Update selected Item in Primefaces selectOneMenu from commandButton - jsf

Question

i have a reset Button and want to select a default value
in the selectOneMenu component when the button is pressed.
I tried different posts, but don't get it working.
here is my page:
<?xml version="1.0" encoding="UTF-8"?>
<ui:composition xmlns="http://www.w3.org/1999/xhtml"
xmlns:h="http://java.sun.com/jsf/html"
xmlns:f="http://java.sun.com/jsf/core"
xmlns:ui="http://java.sun.com/jsf/facelets"
xmlns:p="http://primefaces.org/ui"
template="${pageContext.request.contextPath}/templates/default.xhtml">
<ui:define name="content">
<h:form>
<h1>Maschinenverwaltung</h1>
<p:panelGrid id="editMachinePanelGrid" style="margin-top:200px"
rendered="true">
<f:facet name="header">
<p:row>
<p:column colspan="4">Maschinenverwaltung</p:column>
</p:row>
<p:row>
<p:column colspan="4">Maschine</p:column>
</p:row>
</f:facet>
<p:row>
<p:column colspan="2">
<p:commandButton id="createModeButton2" ajax="true" type="reset"
actionListener="#{machineController.setCreateMode('true')}"
value="Neuanlage" update="machineName, deleteMachine" onclick="PF('machineSelector').selectItem(id='noMachine')">
</p:commandButton>
</p:column>
<p:column colspan="2">
<p:spacer></p:spacer>
</p:column>
</p:row>
<p:row></p:row>
<p:row>
<p:column colspan="2">
<p:selectOneMenu id="machineSelector"
value="#{machineController.currentMachine}" required="true"
var="m" effect="puff" converter="MachineConverter">
<f:selectItem itemLabel="Maschine auswählen" itemValue="" id="noMachine"/>
<f:selectItems value="#{machineController.allMachines}"
var="machine" itemLabel="#{machine.name}" itemValue="#{machine}" />
<p:column>
#{m.name}
</p:column>
<p:ajax listener="#{machineController.machineSelected}"
update="machineName">
</p:ajax>
</p:selectOneMenu>
</p:column>
<p:column colspan="2"
rendered="#{machineController.deleteMachineDisabled()}">
<p:spacer></p:spacer>
</p:column>
<p:column rendered="#{!machineController.deleteMachineDisabled()}">
<p:commandButton id="deleteMachine"
action="#{machineController.deleteCurrentMachine()}"
value="löschen"
disabled="#{machineController.deleteMachineDisabled()}"
rendered="#{!machineController.deleteMachineDisabled()}" />
</p:column>
</p:row>
<p:row>
<p:column colspan="2">Maschinenbezeichnung: </p:column>
<p:column colspan="2">
<p:inputText value="#{machineController.currentMachine.name}"
id="machineName"></p:inputText>
</p:column>
</p:row>
<p:row>
<p:column colspan="2">
<p:commandButton value="Speichern" partialSubmit="true"
process="editMachinePanelGrid"
action="#{machineController.saveMachine()}"></p:commandButton>
</p:column>
<p:column colspan="2">
<p:spacer></p:spacer>
</p:column>
</p:row>
</p:panelGrid>
<h:messages id="messages" />
</h:form>
</ui:define>
<ui:define name="title">Maschinenverwaltung</ui:define>
</ui:composition>
I know, that i have to use the selectValue() Method, but don't know
how to address the Parameter to select the value:
<f:selectItem itemLabel="Maschine auswählen" itemValue="" id="noMachine"/>
I am using Primefaces 5.1
best regards
Heiko

Answer 1

To reset the p:selectOneMenu on client side, you may use the client side API:
First set a widget name for you menu like this:
<p:selectOneMenu widgetVar="wv" ... />
Now you may access and set the value of the menu via the client side API easily:
<p:commandButton
onclick="PF('wv').selectValue('');"
/>
Note that the given value in the selectValue-method should be the value defined by the itemValue-attribute of your select item. As it is empty in your case (itemValue="") you may just pass the empty String '' as value, as shown above.
Unrelated:
I guess your select item should have set the attribute noSelectionOption='true' instead of (only) having set the item value to the empty String.