DevExpress XAF — Controllers & Actions

Controllers are the primary mechanism for adding custom features, UI interaction, and business logic to XAF applications. Actions are abstract UI elements (buttons, menus, dropdowns) that live inside controllers.

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Prerequisites & Installation

NuGet Packages

Controllers and Actions are part of the core XAF framework — no additional module registration is required.

Package	Purpose
DevExpress.ExpressApp	ViewController, WindowController, ObjectViewController<,>, Frame, View, ObjectSpace
DevExpress.ExpressApp.Actions	SimpleAction, SingleChoiceAction, PopupWindowShowAction, ParametrizedAction

Both packages are included in every XAF project by default.

Where to Place Controllers

Location	Scope
MySolution.Module\Controllers\	Platform-agnostic — runs in both Blazor and WinForms
MySolution.Blazor.Server\Controllers\	Blazor-only controllers
MySolution.Win\Controllers\	WinForms-only controllers

Controllers are discovered automatically — no manual registration in Module.cs is needed.

Using Statements

using DevExpress.ExpressApp;         // ViewController, ObjectViewController, WindowController
using DevExpress.ExpressApp.Actions; // SimpleAction, SingleChoiceAction, PopupWindowShowAction
using DevExpress.Persistent.Base;    // PredefinedCategory, ImageName

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Controller Types

Refer to references/controller-types.md

When you need to:

• Create a non-generic ViewController that activates for all views
• Create a ViewController<ListView> or ViewController<DetailView> scoped to a view type
• Create an ObjectViewController<ViewType, ObjectType> with typed access to the current object
• Create a WindowController for UI features not tied to specific views

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Controller Lifecycle

The lifecycle of a ViewController follows this order:

Constructor → OnFrameAssigned → OnActivated → OnViewControlsCreated → OnDeactivated

Event/Method	When	Use For
Constructor	Once, at application start	Create Actions, set Target* properties
OnFrameAssigned	Frame assigned to controller	Access Frame (View not yet available)
OnActivated	View set to Frame, controller matches criteria	Subscribe to events, access View/ObjectSpace
OnViewControlsCreated	Platform controls created for View	Access underlying UI controls (grid, editors)
OnViewChanged	View replaced in Frame	Re-evaluate activation criteria
OnDeactivated	View removed or Frame disposed	Unsubscribe from events, cleanup

Important: Always unsubscribe in OnDeactivated from events subscribed in OnActivated. XAF reuses controller instances within the same Frame.

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Controller Scope (Activation Conditions)

Refer to references/scope-and-state.md

When you need to:

• Set TargetObjectType, TargetViewType, TargetViewNesting, or TargetViewId in the constructor
• Dynamically control activation with Active["reason"] keys
• Combine generic type parameters with additional target constraints

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Action Types

Refer to references/action-types.md

When you need to:

• Create a SimpleAction button with click handling
• Create a SingleChoiceAction dropdown or radio-style selector
• Create a PopupWindowShowAction to display a popup view with object selection
• Create a ParametrizedAction text input or search box
• Add an [Action] attribute directly to a business class method for simple data operations

All actions inherit from ActionBase (DevExpress.ExpressApp.Actions).

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Action Scope & State

Refer to references/scope-and-state.md

When you need to:

• Hide or show an action dynamically with Active["reason"]
• Disable or enable an action with Enabled["reason"]
• Set action target properties (TargetObjectType, TargetObjectsCriteria, SelectionDependencyType)
• Choose a PredefinedCategory for action toolbar placement

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Accessing Built-in Controllers

Refer to references/common-patterns.md

When you need to:

• Use Frame.GetController<T>() to access built-in controllers (NewObjectViewController, DeleteObjectsViewController, etc.)
• Hide, disable, or customize built-in actions
• Subscribe to events on built-in controllers (e.g., ObjectCreated)

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Showing Views from Actions

Refer to references/views-and-popups.md

When you need to:

• Open a Detail View or List View from an action's Execute handler via ShowViewParameters
• Show a modal popup with OK/Cancel buttons via DialogController
• Add custom validation logic to the Accepting event of a popup dialog
• Choose a TargetWindow mode (current, new, modal)

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Dependency Injection & Common Patterns

Refer to references/common-patterns.md

When you need to:

• Use constructor injection or Application.ServiceProvider in controllers
• Customize the New Action's dropdown items
• Initialize new objects with default values via ObjectCreated event
• Access underlying UI controls in OnViewControlsCreated

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Troubleshooting

Symptom	Cause	Solution
Controller never activates	Target properties don't match	Check TargetObjectType, TargetViewType, TargetViewNesting
Action invisible	Active has a false entry	Check ActionBase.DiagnosticInfo or Active.GetKeys()
Action grayed out	Enabled has a false entry	Check Enabled.GetKeys() for the blocking reason
Duplicate actions	Inherited controller + parent both active	Inherit from the last descendant in the chain
Event handler fires multiple times	Not unsubscribing in OnDeactivated	Always unsubscribe in OnDeactivated
Controls not available in OnActivated	Controls created later	Use OnViewControlsCreated for UI control access

Constraints & Rules

1. No XAFML/Model Editor editing: All controller and action configuration via C# code.
2. Always unsubscribe from events in OnDeactivated.
3. Use ObjectViewController<V,T> when possible — avoids manual casting and scoping.
4. Do not call DoExecute directly unless in rare advanced scenarios (custom containers, keyboard shortcuts).
5. 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="")

• Controllers: devexpress_docs_get_content(url="https://docs.devexpress.com/content/eXpressAppFramework/112621/ui-construction/controllers-and-actions/controllers?md=true")

• Actions: devexpress_docs_get_content(url="https://docs.devexpress.com/content/eXpressAppFramework/112622/ui-construction/controllers-and-actions/actions?md=true")

• Controller scope: devexpress_docs_get_content(url="https://docs.devexpress.com/content/eXpressAppFramework/113103/ui-construction/controllers-and-actions/define-the-scope-of-controllers-and-actions?md=true")

• Built-in controllers: devexpress_docs_search(technologies=["eXpressAppFramework"], question="built-in controllers XAF")

• Action containers: devexpress_docs_get_content(url="https://docs.devexpress.com/content/eXpressAppFramework/112610/ui-construction/action-containers?md=true")

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