如何从父类调用异步任务？

Question

Today I need your help to debug my code... Indeed, I need to use the Task object to make API calls but it don't work.

My RestClient to execute my get / post / put requests:

public class RestClient
{
    public HttpClient HttpClient { get; set; }

    public RestClient()
    {
        if(HttpClient == null)
        {
            HttpClient = new HttpClient();
        }
    }

    protected async Task<string> Get(string url)
    {
        // Call url in thread
        HttpResponseMessage response = await HttpClient.GetAsync(url);

        // Get content
        var content = await response.Content.ReadAsStringAsync();

        return content;
    }
}

This problem is here, I cannot to get the return of the base.Get(url). Do you know how I can fix that ?

class CarEnergy : RestClient
{

    public CarEnergy Geter(int id)
    {
        string url = String.Format(Configuration.Configuration.GetCarEnergy, id);

        Debug.WriteLine(url);

        // Wait the get request before continue
        var myTask = base.Get(url); // Impossible to get the return, it bug

        Debug.WriteLine(result);

        var carEnergy = JsonConvert.DeserializeObject<List<CarEnergy>>(result);

        return carEnergy[0];
    }

}

Answer 1

Your Get() method is async , so you have to wait for the result somehow. The best way to do this is to use await . That means your Geter() method also needs to be async , and its caller needs to await , and so on.

Note also that the Get() method is neither virtual or hidden, so you don't need to use base to call it.

Fixing the above results in something that looks like this:

public async Task<CarEnergy> Geter(int id)
{
    string url = String.Format(Configuration.Configuration.GetCarEnergy, id);

    Debug.WriteLine(url);

    // Wait the get request before continue
    var myTask = await Get(url);

    Debug.WriteLine(result);

    var carEnergy = JsonConvert.DeserializeObject<List<CarEnergy>>(result);

    return carEnergy[0];
}

You can block on the async method if you must, by simply retrieving the Result property instead of using await :

    var myTask = Get(url).Result;

(In this case, obviously you don't have to change Geter() to be an async method).

But I strongly discourage doing that. When used correctly, the async / await pattern will wind up woven throughout your code, and will make all of it more UI-friendly and easier to write.