Xamarin HttpClient 方法 GetAsync 超时错误

Question

我创建了一个 api 来获取数据，但它显示超时错误。我正在调用运行应用程序时调用的 Xamarin 主函数内部的函数。public MainPage()    {        InitializeComponent();        //this.BindingContext = new PatientViewModel();        Task<PatientModel> abc = GetPatientData();    }我的 api GetAsync 调用函数：public async Task<PatientModel> GetPatientData()    {        PatientModel patient = null;        try        {            Uri weburl = new Uri("myuri");            HttpClient client = new HttpClient();            Console.WriteLine("a");            HttpResponseMessage response = await client.GetAsync(weburl);            Console.WriteLine("b");            if (response.IsSuccessStatusCode)            {                Console.WriteLine("in");                patient = await response.Content.ReadAsAsync<PatientModel>();                Console.WriteLine("in funciton");                return patient;            }            return patient;        }catch(Exception ex)        {            Console.WriteLine(ex);            return patient;        }    }}代码没有显示任何错误。当执行到 GetAsync 语句时，它会等待一段时间并发生异常。System.Net.WebException: The request timed out. ---> Foundation.NSErrorException: Exception of type 'Foundation.NSErrorException' was thrown.

Answer 1

考虑使用异步事件处理程序和静态HttpClient

static HttpClient client = new HttpClient();

public MainPage() {

    InitializeComponent();

    loadingData += onLoadingData;        

}

protected override void OnAppearing() {

    //loadingData -= onLoadingData; //(optional)

    loadingData(this, EventArgs.Empty);

    base.OnAppearing();

}

private event EventHandler loadingData = delegate { };

private async void onLoadingData(object sender, EventArgs args) {

    var model = await GetPatientData();

    this.BindingContext = new PatientViewModel(model);

}

public async Task<PatientModel> GetPatientData() {

    PatientModel patient = null;

    try {

        Uri weburl = new Uri("myuri");

        Console.WriteLine("a");

        var response = await client.GetAsync(weburl);

        Console.WriteLine("b");

        if (response.IsSuccessStatusCode) {

            Console.WriteLine("in");

            patient = await response.Content.ReadAsAsync<PatientModel>();

            Console.WriteLine("in funciton");

        }           

    }catch(Exception ex) {

        Console.WriteLine(ex);

    }

    return patient;

}

使用这种模式可以帮助避免阻塞调用和套接字耗尽，这有时会导致死锁，从而导致超时。

Answer 2

尝试这个。

public PatientModel abc { get; set; }

public MainPage()

{

    InitializeComponent();

    Bridge();

    // Using abc

}

public async void Bridge()

{

    abc = new PatientModel();

    abc = await GetPatientData();

}

public async Task<PatientModel> GetPatientData()

{

    PatientModel patient = null;

    try

    {

        Uri weburl = new Uri("myuri");

        HttpClient client = new HttpClient();

        Console.WriteLine("a");

        HttpResponseMessage response = await client.GetAsync(weburl);

        Console.WriteLine("b");

        if (response.IsSuccessStatusCode)

        {

            Console.WriteLine("in");

            patient = await response.Content.ReadAsAsync<PatientModel>();

            Console.WriteLine("in funciton");

            return patient;

        }

        return patient;

    }catch(Exception ex)

    {

        Console.WriteLine(ex);

        return patient;

    }