Problem storing value in array

I want to store value in array, from my database. I am using following code but it return error: "Object reference not set to an instance of an objec开发者_运维百科t."

Code is:

Dim w as integer=0

Do While DsChooseSQsNow.tblChooseSQs.Rows.Count > w
      vrSQsNoChosen(w) = DsChooseSQsNow.tblChooseSQs.Rows(w).Item("QNo")
      vrTotalSQsChosen = vrTotalSQsChosen + 1
      w = w + 1
Loop

Error comes on "vrSQsNoChosen(w) = DsChooseSQsNow.tblChooseSQs.Rows(w).Item("QNo")"

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try to print the value DsChooseSQsNow.tblChooseSQs.Rows(w).Item("QNo")

or debug the code

"Object reference not set to an instance of an object." means Item("QNo") may be null

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There are many reasons why this code fails. I would start checking from:

• Size (and boundings) of vrSQsNoChosen array.
• w value when error occurs (is valid index for vrSQsNoChosen array and Rows collection?).
• Item("QNo") value when error occurs (maybe is null?).

Also -- VB.NET implements += operator so you can write:

  w += 1

instead of:

 w = w + 1