DevExpress XAF — Conditional Appearance

Dynamic UI styling and element visibility based on business object state.

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Prerequisites & Installation

NuGet Package

Install the platform-agnostic package (same for Blazor and WinForms — no platform-specific variants):

DevExpress.ExpressApp.ConditionalAppearance

Module Registration

Blazor — MySolution.Blazor.Server\Startup.cs:

using DevExpress.ExpressApp.ConditionalAppearance;

services.AddXaf(Configuration, builder => {
    builder.Modules
        .AddConditionalAppearance();
});

WinForms — MySolution.Win\Startup.cs:

using DevExpress.ExpressApp.ConditionalAppearance;

var builder = WinApplication.CreateBuilder();
builder.Modules
    .AddConditionalAppearance();

Using Statements for Business Classes

using DevExpress.ExpressApp.ConditionalAppearance; // AppearanceAttribute, enums
using DevExpress.ExpressApp.Editors;                // ViewItemVisibility enum

Supported Customization Matrix

	Font Color	Font Style	Back Color	Enabled	Visible
Cells in List View	✅	✅
Edited cells in List View				✅
Property Editors in Detail View	✅	✅	✅	✅	✅
Static Text in Detail View	✅	✅	✅		✅
Layout Items	✅	✅	✅		✅
Layout Groups / Tabbed Groups	✅	✅			✅
Actions				✅	✅

ORM Criteria Compatibility

Criteria strings in AppearanceAttribute use CriteriaOperator syntax, which is ORM-agnostic. Appearance rules themselves work identically with both XPO and EF Core. However:

• XPO-specific criteria functions (e.g., expressions relying on [PersistentAlias]-decorated properties) evaluate correctly in XPO but may not translate for EF Core.
• EF Core projects should verify complex criteria against the EF Core criteria translator if problems arise.
• XAF-level functions such as CurrentUserId() and LocalDateTimeToday() work with both ORMs.
• Avoid Delayed Properties and Free Joins in criteria — AppearanceController evaluates criteria during paint, which can cause UI flicker or corrupt control state in WinForms.

AppearanceAttribute — Declare Rules in Code

Apply [Appearance] to a business class or property. The attribute accepts the parameters below.

Parameter	Description	Example Values
Id	Unique rule identifier (positional, first argument)	"HighPrice"
AppearanceItemType	Target element type	"ViewItem", "Action", "LayoutItem"
TargetItems	Target item IDs (semicolon-separated)	"Name;Price", "*", "Delete"
Context	Where the rule applies	"ListView", "DetailView", "Any", specific View ID
Criteria	Criteria expression for activation	"Status = 'Active'"
Method	Boolean method name for activation	"IsHighPriority"
BackColor	Background color name	"Red", "LightYellow"
FontColor	Font color name	"Blue", "Gray"
FontStyle	Font style (DXFontStyle enum)	DXFontStyle.Bold, DXFontStyle.Italic
Enabled	Enable/disable state	false
Visibility	Show/hide	ViewItemVisibility.Hide
Priority	Order when multiple rules apply	1, 2

Id (Unique Rule Identifier)

The first positional argument. Must be unique within the class. The ID is used to identify the rule in AppearanceController events (e.g., AppearanceApplied, CustomApplyAppearance) so you can inspect or override specific rules by matching their ID in event handlers.

AppearanceItemType

Determines which category of UI elements the rule targets:

Value	Targets
ViewItem	Property Editors, Static Text items, List Editor cells
Action	Actions (toolbar buttons, menu items)
LayoutItem	Layout Items, Layout Groups, Tabbed Groups

Criteria

A CriteriaOperator-syntax string that determines when the rule activates. Supports logical operators:

[Appearance("UrgentOverdue", AppearanceItemType = "ViewItem", TargetItems = "*",
    Criteria = "Status = 'Overdue' AND Priority > 3",
    Context = "ListView", BackColor = "Red")]

When criteria cannot be expressed as a static string, use the Method parameter instead (see Method-Based Rule below).

TargetItems

Semicolon-delimited list of target element identifiers:

• TargetItems = "Name;Email;Phone" — targets the listed items
• TargetItems = "*" — targets all elements of the specified AppearanceItemType
• TargetItems = "*;ExcludedProp" — targets all elements except ExcludedProp (the wildcard followed by semicolon-separated names excludes those items)
• Omitted on a class-level attribute — typically requires explicit targeting; no items are affected by default
• Omitted on a property-level attribute ([Appearance] on a property) — the rule targets that specific property

For AppearanceItemType.Action, use the action's Id property (not its caption). For AppearanceItemType.LayoutItem, use the layout group's model identifier (not its display caption).

