[英]How to pass an object type to call a generic method
我的通用方法是這樣
public static class AppContainerInstaller
{
public static IMessageHandler<T> Resolve<T>()
{
return _container.Resolve<IMessageHandler<T>>();
}
}
我試圖從另一個類中調用此通用方法
public static string ProcessMessage(IMessage message)
{
messageHandler = AppContainerInstaller.Resolve<message.GetType()>();
// THe previous line throws an error.
return messageHandler.Handle(message);
}
誰能告訴我如何將消息類型傳遞給通用方法?
您必須這樣做:
messageHandler = AppContainerInstaller.Resolve<IMessage>();
Resolve
方法是應該在T中傳遞類型的方法。您看到,使用泛型時,必須提供一個實際的類型。您可能想更改Resolve
以獲取T參數,以便傳遞message
。 像這樣:
public static IMessageHandler<T> Resolve<T>(T param)
您這樣稱呼它:
messageHandler = AppContainerInstaller.Resolve<IMessage>(message);
有兩種獲取運行時類型的方法:將消息作為參數傳遞或使用反射。
修改方法:
public static IMessageHandler<T> Resolve<T>(T unused)
{
return _container.Resolve<IMessageHandler<T>>();
}
這將允許運行時類型查找:
// Cast to dynamic to force runtime type
messageHandler = AppContainerInstaller.Resolve((dynamic) message);
您也可以使用反射,盡管這會降低性能。
private static readonly MethodInfo ResolveMethodInfo
= typeof(AppContainerInstaller).GetMethod("Resolve", BindingFlags.Public | BindingFlags.Static);
// Assuming there exists a non-generic interface IMessageHandler
private readonly ConcurrentDictionary<Type, Func<IMessageHandler>> _methodCache
= new ConcurrentDictionary<Type, Func<IMessageHandler>>();
public static string ProcessMessage(IMessage message)
{
messageHandler = Resolve(message.GetType());
return messageHandler.Handle(message);
}
private IMessageHandler Resolve(Type type)
{
// Cache the generated method to avoid repeated reflection penalty.
var resolve = _methodCache.GetOrAdd(type, () => ResolveMethodInfo.MakeGenericMethod(type));
return resolve();
}
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