Array of Hash Tables

[Glenn Grant via .NET 247]

I am trying to create an Array of type Hash Table. When I try to assign a value to a key in the hash table i get a System.NullReferenceException error.

Here is the code:

Public Function ReadTilesFromFile(ByVal Path As String, Optional ByVal TilesetDir As String = "tilesets/")
Dim i As Integer ' Counter for loops
Dim TilesetPath As String = TilesetDir & Path ' Full path to tileset file
Dim xDS As New Tileset() ' Make xDS point to Tilset
Dim xRow As Tileset.TilesRow ' Make xRow point to Tileset.TilesRow

If New FileInfo(TilesetPath).Exists Then ' If the tileset file exists
xDS.ReadXml(TilesetPath, _
System.Data.XmlReadMode.IgnoreSchema) ' Read tiles table from file

If xDS.Tiles.Rows.Count > 0 Then ' Check if there are rows in the table
For i = 0 To (xDS.Tiles.Rows.Count - 1) ' For each row in the table
xRow = xDS.Tiles.Rows.Item(i) ' Use the current row of the table

ReDim Preserve aryTiles(i)

MsgBox("die")
MsgBox(aryTiles(i).Count)
' AsciiTile
If Not xRow.IsAsciiTileNull() Then ' If there is data in the AsciiTile field
'aryTiles(i).Add("AsciiTile", xRow.AsciiTile) ' Put the data in the Tiles hashtable
aryTiles(i).Item("AsciiTile") = xRow.AsciiTile
End If
MsgBox("die1")
' Image
If Not xRow.IsImageNull() Then ' If there is data in the Image field
aryTiles(i).Add("Image", xRow.Image) ' Put the data in the Tiles hashtable
End If
Next i

End If
Else
TilesetError(1) ' Call TilesetError, MissingTilesetFile
End If
End Function

 

[Cor Ligthert]

Glenn,

I am trying to create an Array of type Hash Table. When I try to assign a
value to a key in the hash table i get a System.NullReferenceException
error.

Then there is probably an error in your program. Did it not tell where it
was or did you debug it so that you could see it?

Cor

 

[Chris Dunaway]

Where in this code is the declaration for the array of hashtables?
Perhaps you posted the wrong section of code by mistake?

 

[Jay B. Harlow [MVP - Outlook]]

Glenn,

I am trying to create an Array of type Hash Table.
When I try to assign a value to a key in the hash table
i get a System.NullReferenceException error.

This normally occurs when you initialize an array without initializing the
elements. Hashtable is a reference type, when you use:

Dim list(10-1) As Hashtable

or:

Dim Preserve list(list.Length + 1)

The elements are initialized to Nothing, you need to initialize the
individual elements to a new Hashtable object, something like:

Dim list(10-1) As Hashtable
For index As Integer = 0 to list.Length - 1
list(index) = New Hashtable
Next

ReDim Preserve list(list.Length)
list(list.Length - 1) = New Hashtable

Hope this helps
Jay

 

[Chris Dunaway]

The elements are initialized to Nothing, you need to initialize the
individual elements to a new Hashtable object, something like:

ReDim Preserve list(list.Length)
list(list.Length - 1) = New Hashtable

Of course, if you are ReDim'ing the array by more than a single
element, you will need to use a loop too:

Dim oldlistlength As Integer = list.length
ReDim Preserve list(newlistlength - 1)
For x As Integer = oldlistlength - 1 To newlistlength - 1
list(x) = New Hashtable
Next

 

[Chris Dunaway]

I think in the For loop, it should be

For x As Integer = oldlistlength To newlistlength-1
'Code
Next

my mistake