UE UI: UMG, Slate, and Common UI

You are an expert in Unreal Engine's UI systems (UMG, Slate, and Common UI).

Context Check

Read .agents/ue-project-context.md to determine: which UI plugins are enabled (CommonUI, MVVM), target platforms (affects input method), whether this is multiplayer (widget ownership per player), and existing UI base class conventions.

Information Gathering

Before writing UI code, confirm: UI type (HUD, full-screen menu, modal, in-world WidgetComponent), input requirements (mouse, gamepad, keyboard), target platforms, and widget lifecycle (persistent, transient, or pooled).

1. UUserWidget in C++

// MyWidget.h
UCLASS()
class MYGAME_API UMyWidget : public UUserWidget
{
    GENERATED_BODY()
protected:
    virtual void NativeConstruct() override; // Bind delegates here — BindWidget refs valid
    virtual void NativeDestruct() override;
    virtual void NativeTick(const FGeometry& MyGeometry, float InDeltaTime) override;
};

// MyWidget.cpp
void UMyWidget::NativeConstruct()
{
    Super::NativeConstruct();
    if (PlayButton)
        PlayButton->OnClicked.AddDynamic(this, &UMyWidget::HandlePlayClicked);
}

Lifecycle and GC

// Creation — always pass the owning PlayerController for player-UI
UMyWidget* Widget = CreateWidget<UMyWidget>(GetOwningPlayer(), MyWidgetClass);
Widget->AddToViewport(0);          // ZOrder: higher = on top. Roots the widget (won't GC).
Widget->AddToPlayerScreen(0);      // Split-screen: ties to a specific player's viewport region
Widget->RemoveFromParent();        // Un-roots — may be GC'd if no UPROPERTY holds it.

UPROPERTY() TObjectPtr<UMyWidget> CachedWidget; // Strong ref keeps alive after RemoveFromParent

// Visibility
Widget->SetVisibility(ESlateVisibility::Collapsed); // Not drawn, takes no space
Widget->SetVisibility(ESlateVisibility::Hidden);    // Not drawn, takes space
Widget->SetVisibility(ESlateVisibility::Visible);   // Drawn, receives input
// HitTestInvisible: drawn, passes input through; SelfHitTestInvisible: children receive input

2. BindWidget Pattern

UCLASS()
class MYGAME_API UMyWidget : public UUserWidget
{
    GENERATED_BODY()
protected:
    UPROPERTY(meta=(BindWidget))             // Required — compiler warning if absent in UMG BP
    TObjectPtr<UButton> PlayButton;

    UPROPERTY(meta=(BindWidgetOptional))     // Optional — always null-check before use
    TObjectPtr<UTextBlock> SubtitleText;

    UPROPERTY(meta=(BindWidgetAnim), Transient) // Transient is required for anim bindings
    TObjectPtr<UWidgetAnimation> IntroAnim;

    UPROPERTY(meta=(BindWidget)) TObjectPtr<UTextBlock> ScoreText;
    UPROPERTY(meta=(BindWidget)) TObjectPtr<UImage> PlayerAvatar;
    UPROPERTY(meta=(BindWidget)) TObjectPtr<UProgressBar> HealthBar;
    UPROPERTY(meta=(BindWidget)) TObjectPtr<UListView> ItemList;
    UPROPERTY(meta=(BindWidget)) TObjectPtr<UScrollBox> ContentScroll; // Scrollable container
};

Name must match the UMG Blueprint widget name exactly (case-sensitive). Always null-check optional bindings.

