Bug 22208 - [iOS] OnAppearing Triggers when poping a modal
Summary: [iOS] OnAppearing Triggers when poping a modal
Status: RESOLVED FIXED
Alias: None
Product: Forms
Classification: Xamarin
Component: Forms ()
Version: 1.2.3
Hardware: PC Windows
: Normal normal
Target Milestone: ---
Assignee: Bugzilla
URL:
Depends on:
Blocks:
 
Reported: 2014-08-19 11:38 UTC by Chase Florell
Modified: 2016-03-16 12:23 UTC (History)
14 users (show)

Tags: iOS OnAppearing ac
Is this bug a regression?: ---
Last known good build:

Notice (2018-05-24): bugzilla.xamarin.com is now in read-only mode.

Please join us on Visual Studio Developer Community and in the Xamarin and Mono organizations on GitHub to continue tracking issues. Bugzilla will remain available for reference in read-only mode. We will continue to work on open Bugzilla bugs, copy them to the new locations as needed for follow-up, and add the new items under Related Links.

Our sincere thanks to everyone who has contributed on this bug tracker over the years. Thanks also for your understanding as we make these adjustments and improvements for the future.


Please create a new report on Developer Community or GitHub with your current version information, steps to reproduce, and relevant error messages or log files if you are hitting an issue that looks similar to this resolved bug and you do not yet see a matching new report.

Related Links:
Status:
RESOLVED FIXED

Description Chase Florell 2014-08-19 11:38:05 UTC
simply put, when my root page loads, OnAppearing is triggered... in that method I check if a user has logged in... if they have, I PushModalAsync a LoginPage.

After the user logs in, I pop the modal.

EXPECTED BEHAVIOR:

 - The OnAppearing method of the Parent (Root) page should not trigger a second time when the modal is popped

------

Behavior evident in

  - Xamarin.Forms 1.0.6186
  - Xamarin.Forms 1.2.2.6243
  - Xamarin.Forms 1.2.3.6246-pre1

REPRO

using Xamarin.Forms;

namespace OnAppearingCase
{
    public class App
    {
        public static bool UserHasSuccessfullyLoggedIn;
        public static INavigation Navigation;
        public static Page GetMainPage()
        {
            return new RootPage();
        }
    }

    public class RootPage : MasterDetailPage
    {
        private readonly Label _label;

        public RootPage()
        {
            _label = new Label { Text = "Hello World!", VerticalOptions = LayoutOptions.CenterAndExpand, HorizontalOptions = LayoutOptions.CenterAndExpand };

            Master = new ContentPage { Title = "Master" };
            var detail = new NavigationPage(new ContentPage{Content = _label, Title="Detail"});
            App.Navigation = detail.Navigation;
            Detail = detail;
        }

        protected override async void OnAppearing()
        {
            base.OnAppearing();
            if (!App.UserHasSuccessfullyLoggedIn)
            {
                await App.Navigation.PushModalAsync(new FakeLoginPage());
            }
            else
            {
                // this else should only execute the SECOND time the app starts up
                // AFTER the bool flag is set from some other means.
                // this repro doesn't do that, so this else statement should never be hit.
                _label.Text = "If you're reading this, there's a bug.";
            }
        }
    }

    public class FakeLoginPage : ContentPage
    {
        public FakeLoginPage()
        {
            var button = new Button {Text = "Click Me To Return", VerticalOptions = LayoutOptions.CenterAndExpand, HorizontalOptions = LayoutOptions.CenterAndExpand};
            button.Clicked += (sender, args) =>
            {
                App.UserHasSuccessfullyLoggedIn = true;
                App.Navigation.PopModalAsync();
            };
            Content = button;
        }
    }
}
Comment 1 Parmendra Kumar 2014-08-21 12:08:56 UTC
I have checked this issue and able to reproduce this, To reproduce this issue I
have followed the steps mentioned in Bug Description.
I observed that when root page loads, OnAppearing is triggered.

Screencast: http://www.screencast.com/t/Q6t2LeTmWVQ

Xamarin.Forms 1.2.2.6243

Environment info:

Microsoft Visual Studio Professional 2013
Version 12.0.30723.00 Update 3
Microsoft .NET Framework
Version 4.5.51641

Installed Version: Professional

LightSwitch for Visual Studio 2013   06177-004-0444002-02685
Microsoft LightSwitch for Visual Studio 2013

Team Explorer for Visual Studio 2013   06177-004-0444002-02685
Microsoft Team Explorer for Visual Studio 2013

Visual Basic 2013   06177-004-0444002-02685
Microsoft Visual Basic 2013

Visual C# 2013   06177-004-0444002-02685
Microsoft Visual C# 2013

Visual C++ 2013   06177-004-0444002-02685
Microsoft Visual C++ 2013

Visual F# 2013   06177-004-0444002-02685
Microsoft Visual F# 2013

Visual Studio 2013 Code Analysis Spell Checker   06177-004-0444002-02685
Microsoft® Visual Studio® 2013 Code Analysis Spell Checker

Portions of International CorrectSpell™ spelling correction system © 1993 by Lernout & Hauspie Speech Products N.V. All rights reserved.

