richface 4.3.4 JBoss EAP 6.1

*.xhtml

<rich:extendedDataTable id="table" value="#{UserBean.arl}" var="var0" style="height:300px; width:500px;"

clientRows="0" selection="#{userBean.selection}" selectionMode="single">

*

*

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@ManagedBean

@SessionScoped

public class UserBean implements Serializable, ActionListener{

public Collection<Object> selection ;

public List<tableItem>  arl;

public Collection<Object> getSelection() {

        return selection;

    }

    public void setSelection(Collection<Object> selection) {

        this.selection = selection;

    }

    public synchronized List<tableItem> getArl() {
        if(null==this.arl )
        {
            this.arl=new ArrayList<tableItem>();
            for(int i=0;i<100;i++)
            {
                tableItem it=new tableItem(String.valueOf(i), String.valueOf(i));
                it.setA0(String.valueOf(i));
                this.arl.add(it);
            }
        }
        return this.arl;
    }
    public void setArl(List<tableItem> arl) {
        this.arl = arl;
    }

};

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public class tableItem implements Serializable{

    private static final long serialVersionUID = 5010664822128552977L;

public String a0;

public String a1;

public tableItem() {

    super();

    this.a0 = "**-";

    this.a1 = "**-";

}

public tableItem(String a0, String a1) {

    super();

    this.a0 = a0;

    this.a1 = a1;

}

public String getA0() {

    return a0;

}

public void setA0(String a0) {

    this.a0 = a0;

}

public String getA1() {

    return a1;

}

public void setA1(String a1) {

    this.a1 = a1;

}

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when i select row selection not initial. selection==null. why? help please