[英]How to create and use a generic bean for enums in f:selectItems?
I have generic class with this signature: 我有这个签名的泛型类:
public abstract class EnumListBean<E extends Enum<E>> {
public List<E> getEnumList() {
//implementation details
}
}
Currently I have to define a empty subclass in order to access the enumList property for a concrete generic parameter: 目前,我必须定义一个空子类,以便访问具体泛型参数的enumList属性:
@ManagedBean
@ApplicationScoped
public class ItemRarityBean extends EnumListBean<Item.Rarity>{
}
This makes its possible to access the property eg: 这使得访问该属性成为可能,例如:
<f:selectItems value="#{itemRarityBean.enumList}" var="rarity"
itemLabel="#{rarity.readableName}" itemValue="#{rarity}" />
Im wondering whether one really have to declare a deriving bean but cant access the generic class as bean directly: 我想知道是否真的必须声明一个派生bean但不能直接访问泛型类作为bean:
<f:selectItems value="#{enumListBean<Item.Rarity>.enumList}" var="rarity"
itemLabel="#{rarity.readableName}" itemValue="#{rarity}" />
You can't use generics in EL. 你不能在EL中使用泛型。 EL is a runtime language based on reflection.
EL是一种基于反射的运行时语言。 You know, generics is only available during compiletime, not during runtime.
您知道,泛型仅在编译期间可用,而不是在运行时期间。
For your particular purpose, it's likely easier to use OmniFaces <o:importConstants>
. 出于特定目的,使用OmniFaces
<o:importConstants>
可能更容易。
<o:importConstants type="com.example.Item$Rarity" var="Rarity" />
...
<h:selectOneMenu>
<f:selectItems value="#{Rarity}" />
</h:selectOneMenu>
(the var
attribute is not mandatory, but you'd otherwise need to reference it as #{Item$Rarity}
which is not exactly nicely readable; if your Rarity
enum were a standalone enum and not an inner enum, then you could just use type="com.example.Rarity"
) (
var
属性不是必需的,但你需要引用它作为#{Item$Rarity}
,它不是很好读;如果你的Rarity
枚举是一个独立的枚举而不是内部枚举,那么你可以使用type="com.example.Rarity"
)
It's by design treated as a Map<String, Rarity>
, not a List<Rarity>
or so. 它的设计被视为
Map<String, Rarity>
,而不是List<Rarity>
左右。 So if you intend to access the individual items in the var
attribute of <f:selectItems>
, so that you can access specific enum methods, then you'd need to explicitly iterate over Map#values()
(which would require EL 2.2 support). 因此,如果您打算访问
<f:selectItems>
的var
属性中的各个项目,以便可以访问特定的枚举方法,那么您需要显式迭代Map#values()
(这需要EL 2.2支持) )。
<h:selectOneMenu>
<f:selectItems value="#{Rarity.values()}" var="rarity" itemValue="#{rarity}" itemLabel="#{rarity.readableName}" />
</h:selectOneMenu>
Yes, you have to. 是的,你必须。 Because instantiating abstract classes makes no sense.
因为实例化抽象类没有任何意义。
声明:本站的技术帖子网页,遵循CC BY-SA 4.0协议,如果您需要转载,请注明本站网址或者原文地址。任何问题请咨询:yoyou2525@163.com.