Switch类有什么用? [英] What are Switch classes used for?

问题描述

什么是开关类(从 org.eclipse.emf.ecore.util.Switch< T> 派生)?

What are switch classes (derived from org.eclipse.emf.ecore.util.Switch<T>) used for?

javadoc 解释为

所有开关类的抽象基类.

An abstract base class for all switch classes.

这无济于事，因为我以前从未听说过开关类".

which does not help as I have never heared about "switch classes" before.

推荐答案

switch类是允许您基于模型对象(在这种情况下为EMF模型对象)选择和实例化类型的具体实例的类.).我所看到的示例表明，它对于为EMF模型实例化类型特定的适配器很有用.

A switch class is a class that allows you to choose and instantiates a concrete instance of a type based on a model object (in this case, an EMF model object). The examples I've seen suggest it's useful for instantiating type-specific adapters for an EMF model.

您可以通过重写doSwitch方法来使用它.例如，假设我有一个模型对象，并且我想实例化一个与我模型中的 type 值相对应的适配器对象:

You use it by overriding the doSwitch method. For instance, say I've got a model object, and I want to instantiate an adapter object that corresponds to the type value in my model:

public class ExampleSwitch extends Switch<Adapter> {

    public Adapter doSwitch(EObject eobject) {
        if (eobject instanceof MyModel) {
            switch (eobject.getType()) {
                case TYPEA:
                    Adapter result = createTypeAAdapter(eobject);
                    if (result == null) {
                        return createDefaultAdapter(eobject);
                    }
                    return result;
                case TYPEB:
                    ...
                default:
            }
        }
    } 
}

eclipse org.eclipse.emf.common.notify.AdapterFactory然后将使用它返回一个适配器.

An eclipse org.eclipse.emf.common.notify.AdapterFactory would then use this to return an Adapter.

public class MyAdapterFactory implements AdapterFactory {
    public boolean isFactoryForType(Object o) {
        return (o instanceof MyModel);
    }
    public Adapter adapt(Notifier notifier, Object type) {
        return mySwitch.doSwitch((EObject)notifier);
    }
}  

我已从此处.我尚未对此进行验证，但是显然EMF​​生成器可以选择为您生成AdapterFactories和Switch类.

I've pulled this information from here. I haven't verified this, but apparently the EMF generator can optionally generate your AdapterFactories and Switch classes for you.

这篇关于Switch类有什么用?的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！