我希望创建一个PresenterFactory,显然对创建演示者实例负责。
基于此问题中提供的代码示例:
和@ Pacane的回答,我以为我会这样:
PresenterFactoryTests
[TestClass]
public class PresenterFactoryTests {
[TestClass]
public class Instance : PresenterFactoryTests {
[TestMethod]
public void ReturnsInstantialized() {
// arrange
Type expected = typeof(PresenterFactory);
// act
PresenterFactory actual = PresenterFactory.Instance;
// assert
Assert.IsNotNull(actual);
Assert.IsInstanceOfType(actual, expected);
}
[TestMethod]
public void ReturnsSame() {
// arrange
PresenterFactory expected = PresenterFactory.Instance;
// act
PresenterFactory actual = PresenterFactory.Instance;
// assert
Assert.AreSame(expected, actual);
}
}
[TestClass]
public class Create : PresenterFactoryTests {
[TestMethod]
public void ReturnsAuthenticationPresenter {
// arrange
Type expected = typeof(IAuthenticationPresenter);
// act
IAuthenticationPresenter actual =
PresenterFactory
.Instance
.Create<IAuthenticationPresenter, IAuthenticationView>(
new MembershipService());
// assert
Assert.IsInstanceOfType(actual, expected);
}
// Other tests here...
}
}
PresenterFactory
public sealed PresenterFactory {
private PresenterFactory() { }
public static PresenterFactory Instance { get { return getInstance(); } }
P Create<P, V>(params object[] args) where P : IPresenter<V> where V : IView {
V view = (V)Activator.CreateInstance<V>();
return Activator.CreateInstance(typeof(P), view, args);
}
private static PresenterFactory getInstance() {
if (instance == null) instance = new PresenterFactory();
return instance;
}
private static PersenterFactory instance;
}
ApplicationPresenter
public class ApplicationPresenter : Presenter<IApplicationView>, IApplicationPresenter {
public ApplicationPresenter(IApplicationView view, PresenterFactory presenters)
: base (view) {
Presenters = presenters;
// other initializing stuff here...
}
}
但是,由于类型限制,似乎我无法按照上述测试中的规定这样做。
在我的PresenterFactoryTests.Create.ReturnsAuthenticationPresenter
测试方法中,当我使用接口作为类型参数时,它会编译并抛出运行时,因为Activator.CreateInstance
无法创建接口的实例。
除此之外,如果我输入具体类型,它会抱怨它不能明确地将类型转换为我的类型约束,尽管它们都实现了给定的接口。
PresenterFactory
需要ApplicationPresenter
,我将通过其构造函数注入它,以便应用程序可以根据用户要求的功能实例化所有可用的演示者。
我错过了什么?
答案 0 :(得分:2)
我认为你需要一个更通用的参数 - 具体的视图类型,因为你需要2个具体的类型(视图和演示者能够创建它们)和视图的界面类型:
P Create<P, V, IV>(params object[] args)
where P : IPresenter<V> where V :IV, IV: IView {