I'm trying to make authorization in xamarin forms and i dont know how to structure it. I'm using MVVM and for my authorization i wanna use JWT . I want to check if the token is valid then go to certain page . when i put the validation code inside the onappearing method the page is still visible for a very small amount of time and when i put it inside the constructor of the page the navigation doesn't work. How should this authorization should be done?(should i make another transition page with something like an activity indicator ?)
this is the code i use for the token validation
public async Task CheckIfUserIsLoggedIn()
{
if (!await ValidateToken())
{
await _dependencyService.Get<INavigationService>().PushAsync(ViewNames.LOGINVIEW);
}
}
when i put it inside the constructor of the page the navigation
doesn't work.
You can call the push service like this in Main thread:
public partial class MainPage : ContentPage
{
public MainPage()
{
InitializeComponent();
BindingContext = new myViewModel();
CheckIfUserIsLoggedIn();
}
public async void CheckIfUserIsLoggedIn()
{
if (!await ValidateToken())
{
Device.BeginInvokeOnMainThread(async () => {
await _dependencyService.Get<INavigationService>().PushAsync(ViewNames.LOGINVIEW);
});
}
}
}
Related
My aim is to access bindable property across the the App. But My current framework ViewModel Instance create multiple time
My Requirement : I have the cart count in the bottomTray(CheckuoutViewModel) i want to increase the cart count any where in the app page, but in this cart count not update when back click, its only working on forward navigation, the reason behind CheckoutViewModel instance create each and every time. so that i'm try to instant creation at earlier.
Here I'm list out sample ViewModel and calling method
Login ViewModel
Checkuout ViewModel(This view model common for all page)
BaseNavigationViewModel(Its BaseViewModel)
As of now i'm calling when BindinContext each and every time like,
new LoginViewMode(navigation)
new CheckoutViewModel(navigation)
what will do to create all ViewModel instance when app start time like ViewModel Locator?
Im tried
public static ViewModelLocator Locator
{
get { return locator ?? (locator = new ViewModelLocator()); }
}
And ViewModel Locator
public ViewModelLocator()
{
navigation = App.Current.MainPage.Navigation;
}
internal CustomTabBarViewModel CustomTabBarVM
{
get
{
return customTabBarVM ?? (customTabBarVM = new CustomTabBarViewModel(navigation));
}
}
And CustomTabBar.xaml.cs
public CustomTabBar()
{
viewModel = App.Locator.CustomTabBarVM;
InitializeComponent();
BindingContext = viewModel;
}
and Expectation
App.Locator.CustomTabBarVM.BadgeCartCount = OrderObject.Instance.ORDER_OBJECT.Items.Count;
This approach is working fine but it's create some navigation issues
A singleton instance is a common feature of virtually all MVVM frameworks (Prism, FreshMVVM etc). If you aren't using a framework (if you aren't, I would STRONGLY advise you consider using one), below is a solution.
To obtain a single instance of a ViewModel you can use the App class to host the object and access it whenever you need.
Create a public static property of your ViewModel:
public static MyViewModel MyViewModelInstance { get; }
Create an instance in the constructor of the app
public App()
{
InitializeComponent();
MyViewModelInstance = new MyViewModel();
var myPage = new MyPage()
{
BindingContext = MyViewModelInstance
};
var navPage = new NavigationPage(myPage);
MainPage = navPage;
}
Whenever you create a new page, access the shared instance
// This method is just an example of how you might create a new page and wire up the view model
async void GoNextClicked(System.Object sender, System.EventArgs e)
{
var myPage = new MyPage()
{
BindingContext = App.MyViewModelInstance
};
await this.Navigation.PushAsync(myPage);
}
This approach comes with a few caveats, you are creating instances when the app loads not when they are needed (Eagerly loading). So a performance optimisation would be to use Lazy<T> to handle the creation of these objects. However this is logic that has already been written for you in MVVM frameworks, they are there to help you and you should be using them.
Lazy Load
You can save memory and performance at startup by lazy loading the viewmodel, here is this example rewritten to support this pattern:
public static MyViewModel MyViewModelInstance
{
get => _myViewModelInstanceFactory.Value;
}
private static Lazy<MyViewModel> _myViewModelInstanceFactory = new Lazy<MyViewModel>(() => new MyViewModel(), true);
public App()
{
InitializeComponent();
var myPage = new MyPage()
{
BindingContext = MyViewModelInstance
};
var navPage = new NavigationPage(myPage);
MainPage = navPage;
}
Now this object won't be created until it is accessed by your code, and once it has been accessed once it has already been created and will go on to live in memory for the rest of your apps lifecycle.
Axemasta has good answer about re-use of a shared view model instance.
I'll give an alternative approach to the underlying need given in one comment: how to have a static property (so the value is common), and Bind to it when Binding to an instance.
Use this approach if you do want a different CheckoutViewModel for each new page. For example, if there are other properties that should be set up differently, depending on the page.
public class CheckoutViewModel : : INotifyPropertyChanged // or your MVVM library's base class for ViewModels.
