[英]How to create lambdas and add them to actions using reflection
假設在C#中我有一個具有任意數量的Actions
,它可以有任意數量的泛型參數:
public class Container
{
public Action a;
public Action<float> b;
public Action<int, float> c;
// etc...
}
我正在這個類的實例上注冊一些調試lambda,它只打印出action的字段的名稱:
public static void Main()
{
Container container = new Container();
container.a += () => Console.WriteLine("a was called");
container.b += (temp1) => Console.WriteLine("b was called");
container.c += (temp1, temp2) => Console.WriteLine("c was called");
container.a();
container.b(1.5f);
container.c(1, 1.5f);
}
我想使用反射自動創建這些調試lambdas,如下所示:
public static void Main()
{
Container container = new Container();
GenerateDebug(container);
if(container.a != null) container.a();
if(container.b != null) container.b(1.5f);
if(container.c != null) container.c(1, 1.5f);
}
public static void GenerateDebug(Container c)
{
Type t = c.GetType();
FieldInfo[] fields = t.GetFields(BindingFlags.Instance | BindingFlags.Public);
foreach(FieldInfo field in fields)
{
Action callback = () => Console.WriteLine(field.Name + " was called");
Type[] actionArgTypes = field.FieldType.GetGenericArguments();
if(actionArgTypes.Length == 0)
{
Action action = field.GetValue(c) as System.Action;
action += callback;
field.SetValue(c, action);
}
else
{
// 1. Create an Action<T1, T2, ...> object that takes the types in 'actionArgTypes' which wraps the 'callback' action
// 2. Add this new lambda to the current Action<T1, T2, ...> field
}
}
}
我能夠在沒有參數的情況下獲得所需的Action結果 - 上面的代碼確實打印出"a was called"
- 但我不知道如何為泛型做這件事。
我相信我知道我需要做什么,而不是如何:
actionArgTypes
的類型創建Action<T1, T2, ...>
object
,該類型包含對callback
操作的callback
。 我將如何做到這一點,或類似的,以實現添加這樣的調試回調所需的效果?
這是一個使用Expression
s的相當簡單的實現,可以直接使用ILGenerator
,但在這種情況下這不值得麻煩。
public static void GenerateDebug(Container c)
{
Type t = c.GetType();
FieldInfo[] fields = t.GetFields(BindingFlags.Instance | BindingFlags.Public);
foreach(FieldInfo field in fields)
{
var fieldName = field.Name;
Type[] actionArgTypes = field.FieldType.GetGenericArguments();
// Create paramter expression for each argument
var parameters = actionArgTypes.Select(Expression.Parameter).ToArray();
// Create method call expression with a constant argument
var writeLineCall = Expression.Call(typeof(Console).GetMethod("WriteLine", new [] {typeof(string)}), Expression.Constant(fieldName + " was called"));
// Create and compile lambda using the fields type
var lambda = Expression.Lambda(field.FieldType, writeLineCall, parameters);
var @delegate = lambda.Compile();
var action = field.GetValue(c) as Delegate;
// Combine and set delegates
action = Delegate.Combine(action, @delegate);
field.SetValue(c, action);
}
}
這是使用ILGenerator
的相同功能,它應該與.net framework 2.0+以及.net core一起使用。 在現實生活中,應該有檢查,緩存,可能還有整個裝配架:
public static void GenerateDebug(Container c)
{
Type t = c.GetType();
FieldInfo[] fields = t.GetFields(BindingFlags.Instance | BindingFlags.Public);
foreach(FieldInfo field in fields)
{
var fieldName = field.Name;
Type[] actionArgTypes = field.FieldType.GetGenericArguments();
var dm = new DynamicMethod(fieldName, typeof(void), actionArgTypes);
var il = dm.GetILGenerator();
il.Emit(OpCodes.Ldstr, fieldName + " was called using ilgen");
il.Emit(OpCodes.Call, typeof(Console).GetMethod("WriteLine", new [] {typeof(string)}));
il.Emit(OpCodes.Ret);
var @delegate = dm.CreateDelegate(field.FieldType);
var action = field.GetValue(c) as Delegate;
// Combine and set delegates
action = Delegate.Combine(action, @delegate);
field.SetValue(c, action);
}
}
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