从消费类获取警告

Question

Let's say I have a service class that does something for me and a consumer class that consumes this service. The service relies on throwing exceptions to the consumer when it feeds it something that won't work.

All is good, I can easily catch these exceptions from the consuming side and do something useful with them. Like displaying a message to the user.

However, what if the service run into something that's not good, but not really an error. It may be some information to the user saying "Don't do it this way, it'll work but you've probably made a mistake". A warning that is.

How would you go about notifying the consumer class of this warning so it can be for example shown to the user? Is the only way to pass some sort of warning service (much like a logger) to the service and then check that for any warnings after the service is done?

I should also say that the service is within my domain so I can do pretty much what I want with it.

Answer 1

Have you thought about your consumer class throwing events and have your service class subscribe to them? See here

Answer 2

I would think about wrapping the entire service call into a context, something like this:

class CallContext<TInput, TOutput>
{
    TInput InputValue { get; set; }

    TOutput OutputValue { get; set; }

    ICollection<String> Warnings { get; set; }
}

class MyService
{
    void SomeOperation(CallContext<int, int> context)
    {
        context.OutputValue = context.InputValue * 2;

        if (context.IntputValue < 0)
            context.Warnings.Add("Input value less than zero may have undesired results.");
    }
}

The service is quite happy to continue with the operation despite the fact that it has recognised something peculiar with the input. It doesn't stop the function running, but the service is able to warn the caller that the result may be unexpected.

class Consumer
{
    void CallService()
    {
        var context = new Context<int, int>()
        {
            InputValue = -1;
        }

        myService.SomeOperation(context);

        Console.WriteLine(context.OutputValue);

        foreach(string warning in context.Warnings)
            Console.Writeline(warning);
    }
}