[英]Dynamically instantiate classes extending baseclass using reflection
很長時間以來,我一直在努力尋找一種方法來動態實例化擴展特定基類的所有類(在運行時)。 據我所讀,應該使用Reflection
來完成,不幸的是我還沒有弄清楚該怎么做。
我的項目結構如下:
Library
--|
|
--Vehicle.cs (abstract class)
|
--Car.cs (extending vehicle)
|
--Bike.cs (extending vehicle)
|
--Scooter.cs (extending vehicle)
|
--InstanceService.cs (static class)
|
|
ConsoleApplication
--|
|
--Program.cs
InstanceService類包含一個通用方法,該方法應返回IEnumerable<T>
,該方法包含擴展Vehicle
的實例化類,即Car, Bike & Scooter
。
在嘗試了許多不同的解決方案之后,下面介紹的代碼是InstanceService類的當前狀態,這意味着它主要包含調試工具。
InstanceService.cs
using System;
using System.Collections.Generic;
namespace Library
{
public static class InstanceService<T>
{
//returns instances of all classes of type T
public static IEnumerable<T> GetInstances()
{
var interfaceType = typeof(T);
List<T> list = new List<T>();
Console.WriteLine("Interface type: " + interfaceType.ToString());
var assemblies = AppDomain.CurrentDomain.GetAssemblies();
foreach(var assembly in assemblies)
{
Console.WriteLine("Assembly: " + assembly.ToString());
if (assembly.GetType().IsAbstract)
{
var instance = (T) Activator.CreateInstance(assembly.GetType());
list.Add(instance);
}
}
return list;
}
}
}
我還附加了抽象Vehicle
類的代碼以及其實現之一。
Vehicle.cs
namespace Library
{
public abstract class Vehicle
{
protected float maxSpeedInKmPerHour;
protected float weightInKg;
protected float priceInDkk;
}
}
Car.cs
namespace Library
{
public class Car : Vehicle
{
public Car()
{
this.maxSpeedInKmPerHour = 1200;
this.weightInKg = 45000;
this.priceInDkk = 71000000;
}
}
}
我認為您應該感興趣的方法是IsAssignableFrom
。
此外,如果允許使用LINQ,則使用LINQ可以使代碼更加容易,並且由於您一次創建一個對象,因此我建議使用yield return
。
static IEnumerable<T> GetInstances<T>()
{
var baseType = typeof(T);
var types = AppDomain.CurrentDomain.GetAssemblies()
.SelectMany( a => a.GetTypes() )
.Where
(
t => baseType.IsAssignableFrom(t) //Derives from base
&& !t.IsAbstract //Is not abstract
&& (t.GetConstructor(Type.EmptyTypes) != null) //Has default constructor
);
foreach (var t in types)
{
yield return (T)Activator.CreateInstance(t);
}
}
或者,如果出於某種原因而炫耀,並且您想使用一條語句來做到這一點:
var types = AppDomain.CurrentDomain.GetAssemblies()
.SelectMany( a => a.GetTypes() )
.Where
(
t => typeof(T)IsAssignableFrom(t)
&& !t.IsAbstract
&& (t.GetConstructor(Type.EmptyTypes) != null)
)
.Select
(
t => (T)Activator.CreateInstance(t)
);
該方法適用於可以使用默認構造函數實例化的任何類型。 除非我遺漏了某些東西,否則您的類是從另一個類派生的事實就不重要了。
private T MakeInstance<T>()
{
// the empty Type[] means you are passing nothing to the constructor - which gives
// you the default constructor. If you need to pass in an int to instantiate it, you
// could add int to the Type[]...
ConstructorInfo defaultCtor = typeof(T).GetConstructor(new Type[] { });
// if there is no default constructor, then it will be null, so you must check
if (defaultCtor == null)
throw new Exception("No default constructor");
else
{
T instance = (T)defaultCtor.Invoke(new object[] { }); // again, nothing to pass in. If the constructor needs anything, include it here.
return instance;
}
}
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