Revision #3

Index was out of range. Must be non-negative and less than the size of the collection.
Parameter name: index

The error message couldn't do a better job in conveying what went wrong. Lets back up...

An index is an integer that identifies the location of an element in a array, list, or other collection type. When accessing items in an array, list or other collection type, you use parenthesis with an index number inside. Array(Index# or Integer Variable).

What is the range?

• Inclusive Lower Bound
  
  • The Lower Bound is the lowest available index number in the collection, and should always be zero.
    • There will not be a zero index in the collection if there are no items in the collection.
• Inclusive Upper Bound
  • The Upper Bound is the highest available index number in the collection.
• What do you mean by Inclusive?
  • This means that this number is included in the range.
    • Example:
    • Lets say your lowerbound is zero(it always is)
    • Lets say your upperbound is 10
    • This means there would be 11 Items total located at the following indexes:
    • 0,1,2,3,4,5,6,7,8,9,10

Why does the 'Index was out of range.' error occur?

Remember, this error message does an excellent job of conveying what went wrong and what to avoid! It tells you:

• The index must be non-negative, which means the lowest possible index number that can exist is zero.
• The index number that you are using must be smaller than the size of the collection. 
  • Example
  • If the collection contains a total of 6 elements, since the first index in the collection will be zero, instead of 1, this means that you will never have an index of six(otherwise there would be 7 elements in the collection). Therefore the UpperBound of the collection is calculated like this                           UpperBound = Collection.Items.Count - 1, or UpperBound = UBound(Array)

• That's it, just make sure that you are calculating your indexes correctly.

How to avoid this error:

• Always check what the UpperBound(highest available index) of that particular collection is.
• Only attempt to access that index once you have confirmed that it exists
  • Example
  • Option Strict On

    Public Class Form1

        Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click

            Dim MyArray As Integer() = {1, 2, 3, 4, 5, 6, 7, 8, 9, 10}

            Dim Tmp As Integer

            For I = 0 To UBound(MyArray)

                'This will not go outside of the bounds of the array

                'no error will be caught here

                Try

                    Tmp = MyArray(I)

                Catch ex As Exception

                    MsgBox(ex.Message)

                End Try

            Next

            For I = 0 To MyArray.Count - 1

                'This will not go outside of the bounds of the array

                'no error will be caught here

                Try

                    Tmp = MyArray(I)

                Catch ex As Exception

                    MsgBox(ex.Message)

                End Try

            Next

            For I = 0 To 9

                'This will not go outside of the bounds of the array

                'no error will be caught here

                Try

                    Tmp = MyArray(I)

                Catch ex As Exception

                    MsgBox(ex.Message)

                End Try

            Next

            For I = 0 To MyArray.Count - 1

                'This will not go outside of the bounds of the array

                'no error will be caught here

                Try

                    Tmp = MyArray(I)

                Catch ex As Exception

                    MsgBox(ex.Message)

                End Try

            Next

            For I = 0 To MyArray.Count

                'This will go outside of the bounds of the array

                'and an error will be caught

                Try

                    Tmp = MyArray(I)

                Catch ex As Exception

                    MsgBox(ex.Message)

                End Try

            Next

            For I = 0 To 10

                'This will go outside of the bounds of the array

                'and an error will be caught

                Try

                    Tmp = MyArray(I)

                Catch ex As Exception

                    MsgBox(ex.Message)

                End Try

            Next

        End Sub

    End Class

References

• ArgumentOutOfRangeException - ArgumentOutOfRangeException Class
• MSDN - MSDN Website
• MSDN Forums

I hope you find this helpful, and if I have missed something, please update the article!