How to get report_count from subreport in iReport

I have a sub report in my main report .

I need to hide a text if sub report returns no rows.

I tried to get the number of records of subreport adding a new variable in main report and setting it as destination variable in return values property of subreport(for rount_count), but when I run the main report, the value of variable is null

Solution

To count the record's in subreport

Define a variable in main report

<variable name="subReportCount" class="java.lang.Integer"/>

When calling subreport set the return parameter to you variable

<subreport>
    <reportElement x="100" y="20" width="400" height="20" uuid="a7a89ebb-54d4-4b6e-8c9f-c107e8a40bbb"/>
    <dataSourceExpression><![CDATA[... your datasource ...]]></dataSourceExpression>
    <returnValue subreportVariable="REPORT_COUNT" toVariable="subReportCount"/>
    <subreportExpression><![CDATA[$P{SUBREPORT_DIR} + "Your_subreport.jasper"]]></subreportExpression>
</subreport>

This variable can now be used in a textField, however you need to be careful since the textField need's to be evaluate at the correct time (after subreport has been executed).

The property on the textField is evaluationTime

Example

<textField evaluationTime="Report" pattern="###0">
    <reportElement positionType="Float" x="300" y="60" width="200" height="20" uuid="125aa2d0-3d4e-4377-bed1-b4531c9142c9"/>
    <textElement textAlignment="Right" verticalAlignment="Middle"/>
    <textFieldExpression><![CDATA[$V{subReportCount}]]></textFieldExpression>
</textField>

Evaluation time:

Auto Evaluation time indicating that each variable participating in the expression should be evaluated at a time decided by the engine.
Band The element will be evaluated at band end.
Column A constant specifying that an expression should be evaluated after each column is filled.
Group A constant specifying that an expression should be evaluated after each group break.
Master Used for elements that are evaluated at the moment the master report ends.
Now A constant specifying that an expression should be evaluated at the exact moment in the filling process when it is encountered.
Page A constant specifying that an expression should be evaluated after each page is filled.
Report A constant specifying that an expression should be evaluated at the end of the filling process.

In general when using subreport

if it is in detail band and is repeated on datasource set evalutationTime="Band"
if it's present only one set evalutationTime="Report"