Object reference not set to an instance of an object (part 2)
In a previous article, I demonstrated a simple and common error in programming: not create an object (or element).
When running the computer code, an error "fatal" occurs and the program stops. To solve the problem, I have not corrected, but I have rather isolated.
Here is an overview of the code from the previous article:
''' <summary> ''' crash test and how to improve your coding ''' </summary> ''' <remarks></remarks> Public Class Form1 Private Sub Form1_Load(sender As System.Object, e As System.EventArgs) Handles MyBase.Load End Sub ''' <summary> ''' pressing button1 will crash he program ''' this crash is the typical crashing type for all beginners ''' </summary> ''' <param name="sender"></param> ''' <param name="e"></param> ''' <remarks></remarks> Private Sub Button1_Click(sender As System.Object, e As System.EventArgs) Handles Button1.Click Dim aString() As String 'declare and array only Try 'a crash will occur and the code won't be able to handle it MsgBox(aString(0)) ' you do something with the array and and array is nothing Catch ex As Exception End Try End Sub End Class |
The function Try without a following error might occur:
Thus, the function Try isolates and captures the error preventing some way to stop whole the program. Keep in mind that Try do not correct the problem really. Indeed, the error in this case is an array is declared without assigning memory space for strings. A rookie mistake but also for the more experienced simply by accident.
But it was possible that the function Try detects an error may prevent the user. That is to say, prevent the user program so that it can then inform the designer of the computer code of the situation. Would this be the beginning of a quality control?
The answer to the question is yes. Yes, it is possible to capture the error. Yes the catch function which in French means attraper .
I don�t want to make a big this article too long. I invite you to do this: add a Msgbox after the catch line.
Try 'a crash will occur and the code won't be able to handle it MsgBox(aString(0)) ' you do something with the array and and array is nothing Catch ex As Exception MsgBox(ex.Message) 'add basic error message here End Try |
When you execute the code, instead of crashing the entire program, at least it will display a "controlled" message and finish the function.
� propos
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