Thursday, October 11, 2012

Object reference not set to an instance of an object

Object reference not set to an instance of an object


One of the biggest mistakes in programming is not allocate space for an object. We often think of declaring variables, but should always ensure that these variables are created. Or, declare a variable does not create the object. She does an object is of type String, Integer, Double, etc.
The following code illustrates the problem well:

''' <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

        '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
       
    End Sub
End Class



When the code reaches the Msgbox, obviously Msgbox function tries to read the first box of the table, however, is zero. I would add that this table cell is not only zero, it does not exist and does not refer to anything.

Obviously, the example is an array, but the problem would be put on any object. Several solutions exist to control our computer codes. Some work better than others depending on the situation.
But here is a programming method that everyone should do at the beginning, use the try.


        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



Try the function says it very well in English, is to try. Try a code because n, is never sure of the result. Early use functions will try to save you time and money. If you run the code to the try function as written, you would notice that the program does not crash like magic. There is no doubt that this is an example that will lead in to another. You can download the sample source code to try and see my future articles. 




The program I love to use:

Sample Code :

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