Handle Your errors already...

**NextGen1** · 01-05-2010

Deal with your Errors!

I have been browsing around the forums (mpg.net, so many new developers there...) and have come across a lot of programs (most) developed (you can tell) by a new developer, When I run (some of) these programs
I tend to get errors ( A Huge! pet peeve of mine), So I Have taken some time and decided to write a Article (or a Tut of sorts) on how to handle these errors..

Error Types:

Syntax Error (design error)

These errors happen when vb.net doesn't understand what you are telling the code to do. These are easy to Find in VB.NET, because you get a very annoying blue wavy line underneath the issue (don't ignore these...)

Runtime errors

This error happens when your program is running. This can happen when your code is trying to do something it "shouldn't be doing" , I personally hate getting a runtime error when testing someone else's software for them. How can you get this error? Writing to a file that doesn't exist , opening a file that doesn't exist and so forth. It's your job as the programmer to plan ahead and determine how you can handle this (Such as using FileOpenDialog)

Logic errors

Logic Errors occur when the result (or part of the code) landed an answer you didn't expect.

How to handle (Debug Like Hell)

Lets first start by learning how to deal and prevent Syntax errors (or design errors)

Note: (For screenshot purposes I have created a blank project, I have added no controls and I am viewing code for Form1)

[IMG]https://i111.photobucke*****m/albums/n121/golmor/textboxerrorsyn.jpg[/IMG]

Note: Those Who C&P will have this problem a lot, because when you copy and paste a code without adding the components, you will receive a designer error.

Solution: Hover your mouse over the blue wavy line, in this case you will get a "Tip" saying "Declaration Expected" In this case, simply add a texbox to the form, be sure the name you have given (or copied.............) matches the name of the component.

In some cases you will need to use dim to be sure it is declared (if that is the reason)

let’s use this sample code.

Code:

gettext = textbox9.text

Let’s say textbox9 is a real component on the form (right name and all) and gettext was underlined, what would you do ?

There is a right way and a wrong way to use dim (I'll touch on it briefly, but I know I seen a tut out here on mpgh.net that goes into details about dim)

[IMG]https://i111.photobucke*****m/albums/n121/golmor/dim123.jpg[/IMG]

What is wrong with the code? Take a second and try to figure it out before moving down...
.
.
Answer = Dim should be place above the the code to be declared, and also must be placed ( Also learn Public and Private, if you want a tut on that, PM me) and when you use dim, you may need to declare it "as" something. (In this case, I’m using string)

The code should be

Code:

Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load

        Dim gettext as string

        gettext = "designer"
        TextBox9.Text = gettext

        
    End Sub

Final Screenshot, Don't ignore these either

[IMG]https://i111.photobucke*****m/albums/n121/golmor/errorlist.jpg[/IMG]

Note: You can publish with designer errors, so don't ignore them.

Runtime Errors:

Ever debug your application and get a error message mid code, or mid process, that’s a runtime error, a error that happens in code while it is (as name implies...Running!)

I’m going to use the (with Rnd() and Cases and Num and clnt () being so common among new learners) overflow error

[IMG]https://i111.photobucke*****m/albums/n121/golmor/Overflow.gif[/IMG]

Note: If you try and divide by 0 you will get an overflow, if you create a random number between 1-6 in order to generate a random response via case and the number is
not a "possible case" you will get a overflow.

Note: Deal with runtime errors as they occur, Do not overlook these, even if a debug shows up clean, reason being... Your user may stumble upon this part of the code (where maybe you overlooked it, and this happens a lot, the program will (almost) always crash.

Note: if you ever thing a mathematical equation can result in zero use + 1

Example of + 1 and when to use it, let’s say you do

Code:

dim r 
r = rnd() * 4

ask yourself before you continue , is it possible to land a 0 result (null) , the answer is yes, 0(can be the random number) * 4 = 0, this may never happen to you
during debugging, but may happen to a user

your code should be ( to prevent this)

[code]
dim r
r = rnd() * 4 + 1
[code]

Now if the code lands a 0 , it will add 1 , and the result will = 1

How to "trap" in order to deal with runtime errors

VB.NET has a class that deals with runtime errors. "Exception"

Note: We use try to catch runtime errors and determine the appropriate action to deal with them.

Code:

Try
' to do something
msgbox "all is ok"

Catch ex As Exception

msgbox (ex.message) 'Displays a message box with the error..like "resulted in 0" or "File not found"

End Try

or the cleanup method (which is optimal according to msdn, however , it's a life saver to me)

Use Finally, which will work out the cleanup and allow a action to continue regardless of an error

Code:

Try

Catch ex As Exception

Finally

End Try

If you know what is causing the error you can use try to add different handlers.

Code:

Try
' something

Catch ex As Exception
' msgbox (ex.message)

Catch ex As System.IO.FileNotFoundException ' for file not found

msgbox (ex.message) ' or anything you like

End Try

Logic errors

Try this, open vb.net, copy and paste this code (add a textbox)

Code:

'do this in form load for simplicity

Dim a As Integer
Dim b As Integer
Dim total As Integer

a = 5.5
b = 3
total = x * y
TextBox1.Text = total

You would assume the answer would be 16.5, but you may be surprised, the answer is 16!!!!..!!!

Logic errors are hard to find, program doesn’t crash, so... not runtime, no wavy blue wavy lines, so...not a syntax error, so what do we do to fix the problem, in this case.... lots and lots of debugging and breakpoints.

Adding a breakpoint is as simple as click next to a line of code on the grey area to the right, what this will do is (in a sense) Pause the code at a particular part of the code (chosen)

[IMG]https://i111.photobucke*****m/albums/n121/golmor/break1.jpg[/IMG]

Run your application, when the program hits your breakpoint your application will "break" (pause) hover over the breakpoint (highlighted, image below) you will notice some details, use those details to determine any issues you may be having, (debugging)

Press F10 on your keyboard to step through one line at a time, being sure to look for any inconsistencies .

......................................

Ok , that's my error handling article , Use it, Keep your code clean.