How to display an error message in Xamarin PCL - xamarin

Question

I'm doing a simple try/catch (in a PCL project) to validate the users connection to the app, but I cant seem to find the DisplayAlert() method used in the Xamarin websites example.
Here are my usings:
using Newtonsoft.Json;
using System;
using System.Collections.Generic;
using System.Linq;
using System.Net.Http;
using System.Net.Http.Headers;
using System.Text;
using System.Threading.Tasks;
using System.Windows.Input;
using System.Security;
using System.Diagnostics;
Here is the code:
public async Task Connexion()
{
// on met en place un try catch pour déceler toute erreur dans la procédure de connexion
try
{
// url de récupération du json de l'acteur
string urlActeur = "http://10.0.0.5/ppe3JoJuAd/gsbAppliFraisV2/webservices/w_visiteur.php" + "?" + "login=" + Login + "&" + "pass=" + Pass;
//instanciation du client http qui envoi un header json
HttpClient clientActeur = new HttpClient();
clientActeur.DefaultRequestHeaders.Accept.Clear();
clientActeur.DefaultRequestHeaders.Accept.Add(new MediaTypeWithQualityHeaderValue("application/json"));
//réponse à la requête Http
var response = await clientActeur.GetAsync(urlActeur);
var json = response.Content.ReadAsStringAsync().Result;
var acteurJson = JsonConvert.DeserializeObject<ActeurJson>(json);
//on vérifie les informations de connexion du user (ici cela se ait avec oldMdp car pas d'implémentation du SHA1 actuellement en Xamarin, auquel cas nous auions converti le contenu du champ pass en sha1 puis vérification avec le champ mdp de l'acteur)
if (acteurJson.Acteur.login == login && acteurJson.Acteur.mdp == acteurJson.Acteur.oldMdp)
App.Current.MainPage = new VisitePage();
}
catch
{
await DisplayAlert()//intelisense does not find the using or the required dll
}
where should I look or what should I do to display the message ?

Answer 1

You shouldn't do a DisplayAlert from a Task. You should relay a message back to the calling class about a failure or just raise the exception to the calling class. For a task to come back into the UI and raise a message is bad.
Also your use of HttpClient is off. HttpClient is meant to be used as a singleton method. Try and create one per project or modules as a static singleton.
All that being said, try this:
public class ConnexionHelper
{
public async Task Connexion()
{
try
{
System.Diagnostics.Debug.WriteLine("trying stuff");
}
catch( Exception ex )
{
Xamarin.Forms.Page ourPage = App.Current.MainPage.Navigation.NavigationStack.LastOrDefault();
if (ourPage != null)
{
await ourPage.DisplayAlert("eeek", "error has occurrred", "not ok");
}
}
}

Answer 2

Application.Current.MainPage.DisplayAlert should works

Answer 3

Its better to add userdialogs plugin for xamarin. It comes up with different type of alerts,toasts etc for showing messages in the UI. Also it gives a better UI.
You can install the userdialogs from https://www.nuget.org/packages/Acr.UserDialogs/
After installing, you can show alert as follows:
UserDialogs.Instance.Alert("","","OK">);
You can also display alert as toasts.

Answer 4

You can display toast message using Toasts.Forms.Plugin
Setup
In your iOS, Android, WinRT and UWP projects please call:
DependencyService.Register<ToastNotification>(); // Register your dependency
ToastNotification.Init();
// If you are using Android you must pass through the activity
ToastNotification.Init(this);
If you are using Xamarin Forms, you must do this AFTER your call to Xamarin.Forms.Init();
Permissions
In iOS you must request permission to show local notifications first since it is a user interrupting action.
// Request Permissions
if (UIDevice.CurrentDevice.CheckSystemVersion(10, 0))
{
// Request Permissions
UNUserNotificationCenter.Current.RequestAuthorization(UNAuthorizationOptions.Alert | UNAuthorizationOptions.Badge | UNAuthorizationOptions.Sound, (granted, error) =>
{
// Do something if needed
});
}
else if (UIDevice.CurrentDevice.CheckSystemVersion(8, 0))
{
var notificationSettings = UIUserNotificationSettings.GetSettingsForTypes(
UIUserNotificationType.Alert | UIUserNotificationType.Badge | UIUserNotificationType.Sound, null);
app.RegisterUserNotificationSettings(notificationSettings);
}
Usage
Use dependency service in order to resolve IToastNotificator.
var notificator = DependencyService.Get<IToastNotificator>();
var options = new NotificationOptions()
{
Title = "Title",
Description = "Description"
};
var result = await notificator.Notify(options);
The result that is returned is a NotificationResult with an Action inside with one of the following values.
[Flags]
public enum NotificationAction
{
Timeout = 1, // Hides by itself
Clicked = 2, // User clicked on notification
Dismissed = 4, // User manually dismissed notification
ApplicationHidden = 8, // Application went to background
Failed = 16 // When failed to display the toast
}
If you want the Clicked NotificationAction you must set IsClickable = true in the NotificationOptions.