Incorrect Page Layout and Context Menu Position with Avalonia 11.2.3 and WebView 3.120.8

[Jackhammer88]

Description:

When using Avalonia 11.2.3 with WebView 3.120.8, there are two layout-related issues:

Incorrect page layout on startup: The initial page rendering does not match the window size, resulting in a layout issue.
Context menu misplacement: When right-clicking inside the WebView without manually resizing the window first, the context menu often appears at incorrect coordinates.

Steps to Reproduce:

1. Create a basic Avalonia app with WebView (e.g., Avalonia 11.2.3 and WebView 3.120.8).
2. Set WebView to fill the window.

<Window xmlns="https://github.com/avaloniaui"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:vm="using:AvaloniaApplication2.ViewModels"
        xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
        xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
        xmlns:webview="clr-namespace:WebViewControl;assembly=WebViewControl.Avalonia"
        mc:Ignorable="d" d:DesignWidth="800" d:DesignHeight="450"
        x:Class="AvaloniaApplication2.Views.MainWindow"
        x:DataType="vm:MainWindowViewModel"
        Icon="/Assets/avalonia-logo.ico"
        Title="AvaloniaApplication2">

    <Design.DataContext>
        <vm:MainWindowViewModel/>
    </Design.DataContext>

    <webview:WebView x:Name="webview" Focusable="True" Address="{Binding Address}" />

</Window>

3. Set code of view model like this:

public partial class MainWindowViewModel : ViewModelBase
{
    public string Address { get; set; } = "http://your.web/site";
}

4. Run the application (without resizing the window).
5. Observe the page layout.
6. Right-click inside the WebView to open the context menu.

Expected Behavior:

The page should be rendered correctly to fit the window on startup.
The context menu should appear at the correct position under the cursor.

Actual Behavior:

The page layout is incorrectly sized on startup.
The context menu appears at the wrong coordinates if the window size has not been manually adjusted.

Environment:

Avalonia: 11.2.3
WebView: 3.120.8
OS: ALT Linux Starterkit 11 (Salvia)
.NET: 8

Additional Context:

It seems the WebView component is not recalculating its layout properly on the initial window creation. Manually resizing the window corrects both the page layout and context menu placement.

[SirePi]

Still happening on 3.120.10, Avalonia 11.3.9 on Windows 11, .net 10

A quick workaround is to have the webview start with IsVisible="False" in the xaml and have it become visible in OnLoaded

protected override void OnLoaded(RoutedEventArgs e)
{
    base.OnLoaded(e);
    webview.IsVisible = true;
}