Navigating from Platform Specific (UWP) PageRenderer and back to PCL Page - xamarin.forms

Question

I have a MainPage in PCL which then navigates to a Platform Specific
Login Page on LoginButton Click Event
The LoginPage is inherited from
platform specific PageRenderer as it needs platform specific
Authentication to Social Providers (Facebook, Google, Twitter,
Microsoft, etc.)
I am using Xamarin.Auth to do the authentication.
Inside the OnElementChanged event of the LoginPage, it instantiates
the OAuth2Authenticator object.
Upon successful instantiation (based
on provider and app details), it needs to call the UI of the specific
provider.
To do that, I call the auth.GetUI where auth is
Xamarin.Auth.OAuth2Authenticator object.
I have two questions:
In UWP, how do I navigate to the provider login UI? More specifically, what is the equivalent in UWP of the following code snippets in iOS and Android? In iOS, the following code is used:
PresentViewController(auth.GetUI(), true, null);
where auth is Xamarin.Auth.OAuth2Authenticator object.
In Android the following is used:
activity.StartActivity(auth.GetUI(activity));
I am looking for the equivalent code in UWP. Please bear in mind that these calls are made from the LoginPage which is derived from Platform specific PageRenderer
How do I navigate back to my MainPage (which is in PCL) upon successful authentication?
The code is based off of a sample from the following source:
http://www.c-sharpcorner.com/article/oauth-login-authenticating-with-identity-provider-in-xamarin-forms/
Here is my code for the LoginPage:
using System;
using Valufy;
using Xamarin.Forms.Platform.UWP;
using System.ComponentModel;
using Valufy.UWP;
using Valufy.AuthConfiguration;
using Xamarin.Forms;
[assembly: ExportRenderer(typeof(ProviderLoginPage), typeof(LoginRenderer))]
namespace Valufy.UWP
{
class LoginRenderer: PageRenderer
{
protected override void OnElementChanged (ElementChangedEventArgs<Xamarin.Forms.Page> e)
{
base.OnElementChanged(e);
//Get and Assign ProviderName from ProviderLoginPage
ProviderLoginPage loginPage = (ProviderLoginPage)Element;
string providername = loginPage.ProviderName;
//Create OauthProviderSetting class with Oauth Implementation .Refer Step 6
OAuthProviderSetting oauth = new OAuthProviderSetting();
Xamarin.Auth.OAuth2Authenticator auth = oauth.LoginWithProvider(providername);
// After facebook,google and all identity provider login completed
auth.Completed += Auth_Completed;
Type page_type = auth.GetUI();
//////THIS IS WHERE I AM STUCK...HOW DO I GO TO THE PROVIDER AUTH UI ////////////
//this.Frame.Navigate(page_type, auth);
//parentPage.Navigation.PushModalAsync(auth.GetUI());
}
}
private void Auth_Completed(object sender, Xamarin.Auth.AuthenticatorCompletedEventArgs e)
{
if (e.IsAuthenticated)
{
OAuthConfig.User = new UserDetails();
// Get and Save User Details
OAuthConfig.User.Token = e.Account.Properties["oauth_token"];
OAuthConfig.User.TokenSecret = e.Account.Properties["oauth_token_secret"];
OAuthConfig.User.TwitterId = e.Account.Properties["user_id"];
OAuthConfig.User.ScreenName = e.Account.Properties["screen_name"];
/////NOW, HOW GO I GO BACK TO THE CALLING PAGE IN PCL ///////////////////
}
else
{
// The user cancelled
/////NOW, HOW GO I GO BACK TO THE CALLING PAGE IN PCL ///////////////////
}
}
}
}

Answer 1

Here is the code to navigate to the provider login for UWP:
WindowsPage windowsPage = new WindowsPage();
_frame = windowsPage.Frame;
if (_frame == null)
{
_frame = new Windows.UI.Xaml.Controls.Frame
{
Language = global::Windows.Globalization.ApplicationLanguages.Languages[0]
};
windowsPage.Content = _frame;
SetNativeControl(windowsPage);
}
Type pageType = auth.GetUI();
_frame.Navigate(pageType, auth);
To navigate back to my page upon successful authentication, here is the code:
private async void Auth_Completed(object sender, Xamarin.Auth.AuthenticatorCompletedEventArgs e)
{
if (e.IsAuthenticated)
{
var request = new OAuth2Request("GET", new Uri("https://login.microsoftonline.com/common/oauth2/V2.0/token?oauth2_access_token=" + e.Account.Properties["access_token"]), null, e.Account);
try
{
string response = await MSGetUserInfo(e.Account);
}
catch (System.OperationCanceledException)
{
}
catch (Exception ex)
{
}
this.Element.Navigation.PushModalAsync(new MainPage());
}
else
{
// The user cancelled
}
}

Answer 2

1- In UWP, how do I navigate to the provider login UI
You need to create a UWP Page object, the same object you are will use to display in the renderer is the one you will use to do the navigation.
Type page_type = auth.GetUI();
page = new MyUWPLoginPage();
page.Frame.Navigate(page_type, auth);
2- How do I navigate back to my MainPage (which is in PCL) upon successful authentication?
There are many ways to do this, the easiest one is creating a public method in your ProviderLoginPage class and from the renderer classes call this method and pass-in the parameters.
public class ProviderLoginPage: ContentPage
{
......
public void AuthenticationCompleted(object sender, Xamarin.Auth.AuthenticatorCompletedEventArgs e)
{
// Do your logic
}
}
In your Renderer using the Element:
private void Auth_Completed(object sender, Xamarin.Auth.AuthenticatorCompletedEventArgs e)
{
var xamElement = Element as ProviderLogin;
xamElement?.AuthenticationCompleted(sender, e);
}
Move all the logic to the PCL class so you don't have to repeat it on each renderer.
This should help.