value As Single)
            If value > 0 then
            mMileage = value
            End If
        End Set
    End Property
 
    Public Property Mpg() As Single
        Get
            Return mMpg
        End Get
        Set(ByVal value As Single)
           If value > 0 then
            mMpg = value
            End If
        End Set
    End Property
 
   Public Sub Drive(ByVal Miles As Single)
        Dim Range As Single = mMpg * mGasLevel  'current capacity
        If Miles > Range Then 
        Messagebox.show("not enought gas to drive that far")
        ElseIf Miles > 0 Then
        Mileage += Miles  'increase mileage
        
        GasLevel -= (Miles / MPG)  'decrease gas
        Else
        Messagebox.show("Enter a positive amount of miles to drive")
        End If
    End Sub
 
    Public Sub PumpGas(ByVal Gallons As Single)
        If Gallons > 0 Then
        GasLevel += Gallons   'note we are not checking for max tank capacity
        Else
        Messagebox.show("Please enter a postive number for Gallons")
    End Sub
 
End Class
 
Public Class fmDrive
 
    Dim myCar As Car
 
    Private Sub btnCreate_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnCreate.Click
 
        'not required but a nice touch - check if user wants to throw away old car
        Dim Proceed As Boolean = True
        If mycar <> Nothing Then
        
        If Messagebox.show("your current car will be destroyed. Continue?","New Car",Messageboxbuttons.YesNo) = DialogResult.No Then
        Proceed = False
        End If
        End If
        
        If Proceed Then
    
        myCar = New Car(CStr(txtVIN.Text), CSng(txtMileage.Text), CSng(txtGasLevel.Text), CSng(txtMPG.Text))
        UpdateDisplay()
        End If
        
        
 
    End Sub
 
    Private Sub btnDrive_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnDrive.Click
        If myCar Is Nothing Then
            MessageBox.Show("You must create a car first before you drive.", "No Car Has Been Created Yet")
        Else
            myCar.Drive(CSng(InputBox("How many miles to drive?")))
            UpdateDisplay()
        End If
        
    End Sub
 
    Private Sub btnPump_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnPump.Click
        If myCar Is Nothing Then
            MessageBox.Show("You must create a car first before you pump gas.", "No Car Has Been Created")
        Else
            myCar.PumpGas(CSng(InputBox("How much gas to pump into the car?")))
            UpdateDisplay()
        End If
 
    End Sub
 
    Private Sub UpdateDisplay()
        txtGasLevel.Text = myCar.GasLevel.ToString()
        txtMileage.Text = myCar.Mileage.ToString()
        txtMPG.Text = myCar.MPG.ToString()
        txtVIN.Text = myCar.VIN
       
    End Sub
 
    Private Sub btnReset_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnReset.Click
        If mycar <> Nothing then
        
        myCar = Nothing 'kill a car
 
        txtGasLevel.Clear()
        txtMPG.Clear()
        txtMileage.Clear()
        txtVIN.Clear()
        Else
        Messagebox.show("Nothing to kill")
       End If
        
 
    End Sub
 
    
 
    Private Sub btnExit_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnExit.Click
        Me.Close()
    End Sub
End Class

As for the issue, I would suggest that you follow the Blog link in my signature below and check out my post on Custom events. It will show you that you should declare an OnSomeEvent method to raise the SomeEvent event. You can then suppress that event in a derived class by overriding that method and not calling the base method. If you need to raise a different event instead, you can do that in the overridden method.