如何查找使用強類型反射的泛型類方法的MethodInfo？

Question

我想從一個只有在運行時才知道類型參數的泛型類中獲得方法的MethodInfo。

這是我如何會得到MethodInfo爲一個通用的方法從非通用類：

class MyClass 
{ 
    public void MyMethod<T> (T arg) 
    { 
    } 
} 

static MethodInfo Resolve (Type type) 
{ 
    Expression<Action<MyClass, object>> lambda = (c, a) => c.MyMethod (a); 
    MethodCallExpression    call = lambda.Body as MethodCallExpression; 

    return call 
     .Method      // Get MethodInfo for MyClass.MyMethod<object> 
     .GetGenericMethodDefinition() // Get MethodInfo for MyClass.MyMethod<> 
     .MakeGenericMethod (type);  // Get MethodInfo for MyClass.MyMethod<int> 
} 

Resolve (typeof (int)).Invoke (new MyClass(), new object[] {3}); 

現在，如果我想嘗試用一個通用類類似的東西：

class MyClass<T> 
{ 
    public void MyMethod (T arg) 
    { 
    } 
} 

static MethodInfo Resolve (Type type) 
{ 
    Expression<Action<MyClass<object>, object>> lambda = (c, a) => c.MyMethod (a); 
    MethodCallExpression      call = lambda.Body as MethodCallExpression; 

    return call 
     .Method    // Get MethodInfo for MyClass<object>.MyMethod 
     .SomeMagicMethod(); // FIXME: how can I get a MethodInfo 
          // for MyClass<T>.MyMethod where typeof (T) == type? 
} 

Resolve (typeof (string)).Invoke (new MyClass<string>(), new object[] {"Hello, World!"}); 

可能嗎？

Answer 1

public class MyClass<T> 
{ 
    public void MyMethod(T arg, bool flag) 
    { 
     Console.WriteLine("type: MyClass<{0}>, arg: {1}, flag:{2}", typeof(T), 
      arg.ToString(), flag); 
    } 
    public void MyMethod(T arg) 
    { 
     Console.WriteLine("type: MyClass<{0}>, arg: {1}", typeof(T), arg.ToString()); 
    } 
} 
public class GenericInvokeTest 
{ 
    static MethodInfo Resolve(Type type) 
    { 
     var name = ActionName<object>(x => (o) => x.MyMethod(o)); 
     var genericType = typeof(MyClass<>).MakeGenericType(new[] { type }); 
     MethodInfo genericTypeMyMethodInfo = genericType.GetMethod(name); // "MyMethod"); 
     genericTypeMyMethodInfo = genericType.GetMethod(name, new[] { type, typeof(bool) }); 
     return genericTypeMyMethodInfo; 
    } 
    public static void Test1() 
    { 
     Resolve(typeof(string)) 
      .Invoke(new MyClass<string>(), new object[] { "Hello, World!", true }); 
     // Resolve(typeof(string)) 
      .Invoke(new MyClass<string>(), new object[] { "Hello, World!" }); 
    } 
} 

要使它強類型的你應該簡化，並使用不同的方法：

1）使用表達式獲取動作/方法的name ...

var name = ActionName<object>(x => (o) => x.MyMethod(o)); 

2 ）然後做不可避免的反射部分

var genericType = typeof(MyClass<>).MakeGenericType(new[] { type }); 
MethodInfo genericTypeMyMethodInfo = genericType.GetMethod(name); // "MyMethod"); 

---

其中 ActionName正在採用類似的方法。 OnPropertyChanged(x => x.Property)

public static string ActionName<T>(Expression<Func<MyClass<T>, Action<T>>> expression) 
{ 
    return GetMemberName(expression.Body); 
} 
public static string GetMemberName(Expression expression) 
{ 
    switch (expression.NodeType) 
    { 
     case ExpressionType.Lambda: 
      var lambdaExpression = (LambdaExpression)expression; 
      return GetMemberName(lambdaExpression.Body); 
     case ExpressionType.MemberAccess: 
      var memberExpression = (MemberExpression)expression; 
      var supername = GetMemberName(memberExpression.Expression); 
      if (String.IsNullOrEmpty(supername)) 
       return memberExpression.Member.Name; 
      return String.Concat(supername, '.', memberExpression.Member.Name); 
     case ExpressionType.Call: 
      var callExpression = (MethodCallExpression)expression; 
      return callExpression.Method.Name; 
     case ExpressionType.Convert: 
      var unaryExpression = (UnaryExpression)expression; 
      return GetMemberName(unaryExpression.Operand); 
     case ExpressionType.Parameter: 
      return String.Empty; 
     default: 
      throw new ArgumentException(
       "The expression is not a member access or method call expression"); 
    } 
} 

Answer 2

工作液：

static MethodInfo Resolve (Type type) 
{ 
    Expression<Action<MyClass<object>, object>> lambda = (c, a) => c.MyMethod (a); 
    MethodCallExpression      call = lambda.Body as MethodCallExpression; 
    MethodInfo[]        methods; 
    Type          target; 

    target = call 
     .Method // Get MethodInfo for MyClass<object>.MyMethod 
     .DeclaringType // Get typeof (MyClass<object>) 
     .GetGenericTypeDefinition() // Get typeof (MyClass<>) 
     .MakeGenericType (type); // Get typeof (MyClass<T>) where typeof (T) == type 

    methods = target.GetMethods (BindingFlags.Instance | BindingFlags.NonPublic | BindingFlags.Public | BindingFlags.Static); // We probably don't need static methods 

    return Array.Find (methods, (m) => m.MetadataToken == method.MetadataToken); // Find MyClass<T>.MyMethod where typeof (T) == type 
}