c# - 如何通过反射判断 C# 方法是否为异步/等待？

Question

例如

class Foo { public async Task Bar() { await Task.Delay(500); } }

如果我们正在反射(reflection)这个类和方法，我如何确定这是否是一个真正的异步/等待方法，而不仅仅是一个碰巧返回任务的方法？

class Foo { public Task Bar() { return Task.Delay(500); } }

Answer 1

在我的代码副本中，async 方法的 MethodInfo 在 CustomAttributes 属性中包含以下项目:

• DebuggerStepThroughAttribute
• 一个AsyncStateMachineAttribute

而普通方法的 MethodInfo 在其 CustomAttributes 属性中包含 no 项。

看起来像 AsyncStateMachineAttribute should reliably be found on an async method and not on a standard one .

编辑:事实上，该页面甚至在示例中包含以下内容!

As the following example shows, you can determine whether a method is marked with Async (Visual Basic) or async (C# Reference) modifier. In the example, IsAsyncMethod performs the following steps:

• Obtains a MethodInfo object for the method name by using Type.GetMethod.

• Obtains a Type object for the attribute by using GetType Operator (Visual Basic) or typeof (C# Reference).

• Obtains an attribute object for the method and attribute type by using MethodInfo.GetCustomAttribute. If GetCustomAttribute returns Nothing (Visual Basic) or null (C#), the method doesn't contain the attribute.

private static bool IsAsyncMethod(Type classType, string methodName)
{
    // Obtain the method with the specified name.
    MethodInfo method = classType.GetMethod(methodName);

    Type attType = typeof(AsyncStateMachineAttribute);

    // Obtain the custom attribute for the method. 
    // The value returned contains the StateMachineType property. 
    // Null is returned if the attribute isn't present for the method. 
    var attrib = (AsyncStateMachineAttribute)method.GetCustomAttribute(attType);

    return (attrib != null);
}