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[Bug] ScrollView content below the fold not rendered on Android #14035

Open damirarh opened 3 years ago

damirarh commented 3 years ago

Description

When content inside a ScrollView dynamically expands, the part that's not visible when it expands isn't rendered on Android. The area is of correct size but everything that was below the fold remains blank.

On iOS it works as expected.

Steps to Reproduce

The attached project reproduces the issue:

  1. When the application loads, click the button until there are enough items that not all of them fit on the screen. On each click, 5 items are added to the list which is used as ItemsSource of a StackLayout inside the ScrollView.
<ScrollView>
    <Grid>
        <Grid.RowDefinitions>
            <RowDefinition Height="50" />
            <RowDefinition Height="*" />
        </Grid.RowDefinitions>
        <Button Text="More items" Clicked="Button_Clicked" />
        <StackLayout Grid.Row="1" BindableLayout.ItemsSource="{Binding Values}">
            <BindableLayout.ItemTemplate>
                <DataTemplate>
                    <Label Padding="10, 0" Text="{Binding}" FontSize="20" />
                </DataTemplate>
            </BindableLayout.ItemTemplate>
        </StackLayout>
    </Grid>
</ScrollView>
private void AddValues()
{
    Values.AddRange(Enumerable.Range(nextItem, 5).Select(i => $"Item {i}"));
    Values = Values.ToList();

    nextItem += 5;
}
  1. Scroll down to see the items that didn't fit on the screen. The page will have the expected size. But the part that was below the fold when the button was clicked is going to be blank. In the screenshot this is manifested as missing items 19 and 20.

Expected Behavior

Content below the fold isn't rendered.

Actual Behavior

Content below the fold should be rendered.

Basic Information

Environment

Show/Hide Visual Studio info ``` Microsoft Visual Studio Enterprise 2019 Version 16.9.2 VisualStudio.16.Release/16.9.2+31112.23 Microsoft .NET Framework Version 4.8.04084 Installed Version: Enterprise ADL Tools Service Provider 1.0 This package contains services used by Data Lake tools ASA Service Provider 1.0 ASP.NET and Web Tools 2019 16.9.688.6828 ASP.NET and Web Tools 2019 ASP.NET Core Razor Language Services 16.1.0.2112521+5741df381174d72f08e3632bb99f52e8635b6a1a Provides languages services for ASP.NET Core Razor. ASP.NET Web Frameworks and Tools 2019 16.9.688.6828 For additional information, visit https://www.asp.net/ Azure App Service Tools v3.0.0 16.9.688.6828 Azure App Service Tools v3.0.0 Azure Data Lake Node 1.0 This package contains the Data Lake integration nodes for Server Explorer. Azure Data Lake Tools for Visual Studio 2.6.3000.0 Microsoft Azure Data Lake Tools for Visual Studio Azure Functions and Web Jobs Tools 16.9.688.6828 Azure Functions and Web Jobs Tools Azure Stream Analytics Tools for Visual Studio 2.6.3000.0 Microsoft Azure Stream Analytics Tools for Visual Studio C# Tools 3.9.0-6.21160.10+59eedc33d35754759994155ea2f4e1012a9951e3 C# components used in the IDE. Depending on your project type and settings, a different version of the compiler may be used. Common Azure Tools 1.10 Provides common services for use by Azure Mobile Services and Microsoft Azure Tools. Extensibility Message Bus 1.2.6 (master@34d6af2) Provides common messaging-based MEF services for loosely coupled Visual Studio extension components communication and integration. Fabric.DiagnosticEvents 1.0 Fabric Diagnostic Events IntelliCode Extension 1.0 IntelliCode Visual Studio Extension Detailed Info Microsoft Azure HDInsight Azure Node 2.6.3000.0 HDInsight Node under Azure Node Microsoft Azure Hive Query Language Service 2.6.3000.0 Language service for Hive query Microsoft Azure Service Fabric Tools for Visual Studio 16.0 Microsoft Azure Service Fabric Tools for Visual Studio Microsoft Azure Stream Analytics Language Service 2.6.3000.0 Language service for Azure Stream Analytics Microsoft Azure Stream Analytics Node 1.0 Azure Stream Analytics Node under Azure Node Microsoft Azure Tools 2.9 Microsoft Azure Tools for Microsoft Visual Studio 2019 - v2.9.40218.1 Microsoft Continuous Delivery Tools for Visual Studio 0.4 Simplifying the configuration of Azure DevOps pipelines from within the Visual Studio IDE. Microsoft JVM Debugger 1.0 Provides support for connecting the Visual Studio debugger to JDWP compatible Java Virtual Machines Microsoft Library Manager 2.1.113+g422d40002e.RR Install client-side libraries easily to any web project Microsoft MI-Based Debugger 1.0 Provides support for connecting Visual Studio to MI compatible debuggers Microsoft Visual Studio Tools for Containers 1.1 Develop, run, validate your ASP.NET Core applications in the target environment. F5 your application directly into a container with debugging, or CTRL + F5 to edit & refresh your app without having to rebuild the container. Mono Debugging for Visual Studio 16.9.7 (df23ba6) Support for debugging Mono processes with Visual Studio. NuGet Package Manager 5.9.0 NuGet Package Manager in Visual Studio. For more information about NuGet, visit https://docs.nuget.org/ ProjectServicesPackage Extension 1.0 ProjectServicesPackage Visual Studio Extension Detailed Info Snapshot Debugging Extension 1.0 Snapshot Debugging Visual Studio Extension Detailed Info SQL Server Data Tools 16.0.62103.10080 Microsoft SQL Server Data Tools ToolWindowHostedEditor 1.0 Hosting json editor into a tool window TypeScript Tools 16.0.30201.2001 TypeScript Tools for Microsoft Visual Studio Visual Basic Tools 3.9.0-6.21160.10+59eedc33d35754759994155ea2f4e1012a9951e3 Visual Basic components used in the IDE. Depending on your project type and settings, a different version of the compiler may be used. Visual F# Tools 16.9.0-beta.21102.9+7ce7132f1459095e635194d09d6f73265352029a Microsoft Visual F# Tools Visual Studio Code Debug Adapter Host Package 1.0 Interop layer for hosting Visual Studio Code debug adapters in Visual Studio Visual Studio Container Tools Extensions 1.0 View, manage, and diagnose containers within Visual Studio. Visual Studio Tools for Containers 1.0 Visual Studio Tools for Containers Visual Studio Tools for Kubernetes 1.0 Visual Studio Tools for Kubernetes VisualStudio.DeviceLog 1.0 Information about my package VisualStudio.Foo 1.0 Information about my package VisualStudio.Mac 1.0 Mac Extension for Visual Studio Xamarin 16.9.000.273 (d16-9@1bba9e0) Visual Studio extension to enable development for Xamarin.iOS and Xamarin.Android. Xamarin Designer 16.9.0.316 (remotes/origin/d16-9@fdbf64026) Visual Studio extension to enable Xamarin Designer tools in Visual Studio. Xamarin Templates 16.9.68 (8e9b569) Templates for building iOS, Android, and Windows apps with Xamarin and Xamarin.Forms. Xamarin.Android SDK 11.2.2.1 (d16-9/877f572) Xamarin.Android Reference Assemblies and MSBuild support. Mono: 5e9cb6d Java.Interop: xamarin/java.interop/d16-9@54f8c24 ProGuard: Guardsquare/proguard/v7.0.1@912d149 SQLite: xamarin/sqlite/3.34.1@daff8f4 Xamarin.Android Tools: xamarin/xamarin-android-tools/d16-9@d210f11 Xamarin.iOS and Xamarin.Mac SDK 14.14.2.5 (3836759d4) Xamarin.iOS and Xamarin.Mac Reference Assemblies and MSBuild support. ```

