Xamarin Google 日历示例

Question

我正在尝试让此示例与 Xamarin（Xamarin 表单）一起使用

https://developers.google.com/google-apps/calendar/quickstart/dotnet

我修改了代码，以便 Xamarin Forms 应用程序可以从资源文件加载凭据 json。我通过单步执行代码检查了资源文件是否正在加载。我还修改了 DataStore 类，因为 Xamarin Forms 无法访问示例中指定的路径。

using Google.Apis.Auth.OAuth2;
using Google.Apis.Calendar.v3;
using Google.Apis.Calendar.v3.Data;
using Google.Apis.Services;
using Google.Apis.Util.Store;
using System;
using System.Collections.Generic;
using System.Threading;
using System.Threading.Tasks;
using Xamarin.Forms;
using Xamarin.Forms.Xaml;

namespace TestXamarinFormsLibrary.Pages
{
    [XamlCompilation(XamlCompilationOptions.Compile)]
    public partial class CalendarPage : ContentPage
    {
        public CalendarPage()
        {
            InitializeComponent();
            Go();
        }

        static string[] Scopes = { CalendarService.Scope.CalendarReadonly };
        static string ApplicationName = "Google Calendar API .NET Quickstart";

        private async void Go()
        {
            UserCredential credential;

            var assembly = GetType().Assembly;
            using (var stream = assembly.GetManifestResourceStream("TestXamarinFormsLibrary.client_secret.json"))
            {
                credential = GoogleWebAuthorizationBroker.AuthorizeAsync(
                        GoogleClientSecrets.Load(stream).Secrets,
                        Scopes,
                        "user",
                        CancellationToken.None,
                        new DataStore()).Result;
            }

            // Create Google Calendar API service.
            var service = new CalendarService(new BaseClientService.Initializer()
            {
                HttpClientInitializer = credential,
                ApplicationName = ApplicationName,
            });

            // Define parameters of request.
            EventsResource.ListRequest request = service.Events.List("primary");
            request.TimeMin = DateTime.Now;
            request.ShowDeleted = false;
            request.SingleEvents = true;
            request.MaxResults = 10;
            request.OrderBy = EventsResource.ListRequest.OrderByEnum.StartTime;

            // List events.
            Events events = request.Execute();
            if (events.Items != null && events.Items.Count > 0)
            {
                foreach (var eventItem in events.Items)
                {
                    string when = eventItem.Start.DateTime.ToString();
                    if (String.IsNullOrEmpty(when))
                    {
                        when = eventItem.Start.Date;
                    }
                    await DisplayAlert("ok", $"{eventItem.Summary} ({when})", "ok");
                }
            }
        }
    }

    public class DataStore : IDataStore
    {
        private Dictionary<string, object> Data = new Dictionary<string, object>();

        public Task ClearAsync()
        {
            throw new NotImplementedException();
        }

        public Task DeleteAsync<T>(string key)
        {
            throw new NotImplementedException();
        }

        public async Task<T> GetAsync<T>(string key)
        {
            if (Data.ContainsKey(key))
            {
                return (T)Data[key];
            }

            return default(T);
        }

        public async Task StoreAsync<T>(string key, T value)
        {
            Data.Add(key, value);
        }
    }
}

这是我运行时遇到的错误：

也不例外。我在 Android 上遇到类似的错误。我的猜测是它依赖 oAuth 库来打开 Web 浏览器，以尝试允许身份验证，但 Xamarin Forms 没有实现此行为。我也尝试过打开所有 UWP 功能，但这没有帮助。

如何让 Xamarin Forms 运行示例？

Answer 1

.NET 客户端的 repo 在这里： https://github.com/google/google-api-dotnet-client

我想我可以从源代码中弄清楚这一点，但我还没有尝试过。

Answer 2

我的 UWP 应用中有 Google .NET 客户端。诀窍是您必须将其放入 .NET Standard 2.0 类库中，公开您需要的 API 服务，然后从您的 UWP 应用程序中引用该库。

此外，您必须自己处理获取身份验证令牌。这不是很多工作，Drive API 和 Calendar API 工作得很好（我唯一尝试过的）。您可以看到，我将一个包含身份验证令牌和其他身份验证详细信息的简单类传递给了一个名为 Initialize 的方法。

这是我在 .NET Standard 2.0 类库中使用的单个类：

namespace GoogleProxy
{
public class GoogleService
{
    public CalendarService calendarService { get; private set; }

    public DriveService driveService { get; private set; }


    public GoogleService()
    {

    }

    public void Initialize(AuthResult authResult)
    {
        var credential = GetCredentialForApi(authResult);
        var baseInitializer = new BaseClientService.Initializer { HttpClientInitializer = credential, ApplicationName = "{your app name here}" };

        calendarService = new Google.Apis.Calendar.v3.CalendarService(baseInitializer);
        driveService = new Google.Apis.Drive.v3.DriveService(baseInitializer);
    }

    private UserCredential GetCredentialForApi(AuthResult authResult)
    {
        var initializer = new GoogleAuthorizationCodeFlow.Initializer
        {
            ClientSecrets = new ClientSecrets
            {
                ClientId = "{your app client id here}",
                ClientSecret = "",
            },
            Scopes = new string[] { "openid", "email", "profile",  "https://www.googleapis.com/auth/calendar.readonly", "https://www.googleapis.com/auth/calendar.events.readonly", "https://www.googleapis.com/auth/drive.readonly" },
        };

        var flow = new GoogleAuthorizationCodeFlow(initializer);

        var token = new TokenResponse()
        {
            AccessToken = authResult.AccessToken,
            RefreshToken = authResult.RefreshToken,
            ExpiresInSeconds = authResult.ExpirationInSeconds,
            IdToken = authResult.IdToken,
            IssuedUtc = authResult.IssueDateTime,
            Scope = "openid email profile https://www.googleapis.com/auth/calendar.readonly https://www.googleapis.com/auth/calendar.events.readonly https://www.googleapis.com/auth/drive.readonly",
            TokenType = "bearer" };

        return new UserCredential(flow, authResult.Id, token);
    }

}
}

UWP 的完整答案在这里： https://stackoverflow.com/a/53971436/1938624