Fix the OnNavigatedTo event and the OnAppearing event to return the ScrollToAsync method call #16619

cat0363 · 2023-08-09T06:43:46Z

This PR fixes the problem that the call does not return when the ScrollToAsync method is
called at the timing of OnNavigatedTo, OnAppearing events.

Description of Change

If the ScrollToAsync method is called in the OnNavigatedTo or OnAppearing event, the Handler is null
at this point, so I added code to handle the scroll request in the Loaded event.

[src\Controls\src\Core\ScrollView\ScrollView.cs]

void OnScrollToRequested(ScrollToRequestedEventArgs e)
{
    CheckTaskCompletionSource();
    ScrollToRequested?.Invoke(this, e);

    if (Handler is not null)
    {
        Handler.Invoke(nameof(IScrollView.RequestScrollTo), ConvertRequestMode(e).ToRequest());
    }
    else
    {
        Loaded += (sender, args) =>
        {
            Dispatcher.Dispatch(() =>
            {
                Handler?.Invoke(nameof(IScrollView.RequestScrollTo), ConvertRequestMode(e).ToRequest());
            });
        };
    }
}

On Windows, the ViewChanged event doesn't fire until the ScrollView's position is updated, so I added code to call the ScrollFinish method if the requested scroll position is the same as the current scroll position when processing a scroll request.

[src\Core\src\Handlers\ScrollView\ScrollViewHandler.Windows.cs]

public static void MapRequestScrollTo(IScrollViewHandler handler, IScrollView scrollView, object? args)
{
    if (args is ScrollToRequest request)
    {
        if (handler.PlatformView.HorizontalOffset == request.HorizontalOffset &&
            handler.PlatformView.VerticalOffset == request.VerticalOffset)
        {
            handler.VirtualView.ScrollFinished();
        }
        else
        {
            handler.PlatformView.ChangeView(request.HorizontalOffset, request.VerticalOffset, null, request.Instant);
        }
    }
}

Issues Fixed

Fixes #15387

I used the following code for testing.

https://github.com/cat0363/Maui-IssueScrollToAsync2.git

The following log is output to the Editor before and after calling the ScrollToAsync method.

    txtLog.Text += ("Before ScrollToAsync" + Environment.NewLine);
    await svTestItem.ScrollToAsync(0, 200, false);
    txtLog.Text += ("After ScrollToAsync" + Environment.NewLine);

Below is the execution result.

[iOS]

[OnNavigatedTo]	[OnAppearing]
iPhone.14.iOS.16.4.2023-08-09.12-08-31.mp4	iPhone.14.iOS.16.4.2023-08-09.12-43-59.mp4

[Android]

[OnNavigatedTo]	[OnAppearing]
Android.Emulator.-.pixel_2_-_api_30_5554.2023-08-09.12-11-58.mp4	Android.Emulator.-.pixel_2_-_api_30_5554.2023-08-09.12-47-30.mp4

[Windows]

[OnNavigatedTo]	[OnAppearing]
2023-08-09.12-05-21.mp4	2023-08-09.12-26-53.mp4

You can see that the ScrollToAsync method call is returned in the OnNavigatedTo event and OnAppearing event on all platforms.
The log is already displayed when the screen is started, but it is the log when the ScrollToAsync method is called in the OnNavigateTo event and OnAppearing event that is called when the screen is displayed for the first time.

ghost · 2023-08-09T06:43:54Z

Hey there @cat0363! Thank you so much for your PR! Someone from the team will get assigned to your PR shortly and we'll get it reviewed.

jfversluis · 2023-08-09T13:26:15Z

/azp run MAUI-UITests-public

azure-pipelines · 2023-08-09T13:26:26Z

Azure Pipelines successfully started running 1 pipeline(s).

cat0363 · 2023-08-10T05:37:58Z

I wrote the unit test code.
This is my first time writing test code that uses NavigationPage, so if there are any mistakes, could you point them out?

azure-pipelines · 2023-08-15T10:24:36Z

Azure Pipelines successfully started running 1 pipeline(s).

rmarinho · 2023-08-21T15:35:21Z

@cat0363 can you get the latest changes from main please? I think this could have been fixed by 5af60d3

cat0363 · 2023-08-22T02:39:56Z

@rmarinho , Thank you for letting me know.
I got the latest for main and verified it.

Below are the verification results.

[iOS]

[OnNavigatedTo]	[OnAppearing]
iPhone.14.iOS.16.4.2023-08-22.11-34-15.mp4	iPhone.14.iOS.16.4.2023-08-22.11-37-28.mp4

On iOS, calling the ScrollToAsync method in the OnNavigatedTo and OnAppearing events when the screen is first displayed does not work as intended.

[Android]

[OnNavigatedTo]	[OnAppearing]
Android.Emulator.-.pixel_2_-_api_30_5554.2023-08-22.10-47-28.mp4	Android.Emulator.-.pixel_2_-_api_30_5554.2023-08-22.10-42-11.mp4

On Android, calling the ScrollToAsync method in the OnNavigatedTo and OnAppearing events when the screen is first displayed does not work as intended.

[Windows]

[OnNavigatedTo]	[OnAppearing]
2023-08-22.10-28-36.mp4	2023-08-22.10-26-18.mp4

On Windows, calling the ScrollToAsync method in the OnNavigatedTo and OnAppearing events when the screen is first displayed does not work as intended. Calling the ScrollToAsync method in the OnAppearing event when transitioning from another screen does not work as intended.

All in all, the result was not what I expected.

