Breaking Changes in v5.0.0

This page lists all breaking changes between AvalonDock v4.x and v5.0.0, organized by category.

Package Structure

Serializers Extracted to Separate Packages

Impact: High — affects all projects using layout serialization.

The XML layout serializer has been moved from the core AvalonDock package to AvalonDock.Serializer.Xml. A new JSON serializer is available in AvalonDock.Serializer.Json.

Change	Details
Removed from	`Dirkster.AvalonDock`
Moved to	`Dirkster.AvalonDock.Serializer.Xml`
Old namespace	`AvalonDock.Layout.Serialization`
New namespace	`AvalonDock.Serializer.Xml`
Fix	Install the serializer package and update `using` statements.

- using AvalonDock.Layout.Serialization;
+ using AvalonDock.Serializer.Xml;

New Core Package

Impact: Low — automatically referenced.

A new AvalonDock.Core package contains UI-agnostic interfaces and models. It is automatically referenced by AvalonDock, so no explicit installation is needed.

Architecture

ILayoutEngine Introduction

Impact: Low to Medium — only affects custom layout logic.

The layout calculation logic has been formalized behind the ILayoutEngine interface.

Change	Details
Added	`ILayoutEngine` interface
Added	`DefaultLayoutEngine` implementation
Affected	Custom layout calculations using internal APIs
Fix	Implement `ILayoutEngine` for custom layout behavior.

Window Policy Members on Core Interfaces

Impact: Low — only affects custom implementations of the core interfaces.

IDockingManager and IRootDock each gained AllowFloatingWindows and AllowDetachedWindows. The shipped implementations (DockingManager, AvalonDock.Mvvm.RootDock) provide them; a hand-written implementation of either interface has to add them.

Change	Details
Added	`IDockingManager.AllowFloatingWindows`, `IDockingManager.AllowDetachedWindows`
Added	`IRootDock.AllowFloatingWindows`, `IRootDock.AllowDetachedWindows`
Fix	Add both `bool` properties, defaulting to `true` to keep the previous behavior.

Target Framework Changes

Dropped Frameworks

Impact: High — if targeting dropped frameworks.

Framework	Status
.NET Framework 4.0	❌ Removed
.NET Framework 4.5.2	❌ Removed
.NET Core 3.0 / 3.1	❌ Removed
.NET 5.0	❌ Removed
.NET 6.0 / 7.0 / 8.0	❌ Not targeted

Supported frameworks in v5.0.0:

.NET Framework 4.8
.NET 9.0 (with -windows TFM)
.NET 10.0 (with -windows TFM)

Fix: Update your project to target one of the supported frameworks:

<!-- .NET 9 -->
<TargetFramework>net9.0-windows</TargetFramework>

<!-- .NET 10 -->
<TargetFramework>net10.0-windows</TargetFramework>

<!-- .NET Framework 4.8 -->
<TargetFramework>net48</TargetFramework>

<!-- Multi-target -->
<TargetFrameworks>net10.0-windows;net9.0-windows;net48</TargetFrameworks>

New Features (Non-Breaking)

These additions are new in v5.0.0 and do not break existing code:

Feature	Package	Description
ToggleDockingManager	`AvalonDock`	VS Code / Rider-style sidebar with toggle buttons.
Standalone Windows	`AvalonDock`	`DetachAnchorableToWindow` moves a tool window into an ordinary top level window with its own taskbar entry (“Window” view mode). Survives layout serialization.
Window Policy	`AvalonDock`	`DockingManager.AllowFloatingWindows` and `AllowDetachedWindows` turn floating windows and the standalone “Window” view mode off for the whole manager. Also on `IRootDock` (MVVM) and `DockingOptions` (DI).
Toolbox Shortcuts	`AvalonDock`	`IToolbox.Shortcut` registers a key binding that toggles the toolbox and shows up in its tooltip.
Arc Theme	`AvalonDock.Themes.Arc`	Modern theme with dark/light variants.
VS Themes	`AvalonDock.Themes.VS`	`.vstheme` based Visual Studio themes with VS2015, VS2022 and VS2026 variants, plus loading of custom theme files.
JSON Serializer	`AvalonDock.Serializer.Json`	JSON-based layout serialization.
MVVM Base Classes	`AvalonDock.Mvvm`	`DockableBase`, `ToolboxBase`, `DockLayoutService`, etc.
MVVM CommunityToolkit	`AvalonDock.Mvvm.CommunityToolkit`	`ObservableDockableBase`, `ObservableToolboxBase` with source generators.
DI Integration	`AvalonDock.DependencyInjection`	`AddAvalonDock()` extension method.
Core Abstractions	`AvalonDock.Core`	`IFactory`, `IDockingManager`, `IAutoHideManager`, etc.
DTO Serialization	`AvalonDock.Core`	Serialization refactored to DTO layer; custom serializers can extend `LayoutSerializerBase`.

