[RESOLVED] IF..Catch and Class Exception

[EmilyM1105]

Can someone tell me if I did this the right way so far?? I know im missing part of the IF..Catch statement still..Im working on that.

Steps that I had to follow:

1. Make the LoginException class a custom exception by deriving from the Exception class.
2. In the Login procedure of the Main module, replace the two lines that read MessageBox.Show(“Incorrect password.”) with the following code: Throw New LoginException.
3. Add a Try...Catch statement for the following line in the btnLogin_Click event handler procedure: Main.Login(txtUsername.Text, txtPassword.Text) Add the following line to the Catch block: MessageBox.Show(“Incorrect password.”)

This is my LoginException code:

Public Class LoginException
    Inherits Exception
End Class

This is my Main.vb code

Module Main
    Friend blnLoggedIn As Boolean
    Dim arrUsernames() As String = {"Admin, Clerk, Manager"}
    Dim arrPasswords() As String = {"P@ssword, pa$$word, and passw0rd"}

    Sub Login(username As String, password As String)
        blnLoggedIn = False
        If VerifyUsername(username) And VerifyPassword(password) Then
            'Find index for username
            Dim userIndex As Integer
            For loopIndex = 0 To arrUsernames.Length - 1
                If arrUsernames(loopIndex) = username Then
                    userIndex = loopIndex
                    Exit For
                End If
            Next
            'Check for password match
            If arrPasswords(userIndex) = password Then
                blnLoggedIn = True
            Else
                Throw New LoginException
            End If
        End If

    End Sub
    Function VerifyUsername(username As String) As Boolean
        Return True
        'If the username is found, Return True, otherwise Return False
    End Function

And this is my LoginForm code:

Public Class LoginForm
    Private Sub Label1_Click(sender As Object, e As EventArgs) Handles lblUsername.Click, btnLogin.Click
        Login(txtUsername.Text, txtPassword.Text)
        Try
        Catch ex As LoginException
            MessageBox.Show(“Incorrect password.”)

        End Try
        If Main.blnLoggedIn Then
            MessageBox.Show(“Thank you for logging in, “ & txtUsername.Text, “Logged In.”)
            Me.Close()
        End If

    End Sub

    Private Sub btnCancel_Click(sender As Object, e As EventArgs) Handles btnCancel.Click
        Application.Exit()
    End Sub
End Class

[OptionBase1]

When using Try/Catch, you want the code that can trigger the exception to be inside of the Try statement. So you'll want to move the Login() statement after Try:

        Try
            Login(txtUsername.Text, txtPassword.Text)
        Catch ex As LoginException
            MessageBox.Show(“Incorrect password.”)
        End Try

[wes4dbt]

In the Login procedure of the Main module, replace the two lines that read MessageBox.Show(“Incorrect password.”) with the following code: Throw New LoginException.

This says to replace 2 lines but you only have 1 line that says Throw New LoginException. I don't see another line in the Login procedure that says "Incorrect Password" so either the instructions are wrong or your Login procedure isn't written the way the instructor wanted.

[EmilyM1105]

When using Try/Catch, you want the code that can trigger the exception to be inside of the Try statement. So you'll want to move the Login() statement after Try:

        Try
            Login(txtUsername.Text, txtPassword.Text)
        Catch ex As LoginException
            MessageBox.Show(“Incorrect password.”)
        End Try

ok I did that but when I try to debug it says it cant debug because there are build errors..The login word keeps saying end of statement expected??

vate Sub Label1_Click(sender As Object, e As EventArgs) Handles lblUsername.Click, btnLogin.Click
        Try Login(txtUsername.Text, txtPassword.Text)
        Catch ex As LoginException
            MessageBox.Show(“Incorrect password.”)
        End Try

[si_the_geek]

The word Try should be on a line by itself, as it was in OptionBase1's post.

You then have one or more lines (in this case the Login(...) line) in between the Try line and the Catch line.

[EmilyM1105]

The word Try should be on a line by itself, as it was in OptionBase1's post.

You then have one or more lines (in this case the Login(...) line) in between the Try line and the Catch line.

