一旦我有wifi，如何从xamarin forms android 发送图像？

Question

I'm trying to send images from xamarin forms android to my C# asp.net core MVC web page. 当我有wifi时，我可以做到。 但是当我没有它时，我不能这样做。 当我有wifi回来时，我怎么能发送图像？

基本上，我需要的是存储图像，当用户有 wifi 再次发送图像。

非常感谢！

C# Xamarin forms Android 代码：

string[] subs;
MultipartFormDataContent content2 = new MultipartFormDataContent();
List<StreamContent> listStreamContent = new List<StreamContent>();
List<string> listImgName = new List<string>();
List<string> ControlCantName = new List<string>();
List<int> listDelete = new List<int>();

private async void Scanner()
    {
        try
        {
            var scannerPage = new ZXingScannerPage();
            scannerPage.Title = "scanner";
            scannerPage.OnScanResult += (result) =>
            {
                scannerPage.IsScanning = false;
                string resultado = Convert.ToString(result);
                if (resultado.Contains("http") || resultado.Contains("https"))
                {
                    Browser.OpenAsync(resultado, BrowserLaunchMode.External);
                    Navigation.PopAsync();
                }
                else
                    Device.BeginInvokeOnMainThread(async () =>
                    {
                        Navigation.PopAsync();
                        //Hace el display del valor obtenido
                        subs = result.Text.Split('\t');
                        string cadena = "var1 N°: " + subs[0] + "\var2 N°: " + subs[1] + "\nvar3 N°: " + subs[2];
                        await this.DisplayAlert("Datos del QR", cadena, "OK");
                        takesPhotos();
                    });
            };
            await Navigation.PushAsync(scannerPage);
        }
        catch(Exception ex)
        {
            await DisplayAlert("Error", "We had a problem. Try again", "OK");
            await Shell.Current.GoToAsync($"//{nameof(HomePage)}");
        }
        
    }

private async void takesPhotos()
    {
        try
        {
            var file2 = await MediaPicker.CapturePhotoAsync();

            while (file2 != null)
            {
                Image im = new Image();
                im.ClassId = contador.ToString();
                im.Source = ImageSource.FromFile(file2.FullPath);
                im.HeightRequest = 600;
                im.WidthRequest = 600;
                im.MinimumHeightRequest = 600;
                im.MinimumWidthRequest = 600;
                im.VerticalOptions = LayoutOptions.End;
                im.HorizontalOptions = LayoutOptions.End;
                im.Aspect = Aspect.AspectFill;

                imgs.Children.Add(im);

                Button deleteButton = new Button();
                deleteButton.ClassId = contador.ToString();
                deleteButton.Text = "Delete image";
                deleteButton.VerticalOptions = LayoutOptions.CenterAndExpand;
                deleteButton.HorizontalOptions = LayoutOptions.Center;
                deleteButton.MinimumWidthRequest = 100;
                deleteButton.ClassId = contador.ToString();
                deleteButton.AutomationId = contador.ToString();
                deleteButton.Clicked += async (sender, args) => {
                    listDelete.Add(Convert.ToInt32(deleteButton.ClassId));
                    imgs.Children.Remove(im);
                    imgs.Children.Remove(deleteButton);
                };
                imgs.Children.Add(deleteButton);

                listStreamContent.Add(new StreamContent(await file2.OpenReadAsync()));
                listImgName.Add(subs[0] + "_" + subs[1] + "_" + subs[2] + "_" + contador + "_" + file2.FileName);
                ControlCantName.Add(subs[0] + "_" + subs[1] + "_" + subs[2] + "_" + contador + "_" + file2.FileName);

                file2 = await MediaPicker.CapturePhotoAsync();

                contador++;
            }

            btnScannerQR.IsVisible = false;
            btnSacarFotos.IsVisible = true;
            btnEnviarImagenes.IsVisible = true;
        }
        catch(Exception ex)
        {
            await DisplayAlert("Error", "We had a problem. Try again", "OK");
            await Shell.Current.GoToAsync($"//{nameof(HomePage)}");
        }

private async void sendImages()
    {
        try
        {
            bool answer = await DisplayAlert("¿Have you finished?", "¿are you sure you want to send the images?", "Yes", "No"); 
        
            if(answer)
            {
                int contImgBorradas;
                if (listDelete.Count > 0 || listDelete != null)
                {
                    foreach (var num in listDelete)
                    {
                        contImgBorradas = 1;
                        foreach (var img in ControlCantName)
                        {
                            if (num == contImgBorradas)
                            {
                                listImgName.Remove(num - 1);
                                listStreamContent.Remove(num - 1);
                            }
                            contImgBorradas++;
                        }
                    }
                }

                for (int x = 0; x < listStreamContent.Count; x++)

                {
                    content2.Add(listStreamContent[x], "file", listImgName[x]);
                }

                var httpClient = new HttpClient();
                var response = await httpClient.PostAsync("urlMyWeb", content2);
                string res = await response.Content.ReadAsStringAsync();
                await DisplayAlert("Result", res, "OK");

                btnSacarFotos.IsVisible = false;
                btnEnviarImagenes.IsVisible = false;
                btnScannerQR.IsVisible = true;
                content = null;
                content2 = null;
                imgs.Children.Clear();

                await Shell.Current.GoToAsync($"//{nameof(HomePage)}");
            
            }
        }
        catch(Exception ex)
        {
            await DisplayAlert("Error", "We had a problem. Try again", "OK");
            await Shell.Current.GoToAsync($"//{nameof(HomePage)}");
        }