Xamarin Forms: System.NullReferenceException in AppDelegate - xamarin

Question

Hi tried to compile my app for the first time for IOS but I got this:
System.NullReferenceException: Object reference not set to an instance of an object
in the AppDelegate.
It stops in this line :return base.FinishedLaunching(app, options);
I'm relative new into xamarin so I am sorry for my unknowingness.
Here is my complete AppDelegate:
using System;
using System.Collections.Generic;
using System.Linq;
using System.Drawing;
using System.Globalization;
using System.IO;
using Flex;
using Foundation;
using UIKit;
using Xamarin.Forms;
using Xamarin.Forms.Platform.iOS;
using System.Xml.Linq;
namespace dpsApp.iOS
{
[Register("AppDelegate")]
public partial class AppDelegate : global::Xamarin.Forms.Platform.iOS.FormsApplicationDelegate
{
public override bool FinishedLaunching(UIApplication app, NSDictionary options)
{
global::Xamarin.Forms.Forms.Init();
Rg.Plugins.Popup.Popup.Init();
FlexButton.Init();
LoadApplication(new App());
return base.FinishedLaunching(app, options);
}
}
}
So here is my MainPage XAML:
`
<StackLayout WidthRequest="10000">
<StackLayout x:Name="LogoStack" BackgroundColor="White">
<Image x:Name="Image"
Source="a.png"
HeightRequest="120"
WidthRequest="120"
HorizontalOptions="Center">
<Image.GestureRecognizers>
<TapGestureRecognizer Tapped="EasterCount"/>
</Image.GestureRecognizers>
</Image>
</StackLayout>
<StackLayout x:Name="StackList" IsVisible="True" HeightRequest="3000">
<ListView x:Name="PageList"
HasUnevenRows="True"
ItemTapped="Link_ItemTapped"
HeightRequest="25"
BackgroundColor="White">
<ListView.ItemTemplate>
<DataTemplate>
<ViewCell>
<StackLayout Orientation="Horizontal" Margin="0,0,0,0" BackgroundColor="#e7e7e7" HeightRequest="65" Padding="0">
<Grid x:Name="DeleteStack" VerticalOptions="CenterAndExpand" BackgroundColor="White" HorizontalOptions="FillAndExpand" >
<Grid.ColumnDefinitions>
<ColumnDefinition Width="*" />
<ColumnDefinition Width="50" />
</Grid.ColumnDefinitions>
<Grid.RowDefinitions>
<RowDefinition Height="28" />
<RowDefinition Height="22" />
<RowDefinition Height="1" />
</Grid.RowDefinitions>
<Label Grid.Column="0" Grid.Row="0" Text="{Binding Title}" LineBreakMode="TailTruncation" FontSize="25" Margin="20,0,0,0"/>
<Label Grid.Column="0" Grid.Row="1" Text="{Binding Link}" LineBreakMode="TailTruncation" FontSize="17" Margin="20,0,0,0"/>
<Image Margin="0,0,20,0"
IsVisible="{Binding IsVisible}"
Grid.Column="1"
Grid.Row="0"
Grid.RowSpan="2"
x:Name="DeleteButton"
Source="delete.png"
VerticalOptions="Center"
HeightRequest="20"
HorizontalOptions="Center"/>
</Grid>
</StackLayout>
</ViewCell>
</DataTemplate>
</ListView.ItemTemplate>
</ListView>
</StackLayout>
<StackLayout x:Name="FirstTimeOpenStack" HorizontalOptions="Center">
<Label Text="Please tap on the plus icon in the top right corner to add a website" />
</StackLayout>
</StackLayout>

Answer 1

Your App Delegate looks ok. You have an unhandled exception somewhere in the App() you are launching.
Here is one way to capture unhandled exceptions:
namespace WiFiVisualPager.iOS
{
// The UIApplicationDelegate for the application. This class is responsible for launching the
// User Interface of the application, as well as listening (and optionally responding) to
// application events from iOS.
[Register("AppDelegate")]
public partial class AppDelegate : global::Xamarin.Forms.Platform.iOS.FormsApplicationDelegate
{
//
// This method is invoked when the application has loaded and is ready to run. In this
// method you should instantiate the window, load the UI into it and then make the window
// visible.
//
// You have 17 seconds to return from this method, or iOS will terminate your application.
//
public override bool FinishedLaunching(UIApplication app, NSDictionary options)
{
AppDomain.CurrentDomain.UnhandledException += CurrentDomainOnUnhandledException;
TaskScheduler.UnobservedTaskException += TaskSchedulerOnUnobservedTaskException;
global::Xamarin.Forms.Forms.Init();
DisplayCrashReport();
LoadApplication(new App());
return base.FinishedLaunching(app, options);
}
#region [Error handling]
//Credit: Peter Norman.
//https://peterno.wordpress.com/2015/04/15/unhandled-exception-handling-in-ios-and-android-with-xamarin/
//Minor compile fixes by David McCurley.
private static void TaskSchedulerOnUnobservedTaskException(object sender, UnobservedTaskExceptionEventArgs unobservedTaskExceptionEventArgs)
{
var newExc = new Exception("TaskSchedulerOnUnobservedTaskException", unobservedTaskExceptionEventArgs.Exception);
LogUnhandledException(newExc);
}
private static void CurrentDomainOnUnhandledException(object sender, UnhandledExceptionEventArgs unhandledExceptionEventArgs)
{
var newExc = new Exception("CurrentDomainOnUnhandledException", unhandledExceptionEventArgs.ExceptionObject as Exception);
LogUnhandledException(newExc);
}
internal static void LogUnhandledException(Exception exception)
{
try
{
const string errorFileName = "Fatal.log";
var libraryPath = System.Environment.GetFolderPath(Environment.SpecialFolder.Resources); // iOS: Environment.SpecialFolder.Resources
var errorFilePath = Path.Combine(libraryPath, errorFileName);
var errorMessage = String.Format("Time: {0}\r\nError: Unhandled Exception\r\n{1}",
DateTime.Now, exception.ToString());
File.WriteAllText(errorFilePath, errorMessage);
// Log to Android Device Logging.
//Android.Util.Log.Error("Crash Report", errorMessage);
}
catch
{
// just suppress any error logging exceptions
}
}
/// <summary>
// If there is an unhandled exception, the exception information is diplayed
// on screen the next time the app is started (only in debug configuration)
/// </summary>
[Conditional("DEBUG")]
private static void DisplayCrashReport()
{
const string errorFilename = "Fatal.log";
var libraryPath = Environment.GetFolderPath(Environment.SpecialFolder.Resources);
var errorFilePath = Path.Combine(libraryPath, errorFilename);
if (!File.Exists(errorFilePath))
{
return;
}
var errorText = File.ReadAllText(errorFilePath);
var alertView = new UIAlertView("Crash Report", errorText, null, "Close", "Clear") { UserInteractionEnabled = true };
alertView.Clicked += (sender, args) =>
{
if (args.ButtonIndex != 0)
{
File.Delete(errorFilePath);
}
};
alertView.Show();
}
#endregion
}
}