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How to go to main page after buttom back with ZXingScannerPage in C# xamarin forms android?

I'm working with C# xamarin forms android and I'm trying to go back using OnBackButtonPressed. It kind of works but my problem is that the user has to touch 2 times to go back. I will left a photo below to explain my point. But basically the user goes from Home page to Scaner page and when he touch buttom back when he is scanning doesn't come back to home page. He has to touch 2 times and i don't want that. I need that when he touches the buttom back he goes to the home page.
my scanPage.xaml.cs:
protected override bool OnBackButtonPressed()
{
try
{
if (Shell.Current.FlyoutIsPresented == false)
{
Shell.Current.GoToAsync($"//{nameof(HomePage)}");
}
else
{
Shell.Current.FlyoutIsPresented = false;
}
}
catch(Exception ex)
{
}
//return base.OnBackButtonPressed();
return true;
}
private async Task Scanner()
{
try
{
var scannerPage = new ZXingScannerPage();
scannerPage.AutoFocus();
scannerPage.Title = "Scanner";
using (SemaphoreSlim semaphoreSlim = new SemaphoreSlim(0, 1))
{
scannerPage.OnScanResult += (result) =>
{
scannerPage.IsScanning = false;
string resultado = Convert.ToString(result);
if (resultado.Contains("http") || resultado.Contains("https") || !resultado.Contains("\t"))
{
Navigation.PopAsync();
this.DisplayAlert("Error", "QR not valid", "OK");
}
else
Device.BeginInvokeOnMainThread(async () =>
{
try
{
await Application.Current.MainPage.Navigation.PopAsync();
subs = result.Text.Split('\t');
string cadena = "var 1: " + subs[0] + "\nvar 2: " + subs[1] + "\nvar 3: " + subs[2];
numEntrega.Text = "var 2: " + subs[1];
controlScanner = true;
await this.DisplayAlert("Data", cadena, "OK");
}
catch (Exception ex)
{
checkDoubleCalled = true;
controlScanner = false;
numEntrega.Text = "";
await DisplayAlert("Error", "QR not valid.\n try again.", "OK");
await Shell.Current.GoToAsync($"//{nameof(HomePage)}");
}
semaphoreSlim.Release();
});
};
await Navigation.PushAsync(scannerPage);
await semaphoreSlim.WaitAsync();
}
return;
}
catch(Exception ex)
{
checkDoubleCalled = true;
controlScanner = false;
numEntrega.Text = "";
await DisplayAlert("Error", "Sorry we had a problem.", "OK");
await Shell.Current.GoToAsync($"//{nameof(HomePage)}");
}
return;
}
Image of my problem:
How could I resolve this problem?
Thank you very much!

display multiple permission at once xamarin forms

I am creating a Xamarin Form PCL project for Android and IOS.
Is this possible to display multiple permission at once on the screen? My App is using Location, Storage and Camera permission. From my current code, this is displaying permission popup one by one on the different page like before use of camera i display camera permission popup. As I know three permission required for my App so i want to display a single popup for all three permission.
Below is my code for storage permission.
public static async Task<dynamic> CheckStoragePermission()
{
var result = "";
try
{
var Storagestatus = await CrossPermissions.Current.CheckPermissionStatusAsync(Plugin.Permissions.Abstractions.Permission.Storage);
if (Storagestatus != PermissionStatus.Granted)
{
await Utils.CheckPermissions(Plugin.Permissions.Abstractions.Permission.Storage);
}
}
catch (Exception ex)
{
error(ex.Message, Convert.ToString(ex.InnerException), ex.Source, ex.StackTrace);
}
return result;
}
Hope someone did this before in xamarin forms, I will thank for your help for this.

You could try using the following code to request multiple permissions at one time:
private async void Button_Clicked(object sender, EventArgs e)
{
await GetPermissions();
}
public static async Task<bool> GetPermissions()
{
bool permissionsGranted = true;
var permissionsStartList = new List<Permission>()
{
Permission.Location,
Permission.LocationAlways,
Permission.LocationWhenInUse,
Permission.Storage,
Permission.Camera
};
var permissionsNeededList = new List<Permission>();
try
{
foreach (var permission in permissionsStartList)
{
var status = await CrossPermissions.Current.CheckPermissionStatusAsync(permission);
if (status != PermissionStatus.Granted)
{
permissionsNeededList.Add(permission);
}
}
}
catch (Exception ex)
{
}
var results = await CrossPermissions.Current.RequestPermissionsAsync(permissionsNeededList.ToArray());
try
{
foreach (var permission in permissionsNeededList)
{
var status = PermissionStatus.Unknown;
//Best practice to always check that the key exists
if (results.ContainsKey(permission))
status = results[permission];
if (status == PermissionStatus.Granted || status == PermissionStatus.Unknown)
{
permissionsGranted = true;
}
else
{
permissionsGranted = false;
break;
}
}
}
catch (Exception ex)
{
}
return permissionsGranted;
}

Android error: Nested signal detected - original signal being reported

This is killing me. I'm new to android/Xamarin. I can't find anything on the web that explains what is going on here.
I'm using xamarin forms for my application. I have a page that synchronizes the device with a web service.
The method simply retrieves 100 records at a time from the web service and updates a sqlite table on the device. I randomly get this error. I'm running 5000 records for my test sample.
Here is the button click:
public async void OnSyncCachedData_Clicked(object sender, EventArgs e)
{
activityIndicatorAll.IsRunning = true;
try
{
actIndSyncItems.IsRunning = true;
SyncAllFinished += SynchAllFinishedProcessing;
await Task.Run(async () => await App.ItemsRepo.LoadCacheDataFromCacheAsync(DbPath).ConfigureAwait(false));
}
catch (BAL.Exceptions.NetworkException nex)
{
await DisplayAlert(Messages.TitleError, nex.Message, Messages.MsgOk);
}
catch (Exception ex)
{
await DisplayAlert(Messages.TitleError, string.Format(Messages.MsgAreYouConnectedParm1, ex.Message), Messages.MsgOk);
}
finally
{
EventHandler handler = SyncAllFinished;
if (handler != null)
{
handler(this, new EventArgs());
}
SyncAllFinished -= SynchAllFinishedProcessing;
}
}
the main worker method:
public async Task<bool> LoadCacheDataFromCacheAsync(string dbPath)
{
WebSvcManagers.ItemsManager itemsWebServiceManager = new WebSvcManagers.ItemsManager();
List<Models.WebServiceItems> consumedRecords = new List<Models.WebServiceItems>() { };
int bufferSize = 100;
Log.Debug(TAG, "LoadCacheDataFromCacheAsync starting");
try
{
{
int lastID = 0;
IEnumerable<Models.WebServiceItems> remoteRecords = await BAL.DataAccessHelper.GetItemsFromGPCacheAsync(App.Login, lastID, bufferSize, itemsWebServiceManager).ConfigureAwait(false);
while (remoteRecords.Count() != 0)
{
foreach (Models.WebServiceItems remoteItem in remoteRecords)
{
// DbActionTypes dbAction = (DbActionTypes)remoteItem.DbAction;
Models.Items itemRecord = new Models.Items() { ItemNumber = remoteItem.ItemNumber.ToUpper().Trim(), Description = remoteItem.Description.Trim() };
Log.Debug(TAG, "Processing {0}", remoteItem.ItemNumber.Trim());
bool success = await AddRecordAsync(itemRecord).ConfigureAwait(false);
if (success)
consumedRecords.Add(remoteItem);
}
lastID = remoteRecords.Max(r => r.RecordID) + 1;
remoteRecords = await BAL.DataAccessHelper.GetItemsFromGPCacheAsync(App.Login, lastID, bufferSize, itemsWebServiceManager).ConfigureAwait(false);
}
}
// await UpdateConsumedRecords(consumedRecords).ConfigureAwait(false);
return true;
}
catch (Exception ex)
{
this.StatusMessage = ex.Message;
Log.Debug(TAG, "Error Catch: {0}", StatusMessage);
return false;
}
finally
{
itemsWebServiceManager = null;
HandleSyncFinished(this, new EventArgs());
SyncAllFinished -= HandleSyncFinished;
}
}
My simple webservice manager:
public static async Task<IEnumerable<Models.WebServiceItems>> GetItemsFromGPCacheAsync(Models.Login login, int offset, int bufferCount, WebSvcManagers.ItemsManager manager)
{
try
{
return await manager.GetCacheRecordsAsync(login, offset, bufferCount).ConfigureAwait(false);
}
catch (Exception)
{
throw;
}
}
And the code for the interaction with the web service:
const int bufferSize = 100;
public async Task<IEnumerable<Models.WebServiceItems>> GetCacheRecordsAsync(Models.Login login, int offSet, int bufferCount)
{
string deviceID = App.ConfigSettings.DeviceID.ToString("D");
try
{
///* Testing start */
//return await DataStore(bufferCount, offSet).ConfigureAwait(false);
///* Testing end */
if (!App.IsConnected)
throw new BAL.Exceptions.NetworkException(Messages.ExceptionNetworkConnection);
string user = login.UserName;
string password = login.Password;
HttpClient client = HttpClientExtensions.CreateHttpClient(user, password);
try
{
List<Models.WebServiceItems> items = new List<Models.WebServiceItems>() { };
int lastID = offSet;
int i = 0;
string uri = string.Format("{0}", string.Format(Messages.WebRequestItemsCacheParms3, deviceID, lastID, Math.Min(bufferCount, bufferSize)));
Log.Debug(TAG, string.Format("Webservice {0}", uri));
string response = await client.GetStringAsync(uri).ConfigureAwait(false);
while (i < bufferCount && response != null && response != "[]")
{
while (response != null && response != "[]")
{
dynamic array = JsonConvert.DeserializeObject(response);
foreach (var item in array)
{
i++;
items.Add(new Models.WebServiceItems()
{
ItemNumber = item["ITEMNMBR"].Value.Trim(),
Description = item["ITEMDESC"].Value.Trim(),
DbAction = (int)(item["DbAction"].Value),
RecordID = (int)(item["DEX_ROW_ID"].Value),
});
lastID = (int)(item["DEX_ROW_ID"].Value);
Log.Debug(TAG, string.Format("Webservice {0}", item["ITEMNMBR"].Value.Trim()));
}
if (i < Math.Min(bufferCount, bufferSize))
{
uri = string.Format("{0}", string.Format(Messages.WebRequestItemsCacheParms3, deviceID, lastID + 1, Math.Min(bufferCount, bufferSize)));
Log.Debug(TAG, string.Format("Webservice {0}", uri));
response = await client.GetStringAsync(uri).ConfigureAwait(false);
}
else
break;
}
}
Log.Debug(TAG, string.Format("Webservice return {0} items", items.Count()));
return items;
}
catch (Exception ex)
{
Log.Debug(TAG, "Error Catch: {0}", ex.Message);
throw ex;
}
}
catch (System.Net.Http.HttpRequestException nex)
{
throw new Exception(string.Format(Messages.ExceptionWebServiceLoginParm1, nex.Message));
}
catch (Exception)
{
throw;
}
}
I've had assistance from a Xamarin instructor and we thought we got it, (because this is random), but it clearly is not swatted. I've been hitting my head up against a wall for over 3 weeks on this. It smells like a memory leak, but I have no idea how to find it with such a generic error message that doesn't appear on web searches.
Somebody out there with some major brains, Please help!
Error:
08-03 12:41:11.281 D/X:ItemsRepositiory(16980): UpdateRecordAsync 65702-40710
08-03 12:41:11.306 D/X:ItemsManager(16980): Webservice DeleteCacheRecordAsync 20497
08-03 12:41:11.406 D/X:ItemsManager(16980): Webservice api/InventoryItems?DeviceID=7c5bb45d-2ea0-45b9-ae50-92f2e25a2983&OffSet=20498&Ma‌​x=100&cached=true
Thread finished: <Thread Pool> #7 08-03 12:41:11.521 E/art (16980): Nested signal detected - original signal being reported The thread 'Unknown' (0x7) has exited with code 0 (0x0).

This might be a problem with the VS Android Emulator. As we have shown in tests, this is not reproducible on the Google Android Emulators, nor on Xamarin Android Player, nor on a physical Android device.

C# Recursive function approach?

I have a recursive function in a windows service. This function upon completion rewinds itself as it has been repeated multiple times in recursion. Isn't that an overhead ?
Is there any way to avoid unwinding ? Is there any better approach?
Edit : In this method, I get 100 records from DB and then process them and then get another 100 and so on till all the records in DB have been processed.
Also, there is no limit of how many total records there might be in the db so this function can repeat itself quite a lot.
public void ServiceFunctionality()
{
try
{
// Get Data From WEBAPI
HttpClient client = new HttpClient();
HttpResponseMessage response = response = client.GetAsync("webapi url link").Result;
Response<ServiceWrapper> objResponse = response.Content.ReadAsAsync<Response<ServiceWrapper>>().Result;
if (objResponse != null)
{
if (objResponse.isSuccess == true)
{
listContact = objResponse.data.lContact;
int MaxPKinSelectedRecords = objResponse.data.MaxPKinSelectedRecords;
int MaxPKinTotalRecords = objResponse.data.MaxPKinTotalRecords;
if (listContact != null && listContact.Count>0)
{
try
{
Parallel.ForEach(listContact, contact =>
{
// some code...
});
// Recursive Call
if (MaxPKinTotalRecords != MaxPKinSelectedRecords)
{
ServiceFunctionality();
}
}
catch (Exception ex)
{
// Logging
}
}
}
else
{
// Logging
}
}
else
{
// Logging
}
}
catch (Exception ex)
{
// Logging
}
}

You can always unwind to a while loop. Because your calls aren't altering state, this is trival.
public void ServiceFunctionality()
{
bool done = false;
while(!done) {
try
{
done = true; //if we don't reset this, we're done.
// Get Data From WEBAPI
HttpClient client = new HttpClient();
HttpResponseMessage response = response = client.GetAsync("webapi url link").Result;
Response<ServiceWrapper> objResponse = response.Content.ReadAsAsync<Response<ServiceWrapper>>().Result;
if (objResponse != null)
{
if (objResponse.isSuccess == true)
{
listContact = objResponse.data.lContact;
int MaxPKinSelectedRecords = objResponse.data.MaxPKinSelectedRecords;
int MaxPKinTotalRecords = objResponse.data.MaxPKinTotalRecords;
if (listContact != null && listContact.Count>0)
{
try
{
Parallel.ForEach(listContact, contact =>
{
// some code...
});
// set loop variable
if (MaxPKinTotalRecords != MaxPKinSelectedRecords)
{
done = false;
}
}
catch (Exception ex)
{
// Logging
}
}
}
else
{
// Logging
}
}
else
{
// Logging
}
}
catch (Exception ex)
{
// Logging
}
}
}

Do not use recursion for calling a function whenever you have alternate suitable solution. I personally almost never do
I have tried to keep it same other than using a while..
Do not forget to break your loop. I tried to handle this thing but still
Just to be very careful, never take a risk of infinite loop on server I took maxPossibleIterations. So that in case of any mistake your web service server would not have to go for infinite iterations
public void ServiceFunctionality()
{
long maxPossibleIterations = 999999;
try
{
while (true)
{
maxPossibleIterations++;
// Get Data From WEBAPI
HttpClient client = new HttpClient();
HttpResponseMessage response = response = client.GetAsync("webapi url link").Result;
Response<ServiceWrapper> objResponse = response.Content.ReadAsAsync<Response<ServiceWrapper>>().Result;
if (objResponse != null)
{
if (objResponse.isSuccess == true)
{
listContact = objResponse.data.lContact;
int MaxPKinSelectedRecords = objResponse.data.MaxPKinSelectedRecords;
int MaxPKinTotalRecords = objResponse.data.MaxPKinTotalRecords;
if (listContact != null && listContact.Count>0)
{
try
{
Parallel.ForEach(listContact, contact =>
{
// some code...
});
if (MaxPKinTotalRecords == MaxPKinSelectedRecords)
{
break;
}
}
catch (Exception ex)
{
// Logging
}
}
else
break; //Important
}
else
{
// Logging
break;
}
}
else
{
// Logging
break;
}
} // End while
}
catch (Exception ex)
{
// Logging
}
}

Permission screen appears every time

I want to make my WinForms-App to use the SingleSign-On (SSO) feature with Microsoft Accounts.
I created a LiveApp and I'm able to Login to my App with the LiveSDK 5.4.
But everytime I click on my Login-Button the permissions list appears and I need to accept it again.
This is my code:
private const string ClientID = "{MY_CLIENT_ID}";
private LiveAuthClient liveAuthClient;
private LiveConnectClient liveConnectClient;
string[] scopes = new string[] { "wl.offline_access", "wl.emails", "wl.signin" };
private void buttonLogin_Click(object sender, EventArgs e)
{
liveAuthClient = new LiveAuthClient(ClientID);
webBrowser1.Navigate(liveAuthClient.GetLoginUrl(scopes));
}
private async void webBrowser1_Navigated(object sender, WebBrowserNavigatedEventArgs e)
{
if (this.webBrowser1.Url.AbsoluteUri.StartsWith("https://login.live.com/oauth20_desktop.srf"))
{
AuthResult authResult = new AuthResult(this.webBrowser1.Url);
if (authResult.AuthorizeCode != null)
{
try
{
LiveConnectSession session = await liveAuthClient.ExchangeAuthCodeAsync(authResult.AuthorizeCode);
this.liveConnectClient = new LiveConnectClient(session);
LiveOperationResult meRs = await this.liveConnectClient.GetAsync("me");
dynamic meData = meRs.Result;
if(string.Equals(meData.emails.account, MyAppUser.EmailAddress))
MessageBox.Show("Successful login: " + meData.name);
}
catch (LiveAuthException aex)
{
MessageBox.Show("Failed to retrieve access token. Error: " + aex.Message);
}
catch (LiveConnectException cex)
{
MessageBox.Show("Failed to retrieve the user's data. Error: " + cex.Message);
}
}
else
{
MessageBox.Show(string.Format("Error received. Error: {0} Detail: {1}", authResult.ErrorCode, authResult.ErrorDescription));
}
}
}
What I need to change? I don't want the User to accept the permissions on each login.

You can use IRefreshTokenHandler to save token as following example:
public class RefreshTokenHandler : IRefreshTokenHandler
{
private string path = Environment.GetFolderPath(Environment.SpecialFolder.ApplicationData) + "\\oneDrive\\RefreshTokenHandler\\RefreshTokenInfo.RefreshToken-me";
public Task<RefreshTokenInfo> RetrieveRefreshTokenAsync()
{
return Task.Factory.StartNew<RefreshTokenInfo>(() =>
{
if (File.Exists(path))
{
return new RefreshTokenInfo(File.ReadAllText(path));
}
return null;
});
}
public Task SaveRefreshTokenAsync(RefreshTokenInfo tokenInfo)
{
// Note:
// 1) In order to receive refresh token, wl.offline_access scope is needed.
// 2) Alternatively, we can persist the refresh token.
return Task.Factory.StartNew(() =>
{
if (File.Exists(path)) File.Delete(path);
if (!Directory.Exists(Path.GetDirectoryName(path))) Directory.CreateDirectory(Path.GetDirectoryName(path));
File.AppendAllText(path, tokenInfo.RefreshToken);
});
}
}
after that you get session as following:
RefreshTokenHandler handler = new RefreshTokenHandler();
liveAuthClient = new LiveAuthClient(ClientID, handler);
var Session = liveAuthClient.InitializeAsync(scopes).Result.Session;
if (Session == null)
{
webBrowser1.Navigate(liveAuthClient.GetLoginUrl(scopes));
}
else
{
try
{
this.liveConnectClient = new LiveConnectClient(Session);
LiveOperationResult meRs = await this.liveConnectClient.GetAsync("me");
dynamic meData = meRs.Result;
if (string.Equals(meData.emails.account, MyAppUser.EmailAddress))
MessageBox.Show("Successful login: " + meData.name);
}
catch (LiveAuthException aex)
{
MessageBox.Show("Failed to retrieve access token. Error: " + aex.Message);
}
catch (LiveConnectException cex)
{
MessageBox.Show("Failed to retrieve the user's data. Error: " + cex.Message);
}
}

I've only used this API in Objective C, but I had to follow two steps.
Use the wl.offline_access scope. (Which you're already doing)
You only show the login screen if the sessions object is null. If your session object is already populated, you can proceed as you would if the sign in was successful.