使用 findComponent 方法获取 Null？

Question

这是我添加的 Java 代码

 public void collapseTreeById(ActionEvent event) throws IOException {  
        String treeId = FacesContext.getCurrentInstance().getExternalContext().getRequestParameterMap().get("treeId");  
        UIViewRoot viewRoot = FacesContext.getCurrentInstance().getViewRoot();  
        UITree tree = (UITree)viewRoot.findComponent(treeId);  
        tree.setToggleType(SwitchType.server);;  
        }

和jsf页面变化

<a4j:commandLink actionListener="#{inventoriesBean.collapseTreeById}"
                                value="collapse" render="treeServType">
                                <f:param value="treeServType" name="treeId" />
                            </a4j:commandLink>

但是我在这一行中得到 Null UITree tree = (UITree)viewRoot.findComponent(treeId);

这里treeServType是树

的id

Answer 1

那么简单的意思就是给定findComponentsearch expression does not exist in the component tree. You seem to have passed the sole component ID and you are searching inside UIViewRoot (the root of the component tree). This will fail if the target component is by itself actually inside a NamingContainer分量的分量，比如<h:form>.

如果您不能或不想更改 findComponent 搜索表达式来表示像 formId:treeId 这样的绝对组件 ID，并且它具有与 NamingContainer 相同的父级该命令 link，那么您应该通过该命名容器父项进行搜索。

String treeId = FacesContext.getCurrentInstance().getExternalContext().getRequestParameterMap().get("treeId");  
UIComponent namingContainerParent = event.getComponent().getNamingContainer(); 
UITree tree = (UITree) namingContainerParent.findComponent(treeId); 
// ...

使用 findComponent 方法获取 Null？

Getting Null with findComponent method?

jsf

jsf-2