Question

我尝试使用void返回类型编译表达式以使用对象返回类型进行委托。我想在这种情况下获得空值。

var inputArg0 = Expression.Parameter(typeof(object), "arg0");
var inputArg1 = Expression.Parameter(typeof(CancellationToken), "arg1");
var inputArg0Converted = Expression.Convert(inputArg0, inputArg0Type);
var instanceExpression = Expression.Constant(instance);
var call = Expression.Call(instanceExpression, methodInfo, inputArg0Converted, inputArg1);
var lambda = Expression.Lambda<Func<object, CancellationToken, object>>(call, inputArg0, inputArg1);
var _delegate = lambda.Compile();

// works
public string Ping(object e, CancellationToken cancellationToken)
{
    return "OK";
}

// can't compile this MethodInfo to Func<object, CancellationToken, object>
public void Update(ObjectChangedEvent e, CancellationToken cancellationToken)
{
    // do stuff
}

Answer 1

对于void返回类型，您可以使用Action而不是Func来试试这个：

Action<object, CancellationToken, object>

Answer 2

您可以将动作方法包装在返回null的Func中，如下所示：

Func<object, CancellationToken, object> l = (object e, CancellationToken d ) =>
{
    Update((ObjectChangedEvent) e, d);
    return null;
};

如果表达式返回类型为void，如何获取null？

2 个答案: