ImageCell line Separator not Rendering properly on iOS ListView

[rogerwcpt]

Description

When using an ImageCell in a ListView, and all the properties of the ImageCell are set, specifically the ImageSource, the list item separator is not shown.

Creating a custom ViewCell with a a grid and an Image to emulate a similar layout doesn't have the same issue. The list item separator is rendered fine.

Steps to Reproduce

1. Create ListViewXAML or Code)
2. Create an ImageCell
3. Set the Text, Detail and Image Source

Expected Behavior

All list items should be separated by a grey line separator

Actual Behavior

No list items are separated by a grey line separator. When pulling the listview down to force a repaint of the top list items, the line is drawn only for the first 2 items.

Basic Information

• Version with issue: 3.4.0.1008975
• Last known good version: /
• IDE: Visual Studo for Mac
• Platform Target Frameworks:
  • iOS:
• Nuget Packages: Xamarin.Forms
• Affected Devices:

Screenshots

Reproduction Link

This can be reproduced using the Xamarin University Example XAM280 (Exercise 5 complete)
Or download my source code on github: https://github.com/rogerwcpt/xamarin-forms-list-app

[StephaneDelcroix]

Version with issue: 12.2.1.12

could you point to the Xamarin.Forms version having issue ? thanks

[rogerwcpt]

Version with issue: 12.2.1.12

could you point to the Xamarin.Forms version having issue ? thanks

Hi @StephaneDelcroix,

I found the issue with Xamarin Froms "3.1.0.697729" and "3.4.0.1008975" and "2.4.0.28".
My phone and simulators are running on iOS 12.1.

[rogerwcpt]

I have managed to fix this bug with the following code for the the file:
Xamarin.Forms/Xamarin.Forms.Platform.iOS/Cells/ImageCellRenderer.cs

It seems that the act of forcing running on the main thread when the code is already running on the main thread, causes the line separator to be drawn incorrectly. So first check if you are already on the MainThread.

        async void SetImage(ImageCell cell, CellTableViewCell target)
        {
            var source = cell.ImageSource;

            target.ImageView.Image = null;

            IImageSourceHandler handler;

            if (source != null && (handler = Xamarin.Forms.Internals.Registrar.Registered.GetHandlerForObject<IImageSourceHandler>(source)) != null)
            {
                UIImage uiimage;
                try
                {
                    uiimage = await handler.LoadImageAsync(source).ConfigureAwait(false);
                }
                catch (TaskCanceledException)
                {
                    uiimage = null;
                }

                //Modified code**
                if (NSThread.Current.IsMainThread)
                {
                    SetImage(target, uiimage).Invoke();
                }
                else
                {
                    NSRunLoop.Main.BeginInvokeOnMainThread(SetImage(target, uiimage));
                }
                //***

            }
            else
            {
                target.ImageView.Image = null;
            }
        }

        // Added method for common code 
        static Action SetImage(CellTableViewCell target, UIImage uiimage)
        {
            return () =>
            {
                if (target.Cell != null)
                {
                    target.ImageView.Image = uiimage;
                    target.SetNeedsLayout();
                }
                else
                    uiimage?.Dispose();
            };
        }

[kingces95]

Hm, having troubling building on latest bits.. some issue with the mac build host.. will try again later..

[PureWeen]

@rogerwcpt can you create a PR with your code changes?

[rogerwcpt]

Okay will do.

…

On Sun, Jan 6, 2019 at 4:46 AM Shane Neuville ***@***.***> wrote: @rogerwcpt <https://github.com/rogerwcpt> can you create a PR with your code changes? — You are receiving this because you were mentioned. Reply to this email directly, view it on GitHub <#4711 (comment)>, or mute the thread <https://github.com/notifications/unsubscribe-auth/AMhsT4pJmUZeRywMAMvEZV6JU7riahjUks5vAWOjgaJpZM4ZO04s> .

[rogerwcpt]

I have been testing my fix and its not working in all scenarios. I'm not sure why in some scenarious the ImageCell Rendering is on the background thread, which is where all the problems start.

The solution in my Commit, only works for basic scenarious. This may need to an incremental fix.
Before I create a PR, I'd like to enumerate under which scenarios the fix works and underwhich scenarios the fix doesn't work. eg MVVM, using Code Behind only etc