ActionListener 不能与 ViewScope 一起正常工作？

Question

又是我，

自从使用action 切换到actionListener 后，我遇到了这个问题。这是一个奇怪的麻烦，我不知道为什么会这样。

当我试图从 PrimeFaces 数据表中删除一个项目时，我会得到 NullPointerException。但是，如果我先编辑那个项目然后再回来删除，就可以了！？

我正在使用 actionListener 在 JSF 中使用 Ajax。当我使用动作时，它仍然可以正常工作。

JSF 页面

<p:commandButton id="editButton" icon="ui-icon-pencil"
                 value="#{appBundle.Edit}"
                 action="detail.xhtml?faces-redirect=true">
    <f:setPropertyActionListener value="#{a}"
                                 target="#{academicManagedBean.academicSelected}"/>
</p:commandButton>
<p:commandButton id="deleteButton" icon="ui-icon-trash"
                 value="#{appBundle.Delete}"
                 actionListener="#{academicManagedBean.delete}"
                 update=":growl,datalist">
    <p:confirm header="Confirmation" message="Are you sure?" icon="ui-icon-alert" />
    <f:setPropertyActionListener value="#{a}"
                                 target="#{academicManagedBean.academicSelected}" />
</p:commandButton>
<p:confirmDialog global="true" showEffect="fade" hideEffect="explode">  
    <p:commandButton value="Yes" type="button"
                     styleClass="ui-confirmdialog-yes" icon="ui-icon-check"/>  
    <p:commandButton value="No" type="button"
                     styleClass="ui-confirmdialog-no" icon="ui-icon-close"/>       
</p:confirmDialog>

托管 Bean 类

@ManagedBean
@ViewScoped
public class AcademicManagedBean extends TblAcademic implements Serializable {

    private List<TblAcademic> all;
    private static TblAcademic academicSelected;

    public AcademicManagedBean() {
        super();
    }

    public List<TblAcademic> getAll() {
        try {
            all = new com.rdb.bll.AcademicBLL().getAll();
            return all;
        } catch (Exception ex) {
            Logger.getLogger(AcademicManagedBean.class.getName()).log(Level.SEVERE, null, ex);
            return null;
        }
    }

    public void add(ActionEvent actionEvent) throws Exception {
        boolean check = new com.rdb.bll.AcademicBLL().add(this);
        if (check) {
            JsfUtil.addSuccessMessage("Congratulation, new student has been added successfully!");
        } else {
            JsfUtil.addErrorMessage(ResourceBundle.getBundle("com.rdb.service.AppBundle").getString("PersistenceErrorOccured"));
        }
    }

    public void update(ActionEvent actionEvent) throws Exception {
        boolean check = new com.rdb.bll.AcademicBLL().update(AcademicManagedBean.academicSelected);
        if (check) {
            JsfUtil.addSuccessMessage("Congratulation, student has been updated successfully!");
        } else {
            JsfUtil.addErrorMessage(ResourceBundle.getBundle("com.rdb.service.AppBundle").getString("PersistenceErrorOccured"));
        }
    }

    public void delete(ActionEvent actionEvent) throws Exception {
        boolean check = new com.rdb.bll.AcademicBLL().delete(AcademicManagedBean.academicSelected);
        if (check) {
            JsfUtil.addSuccessMessage("Congratulation, student has been deleted successfully!");
        } else {
            JsfUtil.addErrorMessage(ResourceBundle.getBundle("com.rdb.service.AppBundle").getString("PersistenceErrorOccured"));
        }
    }

    public String studentDetail() {
        TblStudent std = new com.rdb.bll.StudentBLL().getById(AcademicManagedBean.academicSelected.getStudentRollNo());
        new StudentManagedBean().setStudentSelected(std);

        return "/backend/student/detail.xhtml?faces-redirect=true";
    }

    public String getClassNameById(int classId) {
        TblClass objClass = new com.rdb.bll.ClassBLL().getById(classId);
        return objClass.getClassName();
    }

    public TblAcademic getAcademicSelected() {
        return academicSelected;
    }

    public void setAcademicSelected(TblAcademic academicSelected) {
        AcademicManagedBean.academicSelected = academicSelected;
    }

我做错了吗？请帮我改正，谢谢。

Answer 1

<p:commandButton id="deleteButton" icon="ui-icon-trash"
                 value="#{appBundle.Delete}"
                 actionListener="#{academicManagedBean.delete}"
                 update=":growl,datalist">
    <p:confirm header="Confirmation" message="Are you sure?" icon="ui-icon-alert" />
    <f:setPropertyActionListener value="#{a}"
                                 target="#{academicManagedBean.academicSelected}" />
</p:commandButton>

您正在actionListener 方法而不是操作方法中执行删除。这个不对。业务操作应在action 方法中执行。所有操作listeners，包括<f:setPropertyActionListener>,，都在action 方法之前调用，其顺序与在命令组件上声明和分配的顺序完全相同。因此，实际上，首先调用删除，然后设置属性。这就解释了为什么在删除期间该属性为空。

解决方法很简单：使其成为真正的操作方法：

<p:commandButton id="deleteButton" icon="ui-icon-trash"
                 value="#{appBundle.Delete}"
                 action="#{academicManagedBean.delete}"
                 update=":growl,datalist">
    <p:confirm header="Confirmation" message="Are you sure?" icon="ui-icon-alert" />
    <f:setPropertyActionListener value="#{a}"
                                 target="#{academicManagedBean.academicSelected}" />
</p:commandButton>

不要忘记删除 ActionEvent 参数：

public void delete() {  
    // ...
}

本文摘自 JSF Guru Balcus 在此处Posted by JSF Guru 发布的答案