Question Problem with Array.IndexOf

Coffer · #1 (**permalink**) 06-26-2009, 2:40 PM

Hello!

I have a tricky little problem. I want to retrieve the index of a current occurence inside an array. I use this code:

Code:

Array.IndexOf(myArray, Request.QueryString("i"))

This code ALWAYS returns 0 even if the array contains 10 indexes... I read somewhere in this thread that Array.IndexOf returns the very first occurence of a value inside the array. Does that mean that Array.IndexOf always should return 0? Since all fields in the array are unique it should return 9 if Request.QueryString("i") equals to a value in the 9th position of the array, right? Or am I thinking wrong?

If I am thinking wrong, how should I retrieve the index of a current request from the array?

// Kristofer

MattP · #2 (**permalink**) 06-26-2009, 4:03 PM

This returns 6 like expected.

Code:

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

		MessageBox.Show(Array.IndexOf(ints, 7))

Coffer · #3 (**permalink**) 06-26-2009, 4:48 PM

To me the problem still occurs. This is the code I am using...

Code:

Dim NewStr As String = ""
Dim Directory As New DirectoryInfo(Request.QueryString("f"))
Dim File As FileInfo

For Each File In Directory.GetFiles("*.jpg")
     NewStr += File.Name.Substring(0, File.Name.Length - 4) & ","
Next

Dim myArray() As String = Split(NewStr.Substring(0, NewStr.Length - 1), ",")

' This is where the error occurs... it ALWAYS returns IndexOf = 0
Dim CurrentIndex As Integer = Array.IndexOf(myArray, Request.QueryString("i")) + 1
lblcuridx.Text = "index of " & Request.QueryString("i") & ".jpg is " & CurrentIndex

What am I doing wrong?

MattP · #4 (**permalink**) 06-26-2009, 5:52 PM

What is Request.QueryString("i") returning?

Array.IndexOf will return -1 if you don't have a match (which you're incrementing by 1)

Example using strings:

Code:

		Dim strings() As String = New String() {"Document1", "Document2", "Document3", "Document4", "Document5"}

		'Returns -1
		MessageBox.Show(Array.IndexOf(strings, "Document10"))

		'Returns 2
		MessageBox.Show(Array.IndexOf(strings, "Document3"))

Coffer · #5 (**permalink**) 06-26-2009, 7:05 PM

The function is used to display a navigational structure for an image gallery. Request.QueryString("i") returns the filename of the image currently displayed on the screen. With this information I can add "previous" and "next" buttons on the page.

Request.QueryString("i") returns the current Filename.

Code:

lblcuridx.Text = "index of " & Request.QueryString("i") & ".jpg is " & CurrentIndex

The code above should (if everything worked as expected) show "index of IMG_0370.jpg is 12 (as the 12th index in the array holds the value IMG_0370).

I have tried to write it as a string of variables as you described. Yet the code returns "0" despite the position in the array...

JohnH · #6 (**permalink**) 06-26-2009, 9:05 PM

The code works as expected, but the search is case-sensitive, could that be why?

Also, this code is better:

Code:

Dim folder As String = Request.QueryString("f")
Dim search As String = Request.QueryString("i")
Dim filenames As New List(Of String)
For Each filepath As String In IO.Directory.GetFiles(folder, "*.jpg")
    filenames.Add(IO.Path.GetFileNameWithoutExtension(filepath))
Next
Dim currentIndex As Integer = filenames.IndexOf(search)

Coffer · #7 (**permalink**) 06-27-2009, 3:49 AM

Finally it works. Thank you so much for the insight about case sensitivity.

Code:

Array.IndexOf(myArray, UCase(strFileName)) + 1

renders the right index of the current image. As a parenthesis I wonder why the usage of this code requires me to remove "+ 1"? It works like a charm, but why does it render the wrong value when I leave "+ 1" there? It doesn't render the wrong value if I just want to present the index on the screen...