c# - 如何从 Action() 返回值？

Question

关于这个问题的答案Passing DataContext into Action() , 如何从 action(db) 返回一个值？

SimpleUsing.DoUsing(db => { 
// do whatever with db 
}); 

应该更像是:

MyType myType = SimpleUsing.DoUsing<MyType>(db => { 
// do whatever with db.  query buit using db returns MyType.
}); 

Answer 1

您可以使用 Func<T, TResult> 通用委托(delegate)。 (参见 MSDN )

Func<MyType, ReturnType> func = (db) => { return new MyType(); }

还有一些有用的通用委托(delegate)考虑了返回值:

• Converter<TInput, TOutput> ( MSDN )
• Predicate<TInput> - 总是返回 bool ( MSDN )

---

方法:

public MyType SimpleUsing.DoUsing<MyType>(Func<TInput, MyType> myTypeFactory)

通用委托(delegate):

Func<InputArgumentType, MyType> createInstance = db => return new MyType();

执行:

MyType myTypeInstance = SimpleUsing.DoUsing(
                            createInstance(new InputArgumentType()));

或明确地:

MyType myTypeInstance = SimpleUsing.DoUsing(db => return new MyType());