Table of Contents

PrefabExtensionSetAttributePatch

PrefabExtensionSetAttributePatch is a specialized patch type in the v2 API used to add new XML attributes to an existing element or overwrite the values of existing ones in a Gauntlet Movie.

Unlike the legacy v1 attribute patch (which only allowed modifying a single attribute per class), the v2 patch allows you to modify or declare multiple attributes within a single patch class.

How It Works

A set-attribute patch targets an XML element selected by your XPath query. When applied:

  • Attribute already exists: Its value is overwritten with the new value you specified.
  • Attribute does not exist: A new attribute with the specified name and value is created and added to the element.

Key Rules and Considerations

  • Exact Case Matching: XML attributes in Gauntlet are strictly case-sensitive. Specifying isVisible will not overwrite an existing IsVisible attribute—it will create a duplicate attribute with different casing.
  • Target Node Must Be an Element: The XPath expression in [PrefabExtension] must select an XmlElement. If the XPath points to an attribute node (such as .../@Id) or a text node, the patch is ignored.
  • No Removal: PrefabExtensionSetAttributePatch cannot delete an attribute. If you need to remove an attribute entirely from a vanilla element, replace the node using PrefabExtensionInsertPatch with InsertType.Replace.
  • Runtime Evaluation: The Attributes property is evaluated each time the target movie is patched.

Implementation Details

To create an attribute patch:

  1. Inherit from PrefabExtensionSetAttributePatch.
  2. Decorate the class with [PrefabExtension("MovieName", "XPath")].
  3. Override the Attributes property, returning a List<Attribute>. Each item is an instance of the nested Attribute struct (new Attribute(string name, string value)).

Example: Modifying Multiple Attributes

The following example locates an OptionsTabToggle inside the "Options" movie, rebinds its visibility to a ViewModel property, and ensures it is enabled:

using Bannerlord.UIExtenderEx.Attributes;
using Bannerlord.UIExtenderEx.Prefabs2;
using System.Collections.Generic;

[PrefabExtension("Options", "descendant::OptionsScreenWidget[@Id='Options']/Children/OptionsTabToggle")]
internal sealed class ConfigureOptionsTabPatch : PrefabExtensionSetAttributePatch
{
    public override List<Attribute> Attributes => new()
    {
        new Attribute("IsVisible", "@IsDefaultCraftingMenuVisible"),
        new Attribute("IsEnabled", "true"),
        new Attribute("Brush", "Header.Tab.Toggle")
    };
}

XML Transformation

Before patch:

<Prefab>
    <Window>
        <OptionsScreenWidget Id="Options">
            <Children>
                <OptionsTabToggle IsVisible="true" />
            </Children>
        </OptionsScreenWidget>
    </Window>
</Prefab>

After patch:

<Prefab>
    <Window>
        <OptionsScreenWidget Id="Options">
            <Children>
                <OptionsTabToggle IsVisible="@IsDefaultCraftingMenuVisible" IsEnabled="true" Brush="Header.Tab.Toggle" />
            </Children>
        </OptionsScreenWidget>
    </Window>
</Prefab>

Linking Attributes to ViewModels

When an attribute value uses Gauntlet data-binding syntax (such as @PropertyName or *ParameterName):

  • The bound property must exist on the screen's active ViewModel or one of its registered ViewModel Mixins.
  • You can statically link the patch to the target ViewModel using [assembly: PrefabLink]. This enables the Roslyn Analyzers to validate attribute names and binding targets at compile time, warning you if a property is renamed or missing.

This page was last modified at 10/05/2026 13:34:58 +03:00 (UTC).

Commit Message
Author:    Vitalii Mikhailov
Commit:    f3b725a97c3f299c20e56b5f206e27142ec15edd

* Added C# Auto-Generated XML prefab compilation for patched and dynamic movies, matching vanilla UI performance

* Added name-based property binding fallback for ViewModel subtypes not declared on the parent
* Improved unparseable prefab error logging with name and file details
* Fixed game crash with 3-segment attribute paths
* Added Bannerlord.UIExtenderE...
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