Can't calculate sum for a column in iReport 4.6.0+XML datasource
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I've built a report from an XML datasource. I've created two nested groups and I'm trying to calculate sum for a column and put total into deepest group footer band.

I've created a variable to aggregate values and a text field to print that variable out to group's footer band. However I'm getting 0.0 (which is initial value expression for my variable) as column sum for every group.

Let me specify some details:

     - TargetGroup_DURATION: variable that aggregates values from column dur/@val
      - Calculation = Sum
      - Reset type = Group
      - Reset group = Target Group
      - Increment type = Group (I've tried also setting this property to Column, Now, and Auto)
      - Increment group = Target Group
      - Variable expression = NumberFormat.getInstance(new Locale("en", "US")).parse($F{dur/@val}).doubleValue()


    - Text field on TargetGroup footer band
     - Text field expression: $V{TargetGroup_DURATION}
     - Evaluation time: Group (I've tried also Now, Column and Auto)
     - Evaluation group: TargetGroup

As I said, I can't get right results. Does anybody now what's the appropriate values that I have to set in order to get right results?

Thanks in advance.