Redimensioning Arrays

[jack hoxley]

hi all...

using VB6, you could use a system like this:

Dim SomeArray() as Long
Redim SomeArray(90) as long
Redim Preserve SomeArray(900) as long

and you'd be able to change the last dimension.

Technically this still works in VB.Net, but its excruciatingly slow!!! when timing, VB6 was almost 9x faster than VB.Net...

SO, I'm guessing - whats the ".Net way" of resizing/redimensioning arrays?

Jack;

[MrPolite]

Well that's the only way that I know of doing it. None of the other .NET languages support resizing arrays at runtime (as far as I've heard), so I guess that's the reason that it is slow, probably the VB guys has to write some kind of nasty code to make it compatible with .NET
anyways I think that's the only way to do it....

[hellswraith]

I did this, it seems to happen instantly on my computer. I am running on a PII 450 with 196Mb of ram and Windows XP Home.

Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
        Dim myArray(90) As Long
        Dim myTempArray() As Long
        Dim intCount As Integer
        
        'Populate some values into the array.
        For intCount = 0 To 89
            myArray(intCount) = CLng(intCount)
        Next
 
        'To upsize the array bounds
        'First set the temp to the same size as original array.
        ReDim myTempArray(90)
 
        'Copy the original array to the temp.
        myArray.CopyTo(myTempArray, 0)
 
        'Erase original array and redim it.
        Erase myArray
        ReDim myArray(900)
 
        'Copy the temp array back into the original (now upsized) array.
        myTempArray.CopyTo(myArray, 0)
 
        'This just shows when it is done and that the original contents
        'have been copied back.  Also shows that the added 
        'dimensions are initialized to 0.
        MessageBox.Show("Done")
        For intCount = 0 To 110 Step 10
            MessageBox.Show(myArray(intCount).ToString())
        Next
    End Sub

[DevGrp]

If you dont want to redim and array, use an arraylist. You can add and remove from the list dynamically.

[hellswraith]

I believe the arraylist will have more overhead, but I haven't checked it personally.

[Dillinger4]

As far as ive heard an array in .Net must first be dimensioned with Dim. ReDim cannot be used initially. Plus an array cannot grow or lose dimensions, but the size of the existing dimensions can be changed.

[Dillinger4]

Posted by hellswraith
I believe the arraylist will have more overhead, but I haven't checked it personally.

I think that you would be right. An array should run faster since it is a block of computer memory that contains multiple instances of the same data type. Plus you would have to take into account wether an arraylist offers synchronization(thread safety). In Java you usualy get better performance using an ArrayList vs a Vector.

[jack hoxley]

thanks for the replies people

I'll have a look into that temporary-array method and these "arraylist" things...

Jack;