在页面构造函数中异步调用 Web 服务

Question

我需要在 Windows 10 UWP 应用程序的 XAML 页面上加载数据。为此，我编写了代码以在异步任务函数中调用 Web 服务，并在页面构造函数中调用它。你能告诉最好的方法吗？以下是我的代码。

public sealed partial class MyDownloads : Page
{
    string result;
    public  MyDownloads()
    {
        this.InitializeComponent();

        GetDownloads().Wait();
        string jsonstring = result;

        //code for binding follows
    }

    private async Task  GetDownloads()
    {
        JsonObject jsonObject = new JsonObject
        {
            {"StudentID", JsonValue.CreateStringValue(user.Student_Id.ToString()) },
        };

        string ServiceURI = "http://m.xxx.com/xxxx.svc/GetDownloadedNotes";
        HttpClient httpClient = new HttpClient();
        HttpRequestMessage request = new HttpRequestMessage(HttpMethod.Post, ServiceURI);

        request.Content = new StringContent(jsonObject.ToString(), Encoding.UTF8, "application/json");

        HttpResponseMessage response = await httpClient.SendAsync(request);
        string returnString = await response.Content.ReadAsStringAsync();
        result = returnString;
    }
}

Answer 1

您需要使用 OnNavigatedTo

因为，GetDownloads().Wait() 不好的做法。你阻塞 UI 线程直到执行结束

public sealed partial class MainPage : Page
{
    public MainPage()
    {
        this.InitializeComponent();
    }

    protected override async void OnNavigatedTo(NavigationEventArgs e)
    {
        base.OnNavigatedTo(e);

        var result = await GetDownloadsAsync();
        string jsonstring = result;
    }

    private async Task<string> GetDownloadsAsync()
    {
        JsonObject jsonObject = new JsonObject
        {
            {"StudentID", JsonValue.CreateStringValue(user.Student_Id.ToString()) },
        };

        string ServiceURI = "http://m.xxx.com/xxxx.svc/GetDownloadedNotes";
        HttpClient httpClient = new HttpClient();
        HttpRequestMessage request = new HttpRequestMessage(HttpMethod.Post, ServiceURI);

        request.Content = new StringContent(jsonObject.ToString(), Encoding.UTF8, "application/json");

        HttpResponseMessage response = await httpClient.SendAsync(request);
        string returnString = await response.Content.ReadAsStringAsync();
        return returnString;
    }

}