Expression should be MethodCallExpression error calling Expression<Action>

Question

What is the reason for the following code throwing this exception saying "Expression has to be MethodCallExpression. I thought calling an Action IS that..

     Action startBouncePolling = new Action(async () =>
    {

    });

    BackgroundJob.Enqueue(() => startBouncePolling());

Signature of Enqueue is one parameter of Expression<Action>

Answer 1

When you call startBouncePolling(), you're not calling a method. startBouncePolling is not a method, it's a delegate. So you are actually invoking a delegate.

Therefore, the body of the lambda expression () => startBouncePolling() ends up being a InvocationExpression, not a MethodCallExpression.

If you use a method instead of a delegate, for example:

public async Task StartBouncePolling()
{
}
...
BackgroundJob.Enqueue(() => StartBouncePolling());

then the body would be a MethodCallExpression.