我对 Primefaces 数据表有疑问，尤其是对选择对象。
在我的以下代码中，对于绑定到带有选择的数据表的变量“选定问题”，我总是为空。
jsf如下：
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE html
PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"
"http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml" xml:lang="en" lang="en"
xmlns:h="http://java.sun.com/jsf/html"
xmlns:f="http://java.sun.com/jsf/core"
xmlns:p="http://primefaces.org/ui"
xmlns:ui="http://java.sun.com/jsf/facelets">
<ui:composition template="mainTemplate.xhtml">
<ui:define name="contentTitle">Your Questions</ui:define>
<ui:define name="content">
<h:form id="formAllQuestion">
<p:growl id="allQuestionGrowl" showDetail="true"/>
<p:dataTable id="allQuestionsTable" var="question" value="#{allQuestionBean.allQuestionDataHelper}" paginator="true" rows="10"
selection="#{allQuestionBean.selectedQuestion}" selectionMode="single">
<p:ajax event="rowSelect" listener="#{allQuestionBean.onRowSelect}" update=":formAllQuestion:AnswerToQuestionDialogTable :formAllQuestion:allQuestionGrowl"
oncomplete="questDialog.show()"/>
<p:ajax event="rowUnselect" listener="#{allQuestionBean.onRowUnselect}" update=":formAllQuestion:allQuestionGrowl"/>
<f:facet name="header">Select a Row to display your Question Details</f:facet>
<p:column headerText="QuestionID">
#{question.questionId}
</p:column>
<p:column headerText="Question Name">
#{question.questionName}
</p:column>
<p:column headerText="Question Description">
#{question.questionText}
</p:column>
<p:column headerText="Question Short Description">
#{question.questionShortText}
</p:column>
<p:column headerText="Author">
#{question.professor.profSurename} #{question.professor.profName}
</p:column>
</p:dataTable>
<p:dialog header="Question Details" widgetVar="questionDialog" resizable="true" id="questDialog"
showEffect="fade" hideEffect="fade" modal="true">
<p:dataTable id="AnswerToQuestionDialogTable" var="answer" value="#{allQuestionBean.answers}">
<f:facet name="header">
Hier kommt der QR_Code rein!
#{allQuestionBean.selectedQuestion.questionId} - #{allQuestionBean.selectedQuestion.questionName}
</f:facet>
<p:column headerText="Answer">
<h:outputText value="#{answer.answerText}"/>
</p:column>
<p:column headerText="Counts For this Answer">
<h:outputText value="Bis jetz noch nix!"/>
</p:column>
</p:dataTable>
</p:dialog>
</h:form>
</ui:define>
</ui:composition>
</html>
以及相关的 Bean 类（AllQuestionBean.class）：
@ManagedBean(name = "allQuestionBean")
@ViewScoped
public class AllQuestionBean implements Serializable {
private static final long serialVersionUID = 7038894302985973905L;
@ManagedProperty(value = "#{questionDAO}")
private QuestionDAO questionDAO;
@ManagedProperty(value = "#{profSession.professor}")
private Professor professor;
@ManagedProperty(value = "#{answerDAO}")
private AnswerDAO answerDAO;
@ManagedProperty(value = "#{answeredDAO}")
private AnsweredDAO answeredDAO;
private List<Question> questions;
private Question selectedQuestion;
private List<Answer> answers;
private AllQuestionDataHelper allQuestionDataHelper;
public AllQuestionBean(){
System.out.println("Starting Bean: "+this.getClass().getName());
}
@PostConstruct
public void initVariables(){
questions = questionDAO.readByProfessor(professor);
}
public void onRowSelect(SelectEvent event) {
FacesMessage msg = new FacesMessage("Question Selected", selectedQuestion.getQuestionId()+" -- "+selectedQuestion.getQuestionName());
FacesContext.getCurrentInstance().addMessage(null, msg);
}
public void onRowUnselect(UnselectEvent event) {
FacesMessage msg = new FacesMessage("Question Selected", selectedQuestion.getQuestionId()+" -- "+selectedQuestion.getQuestionName());
FacesContext.getCurrentInstance().addMessage(null, msg);
}
//---GETTER and SETTER
public AllQuestionDataHelper getAllQuestionDataHelper() {
allQuestionDataHelper = new AllQuestionDataHelper(questions);
return allQuestionDataHelper;
}
public void setAllQuestionDataHelper(AllQuestionDataHelper allQuestionDataHelper) {
this.allQuestionDataHelper = allQuestionDataHelper;
}
public QuestionDAO getQuestionDAO() {
return questionDAO;
}
public void setQuestionDAO(QuestionDAO questionDAO) {
this.questionDAO = questionDAO;
}
public Professor getProfessor() {
return professor;
}
public void setProfessor(Professor professor) {
this.professor = professor;
}
public AnswerDAO getAnswerDAO() {
return answerDAO;
}
public void setAnswerDAO(AnswerDAO answerDAO) {
this.answerDAO = answerDAO;
}
public AnsweredDAO getAnsweredDAO() {
return answeredDAO;
}
public void setAnsweredDAO(AnsweredDAO answeredDAO) {
this.answeredDAO = answeredDAO;
}
public List<Question> getQuestions() {
return questions;
}
public void setQuestions(List<Question> questions) {
this.questions = questions;
}
public Question getSelectedQuestion() {
System.out.println("getSelectedQuestion");
return selectedQuestion;
}
public void setSelectedQuestion(Question selectedQuestion) {
System.out.println("Set selected Question: "+selectedQuestion);
this.selectedQuestion = selectedQuestion;
}
public List<Answer> getAnswers() {
answers = answerDAO.getAllAnswersForQuestion(selectedQuestion);
return answers;
}
public void setAnswers(List<Answer> answers) {
this.answers = answers;
}
}
数据模型：
public class AllQuestionDataHelper extends ListDataModel<Question> implements SelectableDataModel<Question> {
public AllQuestionDataHelper() {
}
public AllQuestionDataHelper(List<Question> list) {
super(list);
}
@Override
public Object getRowKey(Question question) {
if(!(question == null)){
System.out.println("Your Questions --> Getting RowKey");
System.out.println("RowKey: "+question);
System.out.println("RowKey: "+question.getQuestionId());
}else{
System.out.println("Warning Row Key is null");
}
return question.getQuestionId();
}
@Override
public Question getRowData(String rowKey) {
System.out.println("Your Questions --> Getting RowData");
System.out.println("RowData: "+rowKey);
List<Question> questionList = (List<Question>) getWrappedData();
for(Question q : questionList){
if(rowKey.equals(q.getQuestionId())){
System.out.println("Returning "+q.getQuestionId());
return q;
}
}
return null;
}
}
我调试了一些运行并提到 AllQuestionBean.class 中的变量“selectedQuestion”从未设置。会说，“onRowSelect”中的事件变量包含一个 NULL 对象。如您所见，*.xhtml 中有两个数据表。第一个将正常加载，没有问题。Bean 的 onClick-Method 应该使用第二个数据表启动一个对话框，但会以一个 Nullpointer 退出。
对于数据表，我遵循 Primefaces 的教程 (http://www.primefaces.org/showcase-labs/ui/datatableRowSelectionInstant.jsf)