Build Logs

Screenshots

Blank part of the page after scrolling up.

Reproduction Link

ScrollViewRenderingIssue.zip

Workaround

The missing part of the page is rendered if another render is forced with minimum delay by assigning a value to the bound property, e.g.

Task.Delay(TimeSpan.FromMilliseconds(50)).ContinueWith(_ => Values = Values.ToList());
mashkur commented 3 years ago

Is there any update?

waldo-nl commented 3 years ago

I'm having the same problem when dynamic show/hide content based on a switch.

Example:

<ScrollView>
     <StackLayout>
            <Frame BackgroundColor="#2196F3" Padding="24" CornerRadius="0">
                <Label Text="Welcome to Xamarin.Forms!" HorizontalTextAlignment="Center" TextColor="White" FontSize="36"/>
            </Frame>
        <StackLayout Orientation="Horizontal">
        <Label Text="Show/Hide" />
           <Switch x:Name="showHideSwitch" HorizontalOptions="End"></Switch>
        </StackLayout>

        <Label Text="Start developing now" BindingContext="{x:Reference showHideSwitch}" IsVisible="{Binding IsToggled}" FontSize="64"/>

            <Label Text="1"  FontSize="32" />
            <Label Text="2"  FontSize="32" />
            <Label Text="3"  FontSize="32" />
            <Label Text="4"  FontSize="32" />
            <Label Text="5"  FontSize="32" />
            <Label Text="6"  FontSize="32" />
            <Label Text="7"  FontSize="32" />
            <Label Text="8"  FontSize="32" />
            <Label Text="9"  FontSize="32" />
            <Label Text="10" FontSize="32" />
        </StackLayout>
</ScrollView>
ianthetechie commented 3 years ago

This has been an issue on Android in one for or another for at least a year...

Umer-Mahmood commented 3 years ago

Having the same problem when I change visibility of a frame from false to true inside the scroll view.

Umer-Mahmood commented 3 years ago

Doing myScrollView.ForceLayout(); works for me. I try to make sure this is called only for some very specific conditions to avoid performance issues. For my case it worked quite well.

GuidoNeele commented 3 years ago

danielmeza had a nice workaround https://github.com/xamarin/Xamarin.Forms/issues/14154#issuecomment-828206634

<Grid>
   <ScrollView>
    ...
  </ScrillView>
<Grid>