Xamarin.Forms
例外処理

iOSでの例外について報告する1つの方法

iOSプロジェクトの Main.csファイルに移動し、以下に示すようにMain.csコードを変更します。

    static void Main(string[] args)
    {
        try
        {
            UIApplication.Main(args, null, "AppDelegate");
        }
        catch (Exception ex)
        {
            Debug.WriteLine("iOS Main Exception: {0}", ex);

            var watson = new LittleWatson();
            watson.SaveReport(ex);
        }
    }

ポータブルコードで使用されるILittleWatsonインターフェイスは、次のようになります。

public interface ILittleWatson
{
    Task<bool> SendReport();

    void SaveReport(Exception ex);
}

iOSプロジェクトの実装：

[assembly: Xamarin.Forms.Dependency(typeof(LittleWatson))]
namespace SomeNamespace
{
    public class LittleWatson : ILittleWatson
    {
        private const string FileName = "Report.txt";

        private readonly static string DocumentsFolder;
        private readonly static string FilePath;

        private TaskCompletionSource<bool> _sendingTask;

        static LittleWatson()
        {
            DocumentsFolder = Environment.GetFolderPath(Environment.SpecialFolder.MyDocuments);
            FilePath = Path.Combine(DocumentsFolder, FileName);
        }

        public async Task<bool> SendReport()
        {
            _sendingTask = new TaskCompletionSource<bool>();

            try
            {
                var text = File.ReadAllText(FilePath);
                File.Delete(FilePath);
                if (MFMailComposeViewController.CanSendMail)
                {
                    var email = ""; // Put receiver email here.
                    var mailController = new MFMailComposeViewController();
                    mailController.SetToRecipients(new string[] { email });
                    mailController.SetSubject("iPhone error");
                    mailController.SetMessageBody(text, false);
                    mailController.Finished += (object s, MFComposeResultEventArgs args) =>
                    {
                        args.Controller.DismissViewController(true, null);
                        _sendingTask.TrySetResult(true);
                    };

                    ShowViewController(mailController);
                }
            }
            catch (FileNotFoundException)
            {
                // No errors found.
                _sendingTask.TrySetResult(false);
            }

            return await _sendingTask.Task;
        }

        public void SaveReport(Exception ex)
        {
            var exceptionInfo = $"{ex.Message} - {ex.StackTrace}";
            File.WriteAllText(FilePath, exceptionInfo);
        }

        private static void ShowViewController(UIViewController controller)
        {
            var topController = UIApplication.SharedApplication.KeyWindow.RootViewController;
            while (topController.PresentedViewController != null)
            {
                topController = topController.PresentedViewController;
            }

            topController.PresentViewController(controller, true, null);
        }
    }
}

そして、どこかで、どこにアプリが起動するのかを入れます：

        var watson = DependencyService.Get<ILittleWatson>();
        if (watson != null)
        {
            await watson.SendReport();
        }