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[Bug] ScrollView and Grid with Star row height cut off invisible part #14220

Open RenaudAvenas opened 3 years ago

RenaudAvenas commented 3 years ago

Description

When a grid is resized because a child in a row (star height) changed it size (IsVisible becomes true by example) then the parent ScrollView can scroll to this child but it is cut off.

Steps to Reproduce

  1. Create a page with a ScrollView
  2. Insert a grid
  3. Put a child with IsVisible property to false and heightRequest to more than your screen height
  4. Use a button to make child become visible
  5. Scroll to bottom

Expected Behavior

The child must be drawn

Actual Behavior

The child is cut off

Basic Information

Environment

Show/Hide Visual Studio info ``` Microsoft Visual Studio Enterprise 2019 (2) Version 16.8.4 VisualStudio.16.Release/16.8.4+30907.101 Microsoft .NET Framework Version 4.8.03752 Version installée : Enterprise Visual C++ 2019 00435-60000-00000-AA190 Microsoft Visual C++ 2019 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 16.8.557.25636 ASP.NET and Web Tools 2019 ASP.NET Core Razor Language Services 16.1.0.2052803+84e121f1403378489b842e1797df2f3f5a49ac3c Provides languages services for ASP.NET Core Razor. ASP.NET Web Frameworks and Tools 2019 16.8.557.25636 Pour plus d'informations, visitez https://www.asp.net/ Assistants Microsoft Visual C++ 1.0 Assistants Microsoft Visual C++ Azure Data Lake Node 1.0 This package contains the Data Lake integration nodes for Server Explorer. 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Microsoft JVM Debugger 1.0 Provides support for connecting the Visual Studio debugger to JDWP compatible Java Virtual Machines Microsoft MI-Based Debugger 1.0 Provides support for connecting Visual Studio to MI compatible debuggers Mono Debugging for Visual Studio 16.8.43 (00471f8) Support for debugging Mono processes with Visual Studio. Outils Azure App Service v3.0.0 16.8.557.25636 Outils Azure App Service v3.0.0 Outils C# 3.8.0-5.20604.10+9ed4b774d20940880de8df1ca8b07508aa01c8cd Composants C# utilisés dans l'IDE. Selon votre type de projet et vos paramètres, une version différente du compilateur peut être utilisée. Outils TypeScript 16.0.21016.2001 Outils TypeScript pour Microsoft Visual Studio Outils Visual Basic 3.8.0-5.20604.10+9ed4b774d20940880de8df1ca8b07508aa01c8cd Composants Visual Basic utilisés dans l'IDE. Selon votre type de projet et vos paramètres, une version différente du compilateur peut être utilisée. 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Appuyez sur F5 pour exécuter votre application directement dans un conteneur avec débogage ou sur CTRL+F5 pour modifier et actualiser votre application sans avoir à recréer le conteneur. Visual Studio Tools pour Kubernetes 1.0 Visual Studio Tools pour Kubernetes VisualStudio.DeviceLog 1.0 Informations sur mon paquet VisualStudio.Foo 1.0 Information about my package VisualStudio.Mac 1.0 Mac Extension for Visual Studio Xamarin 16.8.000.261 (d16-8@bb99248) Extension Visual Studio permettant de développer pour Xamarin.iOS et Xamarin.Android. Xamarin Designer 16.8.0.507 (remotes/origin/d16-8@e87b24884) Extension Visual Studio pour activer les outils Xamarin Designer dans Visual Studio. Xamarin Templates 16.8.112 (86385a3) Templates for building iOS, Android, and Windows apps with Xamarin and Xamarin.Forms. Xamarin.Android SDK 11.1.0.26 (d16-8/a36ce73) Xamarin.Android Reference Assemblies and MSBuild support. Mono: 5e9cb6d Java.Interop: xamarin/java.interop/d16-8@79d9533 ProGuard: Guardsquare/proguard/proguard6.2.2@ebe9000 SQLite: xamarin/sqlite/3.32.1@1a3276b Xamarin.Android Tools: xamarin/xamarin-android-tools/d16-8@2fb1cbc Xamarin.iOS and Xamarin.Mac SDK 14.8.0.3 (c51fabee8) Xamarin.iOS and Xamarin.Mac Reference Assemblies and MSBuild support. ```

Screenshots

Reproduction Link

Type this code in MainPage of Empty Xamarin.Forms application (5.0.0.2012) and implement Button_Clicked to invert IsVisible value of the BlueRectangle : ` <?xml version="1.0" encoding="utf-8" ?> <ContentPage xmlns="http://xamarin.com/schemas/2014/forms" xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml" x:Class="ScrollBug.MainPage">

<ScrollView>
    <Grid
        RowDefinitions="400,Auto,*">

        <Rectangle
            Background="Red"
            HeightRequest="400" />
        <Button
            Grid.Row="1"
            Text="Hide/Show blue rectangle"
            Clicked="Button_Clicked" />
        <Rectangle
            Grid.Row="2"
            x:Name="BlueRectangle"
            IsVisible="False"
            HeightRequest="500"
            Background="Blue" />
    </Grid>
</ScrollView>

`

Workaround

Call InvalidateMesure on child

azrinsani commented 3 years ago

I think this is expected. That's why grid is the recommended layout vs stacklayout. Stack layout initiates the invalidatemeasure call on each state change.

Conclusions

A child of a stacklayout will always cause a full layout cycle, there’s no way a StackLayout can short circuit this cycle. A child of a Grid with that’s inside rows and columns with static or star widths AND the LayoutOptions are set to Fill, are fully constrained which means that the invalidation cycle will be stopped at that child view. In order to have children of a Grid change layout dynamically they need to be a child of another View which is fully constrained. (As per the Grid sample).

Read more here:

https://michaelridland.com/xamarin/hacking-the-xamarin-forms-layout-system-for-fun-and-profit/

RenaudAvenas commented 3 years ago

Images are better than words ^^ : Screen1 After the button clicked : Screen2 After scrolling down : Screen3

Expected : Screen4

RenaudAvenas commented 3 years ago

The code to reproduce : ScrollBug.zip

RenaudAvenas commented 3 years ago

I think this is expected. That's why grid is the recommended layout vs stacklayout. Stack layout initiates the invalidatemeasure call on each state change.

Conclusions

A child of a stacklayout will always cause a full layout cycle, there’s no way a StackLayout can short circuit this cycle. A child of a Grid with that’s inside rows and columns with static or star widths AND the LayoutOptions are set to Fill, are fully constrained which means that the invalidation cycle will be stopped at that child view. In order to have children of a Grid change layout dynamically they need to be a child of another View which is fully constrained. (As per the Grid sample).

Read more here:

https://michaelridland.com/xamarin/hacking-the-xamarin-forms-layout-system-for-fun-and-profit/

The StackLayout has no incidence, I change the code to have only a grid, same bug