Field not found in jasperreports 3.5.3 - jasper-reports

Question

I added a data source to my report in iReport Designer , I then dragged some "Text Field"s from the Report Elements palette to the Detail band and I got an error compiling a jasper report:
net.sf.jasperreports.engine.design.JRValidationException: Report design not valid :
[jrc] 1. Field not found : deviceCostsDTO
even the field is declared:
<field name="deviceCostsDTO" class="com.domain.device.DeviceCostsDTO">
<fieldDescription><![CDATA[actionCostsDTO]]></fieldDescription>
</field>
and used here:
<frame>
<reportElement positionType="Float" x="0" y="155" width="802" height="60" isRemoveLineWhenBlank="true" />
<componentElement>
<reportElement x="0" y="36" width="802" height="24" isRemoveLineWhenBlank="true" />
<jr:list xmlns:jr="http://jasperreports.sourceforge.net/jasperreports/components" xsi:schemaLocation="http://jasperreports.sourceforge.net/jasperreports/components http://jasperreports.sourceforge.net/xsd/components.xsd" printOrder="Vertical">
<datasetRun subDataset="costsPerBeneficiaryDataset" >
<datasetParameter name="P_AC_DTO">
<datasetParameterExpression><![CDATA[$F{deviceCostsDTO}]]></datasetParameterExpression>
</datasetParameter>
<datasetParameter name="DOMAIN_CODE">
<datasetParameterExpression><![CDATA[$F{projectDomain}]]></datasetParameterExpression>
</datasetParameter>
<dataSourceExpression><![CDATA[new net.sf.jasperreports.engine.data.JRBeanCollectionDataSource($F{costsPerBeneficiaryWrappers})]]></dataSourceExpression>
</datasetRun>
<jr:listContents height="24" width="802">
<frame>
<reportElement positionType="Float" x="0" y="0" width="802" height="24" isRemoveLineWhenBlank="true" />
<textField>
<reportElement x="0" y="0" width="69" height="24" />
<box leftPadding="5" rightPadding="5">
<topPen lineWidth="0.5" lineStyle="Solid"/>
<leftPen lineWidth="0.5" lineStyle="Solid"/>
<bottomPen lineWidth="0.5" lineStyle="Solid"/>
<rightPen lineWidth="0.5" lineStyle="Solid"/>
</box>
<textElement verticalAlignment="Middle">
<font fontName="DejaVu Sans" size="8"/>
</textElement>
<textFieldExpression><![CDATA[$F{beneficiaryShortName}]]></textFieldExpression>
</textField>
<textField>
<reportElement x="69" y="0" width="50" height="24" />
<box leftPadding="5" rightPadding="5">
<topPen lineWidth="0.5" lineStyle="Solid"/>
<leftPen lineWidth="0.5" lineStyle="Solid"/>
<bottomPen lineWidth="0.5" lineStyle="Solid"/>
<rightPen lineWidth="0.5" lineStyle="Solid"/>
</box>
<textElement verticalAlignment="Middle">
<font fontName="DejaVu Sans" size="8"/>
</textElement>
<textFieldExpression class="java.lang.Long"><![CDATA[$F{numberOfPersonDays}]]></textFieldExpression>
</textField>
<textField>
<reportElement x="119" y="0" width="50" height="24" />
<box leftPadding="5" rightPadding="5">
<topPen lineWidth="0.5" lineStyle="Solid"/>
<leftPen lineWidth="0.5" lineStyle="Solid"/>
<bottomPen lineWidth="0.5" lineStyle="Solid"/>
<rightPen lineWidth="0.5" lineStyle="Solid"/>
</box>
<textElement verticalAlignment="Middle">
<font fontName="DejaVu Sans" size="8"/>
</textElement>
<textFieldExpression class="java.lang.Long"><![CDATA[((com.domain.device.DeviceCostsDTO)$F{deviceCostsDTO}).getTotalCostPerBeneficiary($F{applicantId})]]></textFieldExpression>
</textField>
</frame>
</jr:listContents>
</jr:list>
</componentElement>
</frame>

Answer 1

You're using this field inside a List. You should declare as a field of the dataset your list is using.
Like this:
<?xml version="1.0" encoding="UTF-8"?>
<jasperReport xmlns="http://jasperreports.sourceforge.net/jasperreports" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://jasperreports.sourceforge.net/jasperreports http://jasperreports.sourceforge.net/xsd/jasperreport.xsd" name="report1" language="groovy" pageWidth="842" pageHeight="595" orientation="Landscape" columnWidth="802" leftMargin="20" rightMargin="20" topMargin="20" bottomMargin="20">
<property name="ireport.zoom" value="1.0"/>
<property name="ireport.x" value="0"/>
<property name="ireport.y" value="0"/>
<subDataset name="testDataset">
<field name="testField" class="java.lang.String"/>
</subDataset>
<background>
<band splitType="Stretch"/>
</background>
<title>
<band height="79" splitType="Stretch"/>
</title>
<pageHeader>
<band height="35" splitType="Stretch"/>
</pageHeader>
<detail>
<band height="20" splitType="Stretch">
<componentElement>
<reportElement x="0" y="0" width="791" height="20"/>
<jr:list xmlns:jr="http://jasperreports.sourceforge.net/jasperreports/components" xsi:schemaLocation="http://jasperreports.sourceforge.net/jasperreports/components http://jasperreports.sourceforge.net/xsd/components.xsd" printOrder="Vertical">
<datasetRun subDataset="testDataset">
<dataSourceExpression><![CDATA[new net.sf.jasperreports.engine.JREmptyDataSource(1)]]></dataSourceExpression>
</datasetRun>
<jr:listContents height="20" width="791">
<textField>
<reportElement x="0" y="0" width="100" height="20"/>
<textElement/>
<textFieldExpression class="java.lang.String"><![CDATA[$F{testField}]]></textFieldExpression>
</textField>
</jr:listContents>
</jr:list>
</componentElement>
</band>
</detail>
<pageFooter>
<band height="54" splitType="Stretch"/>
</pageFooter>
<summary>
<band height="42" splitType="Stretch"/>
</summary>
</jasperReport>