将覆盖的成员更改为异步 [英] Change overridden member to async

问题描述

我正在重写基类库中的方法.但是，在我的重写实现中，我正在使用新的HttpClient，它全部基于异步方法.因此，我必须将我的方法标记为异步，这意味着我需要将方法的返回参数从字符串更改为Task.但是，编译器给出了一个错误:返回类型必须为'string'才能匹配被重写的成员...."

I am overriding a method in a base class library. However, inside my overridden implementation I am using the new HttpClient which is all based on async methods. I therefore have to mark my method as async, which means that I need to change the return parameter of the method from string to Task. The compiler however gives an error: "The return type must be 'string' to match overridden member ...."

    public class BaseClass
    {
        public virtual string GetName()
        {
            ...
        }
    }

    public class MyClass : BaseClass
    {
        public override async Task<string> GetName()
        {
            HttpClient httpClient = new HttpClient();
            var response = await httpClient.GetAsync("");
            if (response.IsSuccessStatusCode)
            {
                var responseContent = response.Content;

                return await responseContent.ReadAsStringAsync();
            }

            return null;
        }
    }

当然，显而易见的解决方案是将BaseClass中的GetName()的返回类型更改为Task< string> ;，但是我无法控制BaseClass，因为它是一个外部库；

Of course the obvious solution would be to change the return type of GetName() in BaseClass to Task<string>, but I have no control over BaseClass as it is an external library;

我当前的解决方案是以同步方式使用HttpClient类，即如下更改MyClass:

My current solution is to use the HttpClient classes in a synchronous fashion, i.e. change MyClass as follows:

    public class MyClass : BaseClass
    {
        public override string GetName()
        {
            HttpClient httpClient = new HttpClient();
            var response = httpClient.GetAsync("");
            if (response.Result.IsSuccessStatusCode)
            {
                var responseContent = response.Result.Content;

                return responseContent.ReadAsStringAsync()
                                                       .Result;
            }

            return null;
        }
    }

还有其他方法吗?

推荐答案

不幸的是，这里没有一个好的解决方案.没有办法用异步方法覆盖非异步方法.我认为您最好的选择是拥有一个 async 非重写方法，并从非异步方法调用该方法:

Unfortunately there isn't a good solution here. There is no way to override a non-async method with an async one. I think your best bet is to have an async non-override method and call into that from the non-async one:

public class MyClass : BaseClass 
{
    public override string GetName() 
    {
        return GetNameAsync().Value;
    }

    public async Task<string> GetNameAsync() 
    { 
        ...
    }
}

请注意，这可能会导致问题.如果原始代码不希望执行任何 async 代码，则引入此模式可能会超出预期.如果可能的话，我会避免.

Note that this can cause problems though. If the original code didn't expect for any async code to be executing introducing this pattern could break expectations. I would avoid it if possible.

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