The American Heritage® Dictionary of the English Language, Third Edition Copyright © 1992 Houghton Mifflin Company. Electronic version licensed from Lernout & Hauspie Speech Products N.V. All rights reserved.

Windows Phone SDK 8.0 - ENU   06177-004-0444002-02685
Windows Phone SDK 8.0 - ENU

Application Insights Tools for Visual Studio Package   1.0
Application Insights Tools for Visual Studio

ASP.NET and Web Tools   12.3.50717.0
Microsoft Web Developer Tools contains the following components:
Support for creating and opening ASP.NET web projects
Browser Link: A communication channel between Visual Studio and browsers
Editor extensions for HTML, CSS, and JavaScript
Page Inspector: Inspection tool for ASP.NET web projects
Scaffolding: A framework for building and running code generators
Server Explorer extensions for Microsoft Azure Websites
Web publishing: Extensions for publishing ASP.NET web projects to hosting providers, on-premises servers, or Microsoft Azure

ASP.NET Web Frameworks and Tools 2012.2   4.1.21001.0
For additional information, visit http://go.microsoft.com/fwlink/?LinkID=309563

ASP.NET Web Frameworks and Tools 2013   5.2.20703.0
For additional information, visit http://www.asp.net/

Common Azure Tools   1.2
Provides common services for use by Azure Mobile Services and Microsoft Azure Tools.

Microsoft Azure Mobile Services Tools   1.2
Microsoft Azure Mobile Services Tools

NuGet Package Manager   2.8.50313.46
NuGet Package Manager in Visual Studio. For more information about NuGet, visit http://docs.nuget.org/.

Office Developer Tools for Visual Studio 2013 ENU   12.0.30626
Microsoft Office Developer Tools for Visual Studio 2013 ENU

PowerShell Tools   1.2
Provides file classification services using PowerShell

PreEmptive Analytics Visualizer   1.2
Microsoft Visual Studio extension to visualize aggregated summaries from the PreEmptive Analytics product.

SQL Server Data Tools   12.0.30919.1
Microsoft SQL Server Data Tools

Windows Phone 8.1 SDK Integration   1.0
This package integrates the tools for the Windows Phone 8.1 SDK into the menus and controls of Visual Studio.

Workflow Manager Tools 1.0   1.0
This package contains the necessary Visual Studio integration components for Workflow Manager.

Xamarin   3.3.47.0 (0b2a123923812a88ed3091909478dbe9e0111f00)
Visual Studio extension to enable development for Xamarin.iOS and Xamarin.Android
Comment 2 laygr 2014-09-03 13:29:27 UTC
On iOS, the willAppear delegate method is called when you dismiss a modal view. Shouldn't it also be the same for Xamarin.Forms?
Comment 3 Adam Kemp 2014-09-03 23:22:33 UTC
This is the behavior I would expect. If it doesn't behave this way on other platforms then those platforms are wrong. OnAppearing is for when the view is appearing, not just the first time but every time.

If you want to track when it appears the first time then you can use state in your own class to do that. You could also just check state to see if the user is already logged in before presenting a login view.

The behavior described here should not change. It's not a bug.
Comment 4 Chase Florell 2014-09-04 11:55:21 UTC
Adam, that's irrelevant though isn't it? I mean, the basis of the bug report is that it behaves differently between the two platforms... Therefore the approach we would use for one will cause issues for the other.
Comment 5 Adam Kemp 2014-09-04 12:30:59 UTC
I agree. The platforms should behave consistently, and if they're not then something should be fixed. But the behavior described for iOS should be the correct behavior.
Comment 6 Jason Smith [MSFT] 2015-02-05 05:29:01 UTC
This is scheduled into 1.3.5 release, thank you for your patience
Comment 7 Timur Zanagar 2015-03-18 07:17:50 UTC
I think the schedule is changed now? Latest stable version is 1.4.0.
Comment 8 John Miller [MSFT] 2015-07-16 07:44:23 UTC
I would expect this behavior, I don't think it's a bug. 

The inconsistency is a separate issue: https://bugzilla.xamarin.com/show_bug.cgi?id=26479
Comment 9 Jason Smith [MSFT] 2016-03-16 12:23:39 UTC
Thank you for taking the time to submit this report. After reviewing the description of this bug, we no longer believe it affects the current version of Xamarin.Forms. If you are still experiencing the issue after updating your packages, please reopen this report with an attached reproduction.
 
For your convenience, we have created some reproduction best practices viewable here: https://gist.github.com/jassmith/92405c300e54a01dcc6d

Warm regards,
Xamarin Forms Team