Discovering layout group IDs programmatically: Traverse the Application Model in code — e.g., cast View.Model to IModelDetailView and walk Layout.GetNodes<IModelLayoutGroup>(true) to inspect each group's Id. This avoids guessing IDs from display captions.

Visibility (ViewItemVisibility enum)

Value	Effect
ViewItemVisibility.Hide	Element removed from layout; surrounding elements collapse to fill the space
ViewItemVisibility.ShowEmptySpace	Element invisible but its space is preserved in the layout (acts as Hide in Blazor)
ViewItemVisibility.Show	Element visible (use to explicitly restore visibility)

Namespace: DevExpress.ExpressApp.Editors.

BackColor

A color name string (e.g., "Red", "LightYellow") or hex value compatible with System.Drawing.ColorConverter. Supported on: Property Editors in Detail View, Static Text, Layout Items. Not supported on read-only List View cells, Layout Groups, or Actions (see the matrix above).

FontStyle (DXFontStyle enum)

Available values: Bold, Italic, Strikeout, Underline. Combine with bitwise OR:

using DevExpress.Drawing;
// ...
FontStyle = DXFontStyle.Bold | DXFontStyle.Italic

When multiple FontStyle rules conflict, Regular has the lowest priority; other styles are combined by disjunction (both apply). The Priority parameter is ignored for FontStyle conflicts.

Priority (Conflict Resolution)

An integer that controls which rule wins when multiple rules affect the same element simultaneously:

• Higher value wins for BackColor and FontColor conflicts.
• Ignored for Enabled, Visibility, and FontStyle, which follow fixed precedence:
  • Enabled: false always beats true
  • Visibility: Hide > ShowEmptySpace > Show
  • FontStyle: Regular is lowest; other styles combined by disjunction
• When Priority values are equal, the winning rule is undefined — always set distinct priorities for conflicting rules.

// Priority = 2 wins over Priority = 1 for BackColor
[Appearance("CriticalRed", AppearanceItemType = "ViewItem", TargetItems = "*",
    Criteria = "Status = 'Critical'", BackColor = "Red", Priority = 2)]
[Appearance("WarningYellow", AppearanceItemType = "ViewItem", TargetItems = "*",
    Criteria = "DueDate < LocalDateTimeToday()", BackColor = "Yellow", Priority = 1)]
public class ProjectTask : BaseObject { /* ... */ }

Multiple Attributes on One Class

Stack multiple [Appearance] attributes on the same class. Each must have a unique Id. Rules are evaluated independently — multiple rules can apply simultaneously, and conflicting rules are resolved by Priority:

[Appearance("HighPrice", AppearanceItemType = "ViewItem", TargetItems = "*",
    Criteria = "Price > 100", Context = "ListView",
    BackColor = "Red", FontColor = "White", Priority = 2)]
[Appearance("MediumPrice", AppearanceItemType = "ViewItem", TargetItems = "*",
    Criteria = "Price > 50 AND Price <= 100", Context = "ListView",
    BackColor = "Yellow", FontColor = "Black", Priority = 1)]
[Appearance("InactiveStrikeout", AppearanceItemType = "ViewItem", TargetItems = "*",
    Criteria = "Status = 'Inactive'", Context = "ListView",
    FontStyle = DXFontStyle.Strikeout, FontColor = "Gray", Priority = 3)]
public class Product : BaseObject {
    public virtual string Name { get; set; }
    public virtual decimal Price { get; set; }
    public virtual ProductStatus Status { get; set; }
}

Hide Layout Group Pattern

Use AppearanceItemType.LayoutItem with Visibility = ViewItemVisibility.Hide and TargetItems matching the layout group's model identifier:

[Appearance("HideAddressGroup", AppearanceItemType = "LayoutItem",
    TargetItems = "Address",
    Criteria = "IsMarried = false", Context = "DetailView",
    Visibility = ViewItemVisibility.Hide)]
public class Contact : BaseObject {
    public virtual bool IsMarried { get; set; }
}

TargetItems must match the layout group's ID in the Application Model, not its display caption. Use ViewItemVisibility.Hide (not ShowEmptySpace) for groups — ShowEmptySpace leaves a blank gap.