3. Widget Interaction

UButton (Button.h)

// Delegates: OnClicked, OnPressed, OnReleased, OnHovered, OnUnhovered
PlayButton->OnClicked.AddDynamic(this, &UMyWidget::HandlePlayClicked);
PlayButton->OnHovered.AddDynamic(this, &UMyWidget::HandlePlayHovered);
PlayButton->SetColorAndOpacity(FLinearColor(1.f, 0.8f, 0.f, 1.f));
PlayButton->SetIsEnabled(false);
// UE5.2+: WidgetStyle, ColorAndOpacity, ClickMethod direct access deprecated — use setters

UTextBlock (TextBlock.h)

// SetText wipes any Blueprint binding on Text
ScoreText->SetText(FText::Format(NSLOCTEXT("HUD", "ScoreFmt", "Score: {0}"), FText::AsNumber(Score)));
ScoreText->SetColorAndOpacity(FSlateColor(FLinearColor::White));
ScoreText->SetTextTransformPolicy(ETextTransformPolicy::ToUpper);
ScoreText->SetTextOverflowPolicy(ETextOverflowPolicy::Ellipsis);

UImage (Image.h)

PlayerAvatar->SetBrushFromTexture(AvatarTexture, /*bMatchSize=*/false);
PlayerAvatar->SetBrushFromMaterial(IconMaterial);
UMaterialInstanceDynamic* MID = PlayerAvatar->GetDynamicMaterial();
MID->SetScalarParameterValue(TEXT("Opacity"), 0.5f);
PlayerAvatar->SetBrushFromSoftTexture(SoftTextureRef, false); // Async stream
PlayerAvatar->SetColorAndOpacity(FLinearColor(1.f, 1.f, 1.f, 0.5f));

UProgressBar (ProgressBar.h)

HealthBar->SetPercent(CurrentHealth / MaxHealth); // 0.0–1.0
HealthBar->SetFillColorAndOpacity(FLinearColor(0.f, 1.f, 0.f, 1.f));
LoadingBar->SetIsMarquee(true); // Indeterminate animation

UScrollBox (ScrollBox.h)

UScrollBox is a BindWidget-compatible container for scrollable content. Supports vertical and horizontal scroll. Add child widgets in Blueprint; query or modify scroll offset in C++:

ContentScroll->ScrollToEnd();
ContentScroll->SetScrollOffset(0.f);
ContentScroll->SetOrientation(Orient_Vertical); // default

UListView + UTileView + IUserObjectListEntry (ListView.h, TileView.h, IUserObjectListEntry.h)

UListView — virtualised vertical list. UTileView — same interface, displays items in a grid layout (set tile width/height in the widget Designer panel). Both use IUserObjectListEntry.

// Entry widget must implement the interface
UCLASS()
class UItemEntryWidget : public UUserWidget, public IUserObjectListEntry
{
    GENERATED_BODY()
    UPROPERTY(meta=(BindWidget)) TObjectPtr<UTextBlock> NameText;
protected:
    virtual void NativeOnListItemObjectSet(UObject* ListItemObject) override
    {
        IUserObjectListEntry::NativeOnListItemObjectSet(ListItemObject);
        if (UItemData* Data = Cast<UItemData>(ListItemObject))
            NameText->SetText(FText::FromString(Data->ItemName));
    }
};

// Populate
ItemList->ClearListItems();
for (const FItemInfo& Info : Items)
{
    UItemData* Data = NewObject<UItemData>(this);
    Data->ItemName = Info.Name;
    ItemList->AddItem(Data);
}
// Selection — NOTE: BP_OnItemClicked is Blueprint-only and private.
// For C++: override NativeOnItemClicked in a UListView subclass, or bind
// OnItemClickedInternal (protected delegate on UListViewBase).
UItemData* Selected = ItemList->GetSelectedItem<UItemData>();

4. Input Mode Management

// UI-only — full-screen menus. Game input blocked.
FInputModeUIOnly UIMode;
UIMode.SetWidgetToFocus(Widget->TakeWidget());
GetOwningPlayer()->SetInputMode(UIMode);
GetOwningPlayer()->SetShowMouseCursor(true);

// Game-only — restore gameplay.
GetOwningPlayer()->SetInputMode(FInputModeGameOnly());
GetOwningPlayer()->SetShowMouseCursor(false);

// Game and UI — HUD tooltips, keeps game input active.
FInputModeGameAndUI GameUIMode;
GameUIMode.SetLockMouseToViewportBehavior(EMouseLockMode::LockOnCapture);
GetOwningPlayer()->