{
public static int SharedCount { get; set; }
public void IncrementCount()
{
Count = Count + 1;
}
public int Count {
get => SharedCount;
set {
// Exact code might be simpler if using an MVVM library.
if (SharedCount != value)
{
SharedCount = value;
OnPropertyChanged("Count");
}
}
}
}
}
LIMITATION: This assumes that only the current instance of CheckoutViewModel is visible; if you need to "notify" OTHER Views (update other CheckoutViewModel instances), then you'll need a "publish/subscribe" solution. In Xamarin Forms, one such solution is MessagingCenter.
I have the following AppDelegate which takes quite some time to load:
Syncfusion.ListView.XForms.iOS.SfListViewRenderer.Init();
new Syncfusion.SfNumericUpDown.XForms.iOS.SfNumericUpDownRenderer();
Syncfusion.SfCarousel.XForms.iOS.SfCarouselRenderer.Init();
Syncfusion.XForms.iOS.Buttons.SfSegmentedControlRenderer.Init();
Syncfusion.XForms.iOS.Buttons.SfCheckBoxRenderer.Init();
new Syncfusion.XForms.iOS.ComboBox.SfComboBoxRenderer();
//Syncfusion.XForms.iOS.TabView.SfTabViewRenderer.Init();
new Syncfusion.SfRotator.XForms.iOS.SfRotatorRenderer();
new Syncfusion.SfRating.XForms.iOS.SfRatingRenderer();
new Syncfusion.SfBusyIndicator.XForms.iOS.SfBusyIndicatorRenderer();
What options should I consider when I know some of these components aren't needed for the main screen, but for subscreens?
I am using PRISM, and it appears that every tab is pre-loaded immediately before allowing display or interaction with the end user. What can I do to delay the pre-rendering that the Prism TabView does prior to showing the interface?
Should I use Lazy<T>? What is the right approach?
Should I move these components to another initialization section?
There are a number of ways you could ultimately achieve this, and it all depends on what your real goals are.
If your goal is to ensure that you get to a Xamarin.Forms Page as fast as possible so that you have some sort of activity indicator, that in essence says to the user, "it's ok I haven't frozen, we're just doing some stuff to get ready for you", then you might try creating a "SpashScreen" page where you do additional loading. The setup might look something like the following:
public partial class AppDelegate : FormsApplicationDelegate
{
public override bool FinishedLaunching(UIApplication app, NSDictionary options)
{
global::Xamarin.Forms.Forms.Init();
LoadApplication(new App(new iOSInitializer()));
return base.FinishedLaunching(app, options);
}
}
}
public class iOSInitializer : IPlatformInitializer, IPlatformFinalizer
{
public void RegisterTypes(IContainerRegistry containerRegistry)
{
containerRegistry.RegisterInstance<IPlatformFinalizer>(this);
}
public void Finalize()
{
new Syncfusion.SfNumericUpDown.XForms.iOS.SfNumericUpDownRenderer();
Syncfusion.SfCarousel.XForms.iOS.SfCarouselRenderer.Init();
Syncfusion.XForms.iOS.Buttons.SfSegmentedControlRenderer.Init();
Syncfusion.XForms.iOS.Buttons.SfCheckBoxRenderer.Init();
}
}
public class App : PrismApplication
{
protected override async void OnInitialized()
{
await NavigationService.NavigateAsync("SplashScreen");
}
}
public class SplashScreenViewModel : INavigationAware
{
private IPlatformFinalizer _platformFinalizer { get; }
private INavigationService _navigationService { get; }
public SplashScreenViewModel(INavigationService navigationService, IPlatformFinalizer platformFinalizer)
{
_navigationService = navigationService;
_platformFinalizer = platformFinalizer;
}
public async void OnNavigatedTo(INavigationParameters navigationParameters)
{
_platformFinalizer.Finalize();
await _navigationService.NavigateAsync("/MainPage");
}
}
If you're working with Modules you could take a similar approach though any Modules that would initialize at Startup would still be making that call to Init the renderers before you've set a Page to navigate to. That said, working with Modules does give you a number of benefits here as you only ever would have to initialize things that the app actually requires at that point.
All of that said I'd be surprised if you see much in the way of gain as these Init calls are typically empty methods only designed to prevent the Linker from linking them out... if you aren't linking or have a linker file you could simply instruct the Linker to leave your Syncfusion and other libraries alone.
I'd been searching for a solution to this problem for quite a long time but unfortunately haven't found any nice and elegant way to handle it.
Here are the details:
My MVC 6 application use Areas. Each area has separate directories for the Controllers, Views etc.
Authentication is based on the standard out of the box web application template with user accounts stored in sql server
What I want to achieve is:
When user enters /AreaA/Restricted/Page then he is redirected into /AreaA/Account/Login
When user enters /AreaB/Restricted/Page then he is redirected into /AreaB/Account/Login etc...
Even though I can change the stanard login page redirect from "/Account/Login" into something different like this:
services.Configure<IdentityOptions>(options=> {
options.Cookies.ApplicationCookie.LoginPath =
new Microsoft.AspNet.Http.PathString("/HardcodedAreaName/Account/Login");
});
I am not able to redirect into different actions/login pages for each area.
