Passing variable from subreport to main report for conditional styling

Problem Description

If you are trying to pass a variable from a subreport to the main report and try to use it to trigger conditional styling, e.g. border line width.

It may not work because of evaluation time of the script variable.  If you hard code the local variable, or get a value from a query field, it should work.

Here is an example that does not work:

    <style name="Style1" isBlankWhenNull="false">
        <box>
            <pen lineWidth="6.25"/>
            <topPen lineWidth="6.25" lineStyle="Solid" lineColor="#000000"/>
            <leftPen lineWidth="6.25" lineStyle="Solid" lineColor="#000000"/>
            <bottomPen lineWidth="6.25" lineStyle="Solid" lineColor="#000000"/>
            <rightPen lineWidth="6.25" lineStyle="Solid" lineColor="#000000"/>
        </box>
        <conditionalStyle>
            <conditionExpression><![CDATA[$V{sxROW_COUNT} == 88]]></conditionExpression>
            <style radius="0" isBlankWhenNull="true">
                <box>
                    <pen lineWidth="1.25"/>
                    <topPen lineWidth="1.25" lineStyle="Solid" lineColor="#000000"/>
                    <leftPen lineWidth="1.25" lineStyle="Solid" lineColor="#000000"/>
                    <bottomPen lineWidth="1.25" lineStyle="Solid" lineColor="#000000"/>
                    <rightPen lineWidth="1.25" lineStyle="Solid" lineColor="#000000"/>
                </box>
            </style>
        </conditionalStyle>
    </style>

    <variable name="sxROW_COUNT" class="java.lang.Integer">
        <variableExpression><![CDATA[]]></variableExpression>
    </variable>

<returnValue subreportVariable="sxROW_COUNT" toVariable="sxROW_COUNT"/>

Workaround:

You might want to by pass conditional styling and change the property directly, e.g.

   <style name="Style1" isBlankWhenNull="false">
        <box>
            <pen lineStyle="Solid" lineColor="#000000"/>
        </box>
    </style>

<textField evaluationTime="Report">
    <reportElement style="Style1" x="0" y="0" width="817" height="10" stretchType="ElementGroupHeight">
        <propertyExpression name="net.sf.jasperreports.style.box.pen.lineWidth">IF(EQUALS($V{sxROW_COUNT}, 88), "1.25", "6.25")</propertyExpression>
    </reportElement>
    <textElement>
        <font size="5"/>
    </textElement>
    <textFieldExpression>""</textFieldExpression>
</textField>

Caveat: 

This workaround may not work for other output formats than PDF.   Furthermore, there may be more complications for reports with multiple pages.