Calculate total of a column of list in Jasper Report

Question

In JasperReport, I have a list with all the orders of a customer, for every customer. I would like to calculate the total of all the items' prices in every list.

This is my list:

<jr:list>
    <datasetRun subDataset="listDataset">
    <dataSourceExpression><![CDATA[new net.sf.jasperreports.engine.data.JRBeanCollectionDataSource($F{products})]]>  </dataSourceExpression>
    </datasetRun>
    <jr:listContents height="20">
       <textField>
        <reportElement style="table_TD" x="100" y="0" width="100" height="20"/>
        <textElement/>
        <textFieldExpression class="java.lang.String"><![CDATA[$F{color}]]></textFieldExpression>
    </textField>
    <textField>
        <reportElement style="table_TD" x="0" y="0" width="100" height="20"/>
        <textElement/>
        <textFieldExpression class="java.lang.Integer"><![CDATA[$F{articleNo}]]></textFieldExpression>
    </textField>
    <textField>
        <reportElement style="table_TD" x="200" y="0" width="100" height="20"/>
        <textElement/>
        <textFieldExpression class="java.lang.Double"><![CDATA[$F{price}]]></textFieldExpression>
    </textField>
</jr:listContents>

The sub-dataset I use to fill it (I use a JRBeanCollectionDataSource for the whole report):

<subDataset name="listDataset">
        <field name="color" class="java.lang.String"/>
        <field name="articleNo" class="java.lang.Integer"/>
        <field name="price" class="java.lang.Double"/>

    </subDataset>

In the master report I defined a variable with the subdataset's field "price" as expression:

<variable name="totalPrice" class="java.lang.Double"calculation="Sum">
        <variableExpression><![CDATA[$F{price}]]></variableExpression>
    </variable>

But this is always null. If I define the same variable in the list's dataset, the total is calculated correctly, but I cannot use it in the master report.

So my question is: Is there any way I can achieve this with a list? Or do I have to use a subreport (because it can return a value)?