Oh ok thankyou for pointing that out!! I didnt think it mattered. I worked!

[EmilyM1105]

When using Try/Catch, you want the code that can trigger the exception to be inside of the Try statement. So you'll want to move the Login() statement after Try:

        Try
            Login(txtUsername.Text, txtPassword.Text)
        Catch ex As LoginException
            MessageBox.Show(“Incorrect password.”)
        End Try

Ok so since I have updated my codes:


This is my LoginForm code:

Public Class LoginForm
    Private Sub btnLogin_Click(sender As Object, e As EventArgs) Handles btnLogin.Click
        Try
            Login(txtUsername.Text, txtPassword.Text)
        Catch ex As LoginException
            MessageBox.Show(“Incorrect password.”)
        End Try
        If Main.blnLoggedIn Then
            MessageBox.Show(“Thank you for logging in, “ & txtUsername.Text, “Logged In.”)
            Me.Close()
        End If

    End Sub

    Private Sub btnCancel_Click(sender As Object, e As EventArgs) Handles btnCancel.Click
        Application.Exit()
    End Sub
End Class

This is my Main code:

Module Main
    Friend blnLoggedIn As Boolean
    Dim arrUsernames() As String = {"Admin", "Clerk", "Manager"}
    Dim arrPasswords() As String = {"P@ssword", "pa$$word", "passw0rd"}
    Dim userIndex As Integer

    Sub Login(username As String, password As String)
        blnLoggedIn = False
        If VerifyUsername(username) And VerifyPassword(password) Then
            blnLoggedIn = True
        Else
            Throw New LoginException
        End If

    End Sub

    Function VerifyUsername(username As String) As Boolean
        For loopIndex = 0 To arrUsernames.Length - 1
            If arrUsernames(loopIndex) = username Then
                userIndex = loopIndex
                Return True
            End If
        Next
        Return False
    End Function

    Function VerifyPassword(password As String) As Boolean
        'Check for password match
        If arrPasswords(userIndex) = password Then
            Return True
        Else
            Return False
        End If
    End Function

End Module

And this is my LoginException code:

Public Class LoginException
    Inherits Exception
End Class

Does everything look right to you for the set of instructions for this part??

[OptionBase1]

Yes, that all looks like it correctly follows what the instructions are. Does it compile and properly handle valid and invalid usernames and password?

[wes4dbt]

Reread Post #3

My guess is that the instructor wants this "Throw New LoginException" in the VerifyUserName and VerifyPasswoord functions.

[EmilyM1105]

Yes, that all looks like it correctly follows what the instructions are. Does it compile and properly handle valid and invalid usernames and password?

Yes it all works!! Now I have to make a new class with properties:


The GroceryItem class should contain the following public properties:

1. ScanNumber - Represents the unique serial code for the item on the shelf. This property should be read-only.

2. BrandName - The name as described on the item’s packaging

3. Description - A short description of the item

4. Price - The amount of money it costs to buy the item. Make sure that only positive values can be assigned to this property.

5. Aisle - This should indicate one of the following aisles: Bakery, CannedGoods, Drinks, Deli, DryGoods, FrozenFoods, and Produce.

This is my Grocery Item code:

Public Class GroceryItem
   ReadOnly ScanNumber As Integer
    Property BrandName As String
    Property Description As String
    Property Price As Integer
    Property Aisle As String
End Class

It says you can use enumeration.

The GroceryItem class should contain the following public constructors:

1. A constructor that accepts and sets only the ScanNumber property. Remember: If a property is read-only, then you’ll need to set the variable, not use the property name.

2. A constructor that accepts and sets the ScanNumber, BrandName and Price properties.

Add a new public class named GroceryBasket to the project.

1. Derive from the generic List class.
2. Ensure that only GroceryItem objects are stored as items.

Add the following variable declaration to the Main module: Friend basket As New GroceryBasket

Main Code:

Module Main
    Friend blnLoggedIn As Boolean
    Dim arrUsernames() As String = {"Admin", "Clerk", "Manager"}
    Dim arrPasswords() As String = {"P@ssword", "pa$$word", "passw0rd"}
    Dim userIndex As Integer
    Friend basket As New GroceryBasket

Test your work.

