等待运算符出错

Question

我的代码有问题.我怎么解决这个问题？等待运算符中存在此问题.

 public MyModel() 
    {
        HttpClient client = new HttpClient();
        HttpResponseMessage response = await client.GetAsync("https://api.vkontakte.ru/method/video.get?uid=219171498&access_token=d61b93dfded2a37dfcfa63779efdb149653292636cac442e53dae9ba6a049a75637143e318cc79e826149");
        string googleSearchText = await response.Content.ReadAsStringAsync();
        JObject googleSearch = JObject.Parse(googleSearchText);
        IList<JToken> results = googleSearch["response"].Children().Skip(1).ToList();
        IList<MainPage1> searchResults = new List<MainPage1>();
        foreach (JToken result in results)
        {
            MainPage1 searchResult = JsonConvert.DeserializeObject<MainPage1>(result.ToString());
            searchResults.Add(searchResult);

        }

Answer 1

您正尝试await在构造函数中使用.你做不到 - 构造函数总是同步的.

您只能await在方法或匿名函数中使用async修饰符; 你不能将该修饰符应用于构造函数.

解决这个问题的一种方法是创建一个静态异步方法来创建一个实例 - 它将执行所有相关的等待,然后将结果传递给一个简单的同步构造函数.当然,你的呼叫者需要适当地处理这个问题.

public static async Task<MyModel> CreateInstance()
{
    string googleSearchText;
    using (HttpClient client = new HttpClient())
    {
        using (HttpResponseMessage response = await client.GetAsync(...))
        {
            googleSearchText = await response.Content.ReadAsStringAsync();
        }
    }
    // Synchronous constructor to do the rest...
    return new MyModel(googleSearchText);
}

Answer 2

您不能在类的构造函数中使用await.

异步方法返回一个Task可以执行异步的对象.构造函数没有返回类型,因此无法返回Task对象,因此无法等待.

解决此问题的一个简单方法是创建一个Init函数:

public MyModel() 
{

}

public async Task Init()
{
    HttpClient client = new HttpClient();
    HttpResponseMessage response = await client.GetAsync("https://api.vkontakte.ru/method/video.get?uid=219171498&access_token=d61b93dfded2a37dfcfa63779efdb149653292636cac442e53dae9ba6a049a75637143e318cc79e826149");
    string googleSearchText = await response.Content.ReadAsStringAsync();
    JObject googleSearch = JObject.Parse(googleSearchText);
    IList<JToken> results = googleSearch["response"].Children().Skip(1).ToList();
    IList<MainPage1> searchResults = new List<MainPage1>();
    foreach (JToken result in results)
    {
        MainPage1 searchResult = JsonConvert.DeserializeObject<MainPage1>(result.ToString());
        searchResults.Add(searchResult);

    }
}

然后在创建模型时:

var model = new MyModel();
await model.Init();