Quick example — highlight an entire row:

using DevExpress.ExpressApp.ConditionalAppearance;

[Appearance("HighPrice", AppearanceItemType = "ViewItem", TargetItems = "*",
    Criteria = "Price > 50", Context = "ListView",
    BackColor = "Red", FontColor = "Maroon", Priority = 2)]
public class Product : BaseObject {
    public virtual decimal Price { get; set; }
}

Code Examples

Refer to references/code-examples.md

When you need to:

• Color a specific property in a ListView based on its value
• Disable a property editor in a DetailView conditionally
• Hide a layout group or tab based on object state
• Disable an Action when object state makes it invalid
• Use a method-based rule instead of a criteria string
• Stack multiple rules with Priority on one class

AppearanceController Events

Refer to references/controller-events.md

When you need to:

• Reset or override styling after a rule is applied (AppearanceApplied)
• Cancel or replace the default apply logic (CustomApplyAppearance)
• Add appearance rules dynamically at runtime (CollectAppearanceRules)
• Access applied appearance via IAppearanceFormat, IAppearanceEnabled, or IAppearanceVisibility

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Troubleshooting

Symptom	Cause	Solution
Appearance rule not applied	Module not added	Call AddConditionalAppearance()
Rule applies but no visual change	Unsupported combination (e.g., FontColor on an Action)	Check the supported customization matrix
Method-based rule not triggering	Method does not return bool or is not public	Ensure method is public bool MethodName()
Action not actually hidden in ListView	Using Visibility = Hide on Actions in a ListView — XAF keeps them visible but disabled	Prefer Enabled = false; hiding Actions in ListViews is silently converted to disabled
Need to change Action color/font	AppearanceAttribute only supports Enabled and Visibility for Actions — FontColor, BackColor, FontStyle are ignored	Use a platform-specific approach: access the action's underlying control in a controller (e.g., via CustomApplyAppearance or ActionBase.CustomizeControl event)

Criteria Safety

[Appearance] attribute literals are compile-time constants and are inherently safe. However, when constructing criteria strings at runtime (e.g., in a CollectAppearanceRules handler), never concatenate user-supplied input directly — this risks criteria injection.

Prefer CriteriaOperator.FromLambda<T> for compile-time safety. When FromLambda is not available (e.g., the AppearanceAttribute constructor requires a string), use CriteriaOperator.Parse with parameterised placeholders, then call .ToString():

using DevExpress.Data.Filtering;

// Preferred: FromLambda (compile-time safe)
string safeCriteria = CriteriaOperator.FromLambda<Product>(
    p => p.Category == userInput).ToString();

// Fallback: Parse with parameterised placeholder
string safeCriteria = CriteriaOperator.Parse("Category = ?", userInput).ToString();

This applies to any code that builds criteria from external values — CollectAppearanceRules dynamic rule construction, controller-based rule injection, or helper methods that compose criteria strings. Raw string concatenation (e.g., "Category = '" + userInput + "'") must never be used with user-supplied values.

Constraints & Rules

1. No XAFML/Model Editor file editing: Declare appearance rules via [Appearance] attribute in C# code.
2. Do not use Conditional Appearance for security: Use the Security System instead.
3. Prefer disabling Actions over hiding them: Hiding Actions in ListViews is not fully supported — XAF keeps them visible but disabled to avoid complex calculations and UI position shifts.
4. Version consistency: All DevExpress packages must use the same version.

Using DevExpress Documentation MCP

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• Search: devexpress_docs_search(technologies=["eXpressAppFramework"], question="")

• Fetch: devexpress_docs_get_content(url="")

• Conditional Appearance overview: devexpress_docs_get_content(url="https://docs.devexpress.com/content/eXpressAppFramework/113286/conditional-appearance?md=true")

• Appearance rules in code: devexpress_docs_get_content(url="https://docs.devexpress.com/eXpressAppFramework/113371/conditional-appearance/declare-conditional-appearance-rules-in-code?md=true")

• Customize appearance behavior: devexpress_docs_get_content(url="https://docs.devexpress.com/eXpressAppFramework/113374/conditional-appearance/how-to-customize-the-conditional-appearance-module-behavior?md=true")

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