Note: You can add code to the btnLogin_Click event handler procedure to instantiate the GroceryItem class and add multiple objects to the GroceryBasket variable. Make sure you either remove or comment out this code after testing.

[OptionBase1]

Creating a property for a class is much more involved than the code you included. I don't know what textbook (if any) your programming class is using, but you might want to take a look at this page for some basic examples of how properties are implemented in a Class: https://www.dotnetperls.com/property-vbnet

That being said, you should start a new thread for this question.

[EmilyM1105]

ok i will

[Sitten Spynne]

For some reason that page doesn't load for me, but actually making a property doesn't have to be involved.

The traditional .NET property looks like this:

Private _backingField As TypeName

Public Property PropertyName() As TypeName
    Get
        Return _backingField
    End Get
    Set(ByVal value As TypeName)
        _backingField = value
    End Set
End Property

'TypeName' above is any .NET type like String or Form or a type you make yourself. A .NET property is a weirdo syntax sugar for saying, "I want a thing that behaves like a variable, but gives me the option of executing some code when the value is set or retrieved".

Having to type a minimum of 9 lines per property proved to get really old, really fast, as people started writing programs with hundreds of types and thus thousands of properties. It's especially tedious considering 99% of properties have the same implementation as the pattern above.

So around the VS 2010 timeframe, "auto properties" were added to the compiler. If you type this:

Public Property PropertyName() As TypeName

The compiler auto-generates the other 8 lines of code. You can also make a read-only auto-property:

Public ReadOnly Property PropertyName() As TypeName

This can be set inline or during the constructor, and nowhere else.

The problem is your assignment said it had to include "Public Properties". You didn't use the word "Public". That word is important, because it tells VB, "I'd like anything that has a GroceryItem to see these properties." When you don't use "Public", you get the default access specifier in VB. To find out what that is, you need to read the 200-page Visual Basic Language Specification. If that doesn't sound fun to you, then always make sure you put "Public", "Protected", "Private", or "Friend" in front of your properties. They each do different things, and any book/slides you have ought to explain the differences.

Aside from that advice, I don't see a question in your post #10. I see you pasted your assignment, but the only question that implies is "do it for me". My answer is, "No, but if you are stuck on a part and can explain what you've tried, I will help you with that part."

[wes4dbt]

The problem is your assignment said it had to include "Public Properties". You didn't use the word "Public". That word is important, because it tells VB, "I'd like anything that has a GroceryItem to see these properties."

Not sure you have to use the word "Public" anymore, in my VB 2015 test project the property is Public by default. Is would use it anyway, just as a matter of form but I don't believe it's required.

[EmilyM1105]

Not sure you have to use the word "Public" anymore, in my VB 2015 test project the property is Public by default. Is would use it anyway, just as a matter of form but I don't believe it's required.

Yea mine has it by default also

[Shaggy Hiker]

I wouldn't count on it, even if it is true. After all, if you get default wrong, then de fault is yours.

[Sitten Spynne]

Not sure you have to use the word "Public" anymore, in my VB 2015 test project the property is Public by default. Is would use it anyway, just as a matter of form but I don't believe it's required.

If you don't use it, you have to read the Visual Basic Language Specification to know what the default is. It could be subject to change between versions of VB. In general, being explicit is more important than being fast.

[si_the_geek]

It also isn't just a matter of knowing what the default is, but what the default is in the current situation - because some situations have different defaults.

Even if you know all the defaults, when reading the code you still need to think about which it is, and each time you do that it tends to waste more time than you saved from avoiding typing the extra word in the first place.

[wes4dbt]

As I said, I would use it anyway and I always have. But it did surprise me that Public was the default. I went and checked the default for Subs and Functions in a class and again to my surprise they default to public. Learn something new every. Won't change how I write my code though. Has VB .Net always been this way?

[wes4dbt]

Well, I tested VB 2010 and it behaves the same, don't have 2005 installed anymore. It just seems to me that MS would have them default to private, to keep code unexposed unless stated otherwise by using "Public".