Prior to MVC 6 I was able to use AuthorizeAttribute with url parameter:
public class CustomAuthorization : AuthorizeAttribute
{
public string Url { get; set; }
// redirect to login page with the original url as parameter.
protected override void HandleUnauthorizedRequest(AuthorizationContext filterContext)
{
filterContext.Result = new RedirectResult(Url + "?returnUrl=" + filterContext.HttpContext.Request.Url.PathAndQuery);
}
}
and then passing the area dependent url by decorating each controller:
[CustomAuthorization(Url = "/Admin/Account/Login"]
public class AdminAreaController : Controller
{ ...
But it does not work anymore :(
Try the following and see if it works (I did try this and it works fine, but not sure If I have covered all scenarios):
The place where you register you CookieAuthentication middleware, you can do something like
app.UseCookieAuthentication(o =>
{
o.LoginPath = "/area1/login1";
o.AuthenticationScheme = "scheme1";
//TODO: set other interesting properties if you want to
});
app.UseCookieAuthentication(o =>
{
o.LoginPath = "/area2/login2";
o.AuthenticationScheme = "scheme2";
//TODO: set other interesting properties if you want to
});
On you controller/action, specify the authentication scheme..example:
[Authorize(ActiveAuthenticationSchemes = "scheme1")]
public IActionResult Test1()
{
return Content("Test1");
}
[Authorize(ActiveAuthenticationSchemes = "scheme2")]
public IActionResult Test2()
{
return Content("Test2");
}
I have an MVC 5 website running using standard forms authentication.
However I need to add an extra step to the user's login process. Once the user has been authenticated we look up whether or not they have access to multiple offices. If they do we need to show them a list of offices and they must choose one.
This is a mandatory step and they cannot be considered logged on until they do it.
Do we need to create our own authentication or should I add a check to a BaseController?
You can extend the implementation of the built-in authentication:
public class OfficeSelectionAuthorizeAttribute : AuthorizeAttribute
{
protected override bool AuthorizeCore(HttpContextBase httpContext)
{
var result = base.AuthorizeCore(httpContext);
if (result)
{
if (IsOfficeSelected())
{
return true;
}
httpContext.Response.RedirectToRoute("OfficeSelection Route");
httpContext.Response.Flush();
}
return false;
}
private bool IsOfficeSelected()
{
//office selection check
}
}
Then you need to use this filter instead of the default one:
[OfficeSelectionAuthorize]
public class AccountController : Controller
{
//action methods
}
Hope everyone is well.
I'm using MVC C# , AspNet.Identities and have a fully functional Account controller.
I recently introduced a basic SignalR Hub to the project, I want to log the user out once he disconnects from the Hub. My idea is to call the LogOff method from the Account Controller.
The Hub is really simple, infact I've taken this from a video by Scott Hanselman if I'm not mistaken. Just the hitCounter part...Now I'm trying to add in the logoff() functionality.
Here's what I've got so far.
[HttpPost]
[ValidateAntiForgeryToken]
public ActionResult LogOff()
{
AuthenticationManager.SignOut();
return RedirectToAction("Welcome", "Home");
}//this is in my account controller
[Authorize]
[HubName("hitCounter")]
public class GameplayHub : Hub
{
private static int intCounter = 0;
public void RecordHit()
{
intCounter += 1;
this.Clients.All.onHitRecorded(intCounter);
}
public override System.Threading.Tasks.Task OnDisconnected(bool stopCalled)
{
Final.Controllers.AccountController obj = new Final.Controllers.AccountController();
intCounter -= 1;
this.Clients.All.onHitRecorded(intCounter);
this.Clients.Caller.onHitRecorded(obj.LogOff());
obj.LogOff();
return base.OnDisconnected(stopCalled);
}
}//this is the hub
<div id="hitCount" style="font-size:50px;"></div>
<script src="~/Scripts/jquery-1.6.4.js"></script>
<script src="~/Scripts/jquery.signalR-2.1.1.js"></script>
<script src="/signalr/hubs"></script>
<script>
$(function() {
var con=$.hubConnection();
var hub=con.createHubProxy('hitCounter');
hub.on('onHitRecorded', function (i) {
$('#hitCount').text(i);
});
con.start(function() {
hub.invoke('recordHit');
});
})
</script>//My view...just shows how many people active at that point...
The amount of people active, shows correctly. What I'm trying to do in my app is, if a user in on 2 tabs, and he closes one, he must be logged off on both.
Any help will be appreciated! Thanks :)
Unfortuntelny it is not going to work. Logging off user is done by removing cookie which has to be done by browser. SignalR runs your disconnected handler after tab was already closed, so you can not tell browser to delete cookie.
The solution that could work is to force redirect to log off page on the second tab opened by user.
Pseudocode:
In SignalR hub:
Task OnDisconnected()
{
var otherTab = FindOtherTabWithUser();
otherTab.forceLogOff();
}
In JavaScript:
forceLogOff = function() { window.location.href = '/logoff'; }