Row counter in sub report - Jaspersoft - jasper-reports

Question

I have a subreport that receives two parameters and therefore generates as many reports as there are combinations of parameters, I have to put a row counter in the sub report but this must not reset every report generated by the sub report but must continue the numbering.
This is a conversion from a crystal report
In crystal report do this:
shared numberVar J;
if trim({field}) <> '' then J:=J+1;
I have a subreport to which I pass in the sql query two parameters whose values ​​are generated by the main report, the combination of these parameters in the subreport generates a series of reports in the main report because the subreport is in the detail band.
In the subreport I have to insert a variable that counts the number of rows, but when I insert this variable the numeric counter is reset and starts counting in the new report generated by the subreport, I would like the counter not to reset
Main report
Detail of the band
subreport
Subreport
report 1
1 row
2 rows
3 rows
report 2
1 row
2 rows
3 rows
I would like to have
- report 1
1 row
2 rows
3 rows
-report 2
4 rows
5 rows
6 rows
I hope I was clear
Do you have any ideas?
Can someone help me?
Please
Thanks a lot to everyone

Answer 1

You can pass back and forth a running row count variable to the subreport using parameters and return variables.
You'd need something like this:
(in the master report)
<!-- variable that stores the running row count in the master report -->
<variable name="SubreportRowCount" class="java.lang.Integer" calculation="System">
<initialValueExpression>0</initialValueExpression>
</variable>
...
<subreport>
...
<!-- pass the current value to the subreport -->
<subreportParameter name="InitialRowCount">
<subreportParameterExpression>$V{SubreportRowCount}</subreportParameterExpression>
</subreportParameter>
...
<!-- get back the updated value from the subreport -->
<returnValue subreportVariable="RunningRowCount" toVariable="SubreportRowCount"/>
...
</subreport>
(in the subreport)
<!-- parameter that receives the initial value from the master -->
<parameter name="InitialRowCount" class="java.lang.Integer"/>
...
<!-- running row count variable -->
<variable name="RunningRowCount" class="java.lang.Integer">
<variableExpression>$P{InitialRowCount} + $V{REPORT_COUNT}</variableExpression>
</variable>
...
<!-- show the running count in a text element -->
<textField>
...
<textFieldExpression>$V{RunningRowCount}</textFieldExpression>
</textField>