Index was outside the bounds of the array. VB - vb.net

Question

I have been trying to create a program that will find the word the user has clicked on, in a multiline textbox. This procedure is based on the index from the position of the click. The code I implemented:
Public Class Form1
Private Sub TextBox1_MouseDown(sender As Object, e As MouseEventArgs) Handles TextBox1.MouseDown
If e.Clicks = 1 And e.Button = MouseButtons.Left Then
'Try
Dim indexClicked As Integer = TextBox1.GetCharIndexFromPosition(New Point(e.X, e.Y))
Dim ch As Char = TextBox1.Text.Chars(indexClicked)
Dim indexOfWord As Int32
If Not ch = " " Then
Dim wordFound As Boolean
Dim previousCh As Char
Dim previousIndex As Integer = indexClicked
While Not wordFound
previousIndex = previousIndex - 1
previousCh = TextBox1.Text.Chars(previousIndex)
If previousCh = " " Then
indexOfWord = previousIndex + 1
wordFound = True
End If
End While
Else
indexOfWord = indexClicked + 1
End If
Label1.Text = indexClicked & ", " & indexOfWord
Label2.Text = GetWordByIndex(TextBox1.Text, indexOfWord)
' Catch ex As Exception
' Label2.Text = ex.Message
' End Try
End If
End Sub
Public Shared Function GetWordByIndex(input As String, index As Integer) As String
Try
Dim words = input.Split(" ")
If (index < 0) OrElse (index > words.Length - 1) Then
Throw New IndexOutOfRangeException("Index out of range!")
End If
Return words(index)
Catch ex As Exception
'handle the exception your way
Return String.Empty
End Try
End Function
End Class
The problem is that whenever the program reaches the line:
previousCh = TextBox1.Text.Chars(previousIndex)
it exits with :
An unhandled exception of type 'System.IndexOutOfRangeException' occurred in WindowsApplication1.exe
Additional information: Index was outside the bounds of the array.
While the exception is thrown, by hovering over the previousIndex variable visual studio shows me its value: -1.
I think that previousCh = " " condition never gets true, so the program never exits the while loop, which keeps looking for the previous character. At some point int previousIndex gets negative and the program crashes. Why does not the condtion work properly?
What is the problem?
Thank you.

Answer 1

If you do not want to have the user double click like David Wilson suggested (which i would also agree with) then this will get the result you want. It takes into account if the previous character is a line feed or the start of the text, or the next character is a line feed or end of the text as well. You can add to the If to find "," or "." if needed.
Private Sub TextBox1_MouseDown(sender As Object, e As MouseEventArgs) Handles TextBox1.MouseDown
If e.Clicks = 1 And e.Button = MouseButtons.Left Then
Dim startIndex As Integer = TextBox1.SelectionStart
Dim wordStartFound, wordEndFound As Boolean
Dim nextIndex, indexOfStartOfWord, indexOfEndOfWord, lengthOfWord As Integer
If Not startIndex = 0 Then
While Not wordStartFound
startIndex = startIndex - 1
If TextBox1.Text.Chars(startIndex) = " " Then
indexOfStartOfWord = startIndex + 1
wordStartFound = True
ElseIf startIndex = 0 Then
indexOfStartOfWord = startIndex
wordStartFound = True
ElseIf TextBox1.Text.Chars(startIndex) = Chr(10) Then 'Line Feed'
indexOfStartOfWord = startIndex + 1
wordStartFound = True
End If
End While
Else
indexOfStartOfWord = startIndex
End If
nextIndex = startIndex
While Not wordEndFound
nextIndex = nextIndex + 1
If TextBox1.Text.Chars(nextIndex) = " " Then
indexOfEndOfWord = nextIndex
wordEndFound = True
ElseIf nextIndex = TextBox1.TextLength - 1 Then
indexOfEndOfWord = TextBox1.TextLength
wordEndFound = True
ElseIf TextBox1.Text.Chars(nextIndex) = Chr(10) Then 'Line Feed'
indexOfEndOfWord = nextIndex
wordEndFound = True
End If
End While
lengthOfWord = indexOfEndOfWord - indexOfStartOfWord
Label2.Text = TextBox1.Text.Substring(indexOfStartOfWord, lengthOfWord)
End If
End Sub
Also in your function GetWordByIndex you split the input string into an array
Dim words = input.Split(" ")
then you say
If (index < 0) OrElse (index > words.Length - 1) Then
Throw New IndexOutOfRangeException("Index out of range!")
End If
but when you call .length on an array it returns the number of strings (or whatever is in the array) For example if the input was "The big brown fox jumped over the lazy dog", words.length - 1 will return 8. So if your index you pass through is the start of the word "over" it would fall into the Throw New IndexOutOfRangeException("Index out of range!") as the index would be 26 which is obviously greater than 8.
The code i have provided doesn't use the function to find the word but i thought i would mention that anyway.