Behavioral Changes

Layout Restacking

A bug fix in v5.0.0 corrects the restacking behavior for bottom-docked panels. If your application relied on the previous (incorrect) behavior, you may notice panels appearing in different positions after restacking.

Fix: Test your layouts and adjust panel placement if needed.

Unresolved Items Are Dropped on Deserialization

Impact: Low — affects applications that read LayoutRoot.Hidden after restoring a layout.

When a stored layout contains an item whose content cannot be resolved — a tool window the application no longer offers, or one the LayoutSerializationCallback supplies no content for — that item is now removed from the layout entirely.

In v4 an unresolved anchorable was hidden instead: it stayed in LayoutRoot.Hidden with the pane and index it was stored at, and was written back into every layout saved afterwards. Unresolved documents were already removed, so anchorables were the exception rather than the rule. The v4 source described both cases as “skip this”.

Fix: Nothing to do in most applications. If yours attaches content after the layout was restored — a plugin that loads late, or a tool window created on first use that expects to find itself in the hidden list — request the old behavior explicitly:

var serializer = new XmlLayoutSerializer(dockManager)
{
    UnresolvedContentHandling = UnresolvedContentHandling.Hide
};

Prefer deciding per item where you can. Only the application can tell a tool window that will never come back from one whose plugin simply has not loaded yet, and parking only the latter keeps the stored layout free of entries nothing will ever claim:

serializer.LayoutSerializationCallback += (s, args) =>
{
    var content = FindContent(args.Model.ContentId);
    if (content != null)
    {
        args.Content = content;
        return;
    }

    // A plugin we know about but have not loaded yet: keep the entry so the tool window can
    // return to its stored position once the plugin supplies its content.
    if (_knownPluginContentIds.Contains(args.Model.ContentId))
        args.UnresolvedContentHandling = UnresolvedContentHandling.Hide;
};

Restoring a parked item once its content arrives:

var parked = dockManager.Layout.Hidden.FirstOrDefault(a => a.ContentId == contentId);
if (parked != null)
{
    parked.Content = pluginViewModel;
    parked.Show();
}

Show() puts the anchorable back into the pane and at the index it was stored at. If that pane is no longer part of the layout — a restored layout rebuilds the docked area from scratch — it docks to an existing tool window pane instead, creating one if the layout has none, so the call never silently does nothing. Under ToggleDockingManager use RestoreHiddenAnchorable, which places the tool window on the sidebar of its zone.

Note that args.Cancel = true always drops the item, under either setting.

Impact: Low — affects applications that set LayoutContent.ToolTip and never set it again.

A tool tip belongs to the content, not to the layout. LayoutItem pushes it down from the view every time the view is attached, and it is routinely a control or a binding, neither of which a layout file can describe. v4 wrote the text form of it into the file and read it back; v5 leaves it out.

Fix: Set the tool tip where you set the rest of the content — in the view, or on the view model the LayoutSerializationCallback supplies. A ToolTip attribute in a file written by v4 is ignored on read, so existing layout files still load.

Summary Table

Category	Change	Impact	Action
Packages	Serializers separated	High	Install serializer package
Namespaces	Serializer namespace moved	High	Update `using` statements
Architecture	`ILayoutEngine` added	Low	No action for default behavior
Architecture	Window policy members on `IDockingManager` / `IRootDock`	Low	Add both properties to custom implementations
Frameworks	.NET < 4.8 dropped	High	Upgrade target framework
Frameworks	.NET Core 3.x / 5 dropped	High	Upgrade target framework
Themes	Arc theme added	None	Optional adoption
Serialization	JSON serializer added	None	Optional adoption
Behavior	Bottom restack fix	Low	Test and verify layouts
Behavior	Unresolved layout items dropped	Low	Set `UnresolvedContentHandling.Hide` if you relied on `LayoutRoot.Hidden`
Behavior	`ToolTip` no longer stored in the layout	Low	Set it in the view or on the view model