The PR I created shows that the ScrollToAsync method works as intended even when the screen is displayed for the first time.
I expected the ScrollToAsync method to work as intended when the screen first appeared, and not when it was navigated to from another screen.

cat0363 · 2023-09-12T08:31:36Z

With 5af60d3, the problem is still there. Is there any other solution?
A stale tag was added, but the problem is still there.

cat0363 · 2023-12-15T04:35:05Z

Even with .NET 8, the problem continues to occur.
If you wait synchronously for the ScrollToAsync method inside the OnNavigatedTo event, it will remain blocked.

cat0363 · 2024-01-12T03:27:00Z

@rmarinho , As far as I investigated, the method call does not finish only if the ScrollToAsync method is called when the ScrollView's size is not determined.
Calling the ScrollToAsync method when the height and width of the ScrollView are 0 and not determined will fail.
I hope this will give you a hint on how to fix it.

rmarinho · 2024-01-12T12:12:16Z

Can you rebase on main I will pull and take a look

cat0363 · 2024-01-15T05:44:12Z

Modify the previous code and upload it again.
Please wait a moment now.

cat0363 · 2024-01-15T09:09:29Z

I made some changes today, but I'll revert to the latest version of main.
After applying the latest version of main, both Android and iOS no longer wait forever after calling the ScrollToAsync method, but on Android, the screen does not scroll correctly the first time it is displayed. On Android, the scroll position remains at (0,0).

It's probably the same problem as the one below.
#14594

cat0363 · 2024-01-16T08:18:17Z

The latest code verification results for main are listed below.

On Windows, if the call to the ScrollToAsync method does not change the position of the ScrollBar, the call to the ScrollToAsync method does not finish. Therefore, in addition to the latest source code for main, you will need:

[src\Core\src\Handlers\ScrollView\ScrollViewHandler.Windows.cs]

public static void MapRequestScrollTo(IScrollViewHandler handler, IScrollView scrollView, object? args)
{
    if (args is ScrollToRequest request)
    {
        if (handler.PlatformView.HorizontalOffset == request.HorizontalOffset &&
            handler.PlatformView.VerticalOffset == request.VerticalOffset)
        {
            handler.VirtualView.ScrollFinished();
        }
        else
        {
            handler.PlatformView.ChangeView(request.HorizontalOffset, request.VerticalOffset, null, request.Instant);
        }
    }
}

On iOS, calling the ScrollToAsync method within the OnNavigatedTo, OnAppearing events works as intended.

On Android, calling the ScrollToAsync method within the OnNavigatedTo, OnAppearing event does not work as intended only on first appearance.

PureWeen · 2025-08-16T17:25:58Z

/azp run

azure-pipelines · 2025-08-16T17:26:17Z

Azure Pipelines successfully started running 3 pipeline(s).

jfversluis · 2025-11-27T16:09:46Z

/rebase

…crollToAsync method call # Conflicts: # src/Controls/src/Core/ScrollView/ScrollView.cs

jfversluis · 2025-11-27T19:24:13Z

/azp run MAUI-public

azure-pipelines · 2025-11-27T19:24:26Z

Azure Pipelines successfully started running 1 pipeline(s).

jfversluis · 2025-11-28T18:54:33Z

/azp run MAUI-DeviceTests-public

azure-pipelines · 2025-11-28T18:54:45Z

Azure Pipelines successfully started running 1 pipeline(s).

jfversluis · 2025-12-01T09:39:09Z

The test seems to fail on Android and that even crashes the test suite. I think the fix is good though.

ghost added the community ✨ Community Contribution label Aug 9, 2023

jsuarezruiz added the area-controls-scrollview ScrollView label Aug 9, 2023

jsuarezruiz requested a review from hartez August 9, 2023 13:42

samhouts added this to the Under Consideration milestone Aug 15, 2023

Eilon added the area-layout StackLayout, GridLayout, ContentView, AbsoluteLayout, FlexLayout, ContentPresenter label Aug 15, 2023

samhouts added the stale Indicates a stale issue/pr and will be closed soon label Sep 11, 2023

hartez requested review from rmarinho and removed request for hartez January 10, 2024 21:08

cat0363 requested a review from a team as a code owner January 15, 2024 04:33

cat0363 requested a review from tj-devel709 January 15, 2024 04:33

Eilon removed the area-layout StackLayout, GridLayout, ContentView, AbsoluteLayout, FlexLayout, ContentPresenter label May 14, 2024

PureWeen removed this from the Under Consideration milestone Aug 2, 2024

PureWeen force-pushed the fix-15387 branch from 6bf9113 to 00adbd6 Compare August 16, 2025 17:25

jfversluis added this to the .NET 10 SR1 milestone Oct 21, 2025

PureWeen modified the milestones: .NET 10 SR1, .NET 10.0 SR2 Nov 4, 2025

cat0363 added 2 commits November 27, 2025 16:10

Fix the OnNavigatedTo event and the OnAppearing event to return the S…

8e6bd53

…crollToAsync method call # Conflicts: # src/Controls/src/Core/ScrollView/ScrollView.cs

Add unit tests

39d4332

github-actions bot force-pushed the fix-15387 branch from 00adbd6 to 39d4332 Compare November 27, 2025 16:10

jfversluis modified the milestones: .NET 10.0 SR2, .NET 10.0 SR3 Dec 2, 2025

Fix the OnNavigatedTo event and the OnAppearing event to return the ScrollToAsync method call #16619

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cat0363 commented Aug 9, 2023

Description of Change

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