Question

我正在创建自己的MVP框架，并且我在使用泛型时遇到了麻烦。

我的演示者是这样定义的，内部类包含对子元素的引用，子元素也是通用的演示者：

public abstract class Presenter<TView extends View, TKey extends Key>
{
    protected final HashMap<String, StageInstances<?, ?>>   _stages;

    public <TChildView extends View, TChildKey extends Key> void addStage(Class<Presenter<TChildView, TChildKey>> stage, String name)
    {
        _stages.put(name, new StageInstances<TChildView, TChildKey>(stage));
    }

    // ...

    protected class StageInstances<TChildView extends View, TChildKey extends Key>
    {
        protected Class<Presenter<TChildView, TChildKey>>       _presenter;
        protected HashMap<Key, Presenter<TChildView, TChildKey>>    _instances;

        public StageInstances(Class<Presenter<TChildView, TChildKey>>   presenter)
        {
            _presenter = presenter;
            _instances = new HashMap<Key, Presenter<TChildView, TChildKey>>();
        }

        public Presenter<?, ?> getInstance(Key key)
        {
            if (!_instances.containsKey(key))
            {
                try
                {
                    _instances.put(key, _presenter.newInstance());
                } catch (Exception e)
                {
                    e.printStackTrace();

                    return null;
                }
            }

            return _instances.get(key);
        }
    }
}

我有一个具体的实现

public class ResultsPresenter extends Presenter<ResultsView, Results>

和

public class SearchPresenter extends Presenter<SearchView, StringKey>
{
    // ...

    public void bind()
    {
        addStage(ResultsPresenter.class, "results");
    }
}

其中ResultsView，SearchView扩展View和Results，StringKey实现Key

方法addStage（...）抛出以下编译时错误：

**The method addStage(Class<Presenter<TChildView,TChildKey>>, String) in the type 
Presenter<SearchView,StringKey> is not applicable for the arguments 
(Class<ResultsPresenter>, String)**

非常感谢任何帮助或更好的实践

Answer 1

尝试将方法原型更改为：

public <TChildView extends View, TChildKey extends Key> void addStage(Class<? extends Presenter<TChildView, TChildKey>> stage, String name)

请注意我已将Class<Presenter<TChildView, TChildKey>>更改为Class<? extends Presenter<TChildView, TChildKey>>。这将允许您传递Class of Presenter的子类而不是Presenter本身。

Answer 2

我自己没有尝试过，但出于预感，我会说

addStage(Class<Presenter<TChildView, TChildKey>> stage, String name)

应该是

addStage(Class<Presenter<? extends TChildView,? extends TChildKey>> stage, String name)

首先尝试Alex建议。保持代码更易读，并且比我的更有意义。如果两者都失败了，请将它们合并。

Java方法中的嵌套泛型？

2 个答案: