How can I create a login page in Xamarin.Forms? - xamarin

Question

How can I create a login page using Xamarin.Forms?
I'm debugging on Android device and
on the page I try to query the given username and password from an MSSQL database in MSSQL
and if the login be successful, the page will navigate to a new page, else will show authentication failed.
How can I do this in Xamarin.Forms?

Answer 1

(Xamarin LoginFlow Example linked at bottom of answer)
You would have multiple Xamarin.Forms pages and use a NavigationPage to push or pop them from the (lifecycle) stack.
Ref: https://developer.xamarin.com/api/type/Xamarin.Forms.NavigationPage/
Think of each Page a complete self-contained mini application. So the Login page might handle the getting the UserID/Password interactively from the user, performing a authorization check via a server via a Rest api that performs your SQL query. If login is successful it pushes a new Forms-based page on the NavigationPage stack. i.e.
SplashScreen -> LoginPage -> MainPagePage
LoginFlow Xamarin example
This sample demonstrates how to manipulate the navigation stack in order to only display the main page of the application once the user has successfully logged in.
For more information about the sample see Hierarchical Navigation.

Answer 2

What you need is the following functionalities:
Web APIs (Web Service for Login - Hosted on internet or local network - Connected with your MSSql Server)
A Login Screen in Xamarin.Forms Application (You can design it on your own or use the above mentioned demo)
On Login Screen's 'Login' button click, you need to call the Login Web Service from Xamarin.Forms application.
This requires networking (Internet Permission on Android Project, through Manifest.xml). You can use Microsoft.Net.Http for Web Service Calls.
(Look at this example http://www.c-sharpcorner.com/UploadFile/nirmal.hota/consuming-restful-web-service-in-xamarin-forms-project-using/ )
If your server responses with JSON and you need to parse JSON then you can use Json.Net (Newtonsoft.Json).
Note: What I am trying to tell you is that you need to use Web Services that are connected to the database and hosted on a server. From Xamarin.Forms application, you have to call this web-service with appropriate parameters. This requires networking, so you can use Microsoft.Net.Http (or there are other plugins also available). To get response from the Web Service, if it is in Json then you can use Newtonsoft.Json to parse Json.

Answer 3

There is a full example of an app with login page: xamarin-forms-samples/LoginDemo/ provided by Xamarin.

Answer 4

So lets say you have a LoginController on asp.net web api (if you don't know how to create an asp.net web api project etc. this is not the place to learn it:) )
[RoutePrefix("v1/login")]
public class LoginController : ApiController
{
[Route("")]
[HttpPost] //I'm using post!!!!!! you may use get etc.
public IHttpActionResult Login(UserLoginData request)
{
var userData = CheckFromDb(request);
return Json(userData);
}
}
It checks your request from db (UserLoginData is a simple class lets say holds username and password), than if user exists you return another class (lets say it is UserData hat holds name,surname, birthday etc.). If it can not find login it may return null. It's up to you.
So it will be available on your host machine like
localhost:34252/v1/login
(34252 your port-may change for you)
So you have to call it from the device (xamarin.forms) code like this
public string Post(string url, UserLoginData userLoginData)
{
//url is login url as defined above and userLoginData holds your
//user interface (textbox) data :)
using (var client = new HttpClient())
{
client.Timeout = new TimeSpan(0, 0, 30);
client.DefaultRequestHeaders.Accept.Clear();
client.DefaultRequestHeaders.Accept.Add(new MediaTypeWithQualityHeaderValue("application/json"));
StringContent content;
content = new StringContent(JsonConvert.SerializeObject(userLoginData), Encoding.UTF8, "application/json");
HttpResponseMessage response = client.PostAsync(url, content).Result;
if (!response.IsSuccessStatusCode)
{
throw new Exception("call failed");
}
//this is your response as json
var responseString = response.Content.ReadAsStringAsync().Result;
//you can convert it and check to a specific class if you need
var userData = JsonConvert.DeserializeObject<UserData>(responseString);
}
}
So UserLoginData and UserData classes both must exists on both sides. You can use Newtonsoft.Json library for json parsing (jsonconvert is it's method). Hope this helps you
And android device simulator networking is a bit tricky. You may not connect to localhost directy. It may take an address like 10.0.2.* for androidemulator or 10.71.34.* for xamarin simulator. Please check your network cards for ip addresses and findthe correct one via "cmd.exe" and "ipconfig /all" command.