How to change value of a label and depending on numeric updown control?

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Hi, I'm really frustrated about this. I can't find any solution about this. I have a label and a numeric updown in my form and what I'm trying to do is to decrease the value of the label whenever the numeric updown is pressed up and increase the value of the label when the numeric updown is pressed down.

The label has a value of 100 and I want to decrease it whenever the numeric updown is pressed up and vice versa.

What I have tried:

VB

Private Sub numCategory_ValueChanged(sender As Object, e As EventArgs) Handles numCategory.ValueChanged

        Dim oldvalue As Integer


        If numCategory.Value > oldvalue Then

            lblpoints.Text -= 1

        ElseIf numCategory.Value < oldvalue Then


            lblpoints.Text += 1
        Else

            lblpoints.Text = ""

        End If

        oldvalue = numCategory.Value



    End Sub

I tried the above code it seems that it just make everything a mess.

Posted 4-Apr-20 18:40pm

lelouch_vi 2

Updated 5-Apr-20 0:52am

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OriginalGriff · Accepted Answer · 2020-04-04T19:59:00

Solution 1

Look at your code:

VB

Dim oldvalue As Integer

Declares oldvalue as a local variable, the value of which will be discarded when the method returns.

Move the declaration outside the method, and it'll start to work better. (Not perfect, but that's a bug you'll need to find and fix later - testing properly will show it up).

Posted 4-Apr-20 19:59pm

OriginalGriff

Comments

lelouch_vi 2 5-Apr-20 4:33am

Wow! thanks a lot. It works just like what I wanted. I'm wondering how does it behave that way? I put the oldvalue on a class level and it works fine now. Kindly please explain what did just happened?

OriginalGriff 5-Apr-20 4:59am

It's gets complicated, but I'll try to simplify it as much as I can. There are two type of memory in .NET: the heap, and the stack. Heap is where all the items you create with the New keyword are stored, the stack is much smaller, and holds information that is created and destroyed while your app runs. You call a method, it stores where to Return to on the stack, and allocates space on the stack for each of the variables the method will use (generally to store references to items on the Heap). When the method returns, that information is discarded (though the Heap data persists, the local references to it are discarded), and control is passed back to the place the method was called from.
It's like a stack of coins: put a piece of paper on the top, then add five coins: in order to read what is on the paper you have to remove the coins first. The paper is the return address, the coins are local variables.
So each time you call your method, the local variables are created all over again, qand have no idea what the previous content might have been - they start again from scratch.
Placing the definition of a variable outside any methods makes it part of the class, so it is not local any more, and isn't destroyed when the method exits.

That's a big (you no idea how big!) oversimplification, but without being able to see when your eyes start to glaze over it's hard to be any more precise! :laugh:

lelouch_vi 2 5-Apr-20 5:05am

haha!thank you for the effort to summarize half of my semester. I'm sorry for asking too many questions but I just want to clarify things so I can learn more.

lelouch_vi 2 5-Apr-20 4:39am

is it gonna be the same if I declare oldvalue as static inside the method?

lelouch_vi 2 5-Apr-20 4:47am

May I know what exactly happens with this line? lblpoints.Text -= 1 I have a "100" text on that "lblpoints" and I'm a little bit confuse with this expression
"lblpoints.Text -= 1" because it looks like it's decrementing the text value of the label even though it's a string?

OriginalGriff 5-Apr-20 5:12am

This is because VB is a crappy language.
What happens is that VB looks at your code and says to itself "Looks like he's trying to subtract a number from something - I'll convert the string into a number, subtract it, and change it back to a string when I'm finished". And most of the time that works, until something else happens, and suddenly the conversion fails and your app crashes for no obvious reason. That's why your Else clause is a bug - if it ever occurs, then next time the method is executed, the string is no longer a number and it all goes tits up without anything in your code changing.

This is called "weak typing" and it's just one of the reasons that people with experience of other languages (almost any other languages) dislike VB! :laugh:
It means that problems that should be spotted or at least considered at compilation time don't get caught until runtime, and often not until the app is in production - one of the reasons why VB apps are often considered less reliable than C# or C++ apps for example.

lelouch_vi 2 5-Apr-20 5:17am

I see. I'm really worried about it. I thought I downloaded a visual studio with a bug. So I should really convert that string to an integer to avoid "weak typing" haha. So vb is really assuming that as an integer.
Thank you so much for all your help!

OriginalGriff 5-Apr-20 5:22am

You're welcome!

OriginalGriff 5-Apr-20 5:35am

Or use a class level integer, and update that - then convert it to a string to display in the label.
That also has the advantage of "separating concerns" between the UI (display stuff) and the BL (logic of what happens).

lelouch_vi 2 5-Apr-20 5:01am

I tried to put "haha" instead of "100" as the value of the label to try something and it gives me an exception for error conversion string to double which makes sense. Does this mean that visual studio is treating "100" as an integer?

OriginalGriff 5-Apr-20 5:12am

See above.

lelouch_vi 2 5-Apr-20 5:40am

I have another question. I'm sorry about this. What happens now is that whenever I save the value of the numeric updown control to a database the label should remain the same but after I clicked the save button it increments by 1. I don't know what is really happening here. Let's say I have a value of 50 in my numeric updown control so my label should be 50 also after I clicked save button the label should 50 but it doesn't it became 51.

OriginalGriff 5-Apr-20 6:03am

Now you need to do some debugging.
Run your code in the debugger, and put a breakpoint at the top of the numCategory_ValueChanged method.
Now do your update and save, and watch what happens ... come back when you've tried it and let me know what you think is happening. :)

I can't do this for you - I only have the code for one method in your app - and no access at all to your DB.

lelouch_vi 2 5-Apr-20 6:31am

haha yeah, thanks. I'll be back here once I'm already done my best for this. haha. thank you for your patience.

lelouch_vi 2 · Accepted Answer · 2020-04-05T00:53:00

this is by far my best solution to my own problem. If there are still improvements that are needed please correct me.

VB

Static num As Integer = 100
        Static oldvalue As Integer


        If numCategory.Value > oldvalue Then

            num -= 1

            lblpoints.Text = num.ToString


        ElseIf numCategory.Value < oldvalue Then
            num += 1
                lblpoints.Text = num.ToString


        Else

            lblpoints.Text = ""

        End If

            oldvalue = numCategory.Value

and to clear the value of the numeric updown control without the label being crazy after the method I just discover this:

VB

numCategory.ResetText()

that is the reason why my label incrementing 1 after the method has done its job because I used

VB

numCategory.value = nothing

to clear the numeric control and so it messes with my code.

Thank you OriginalGriff for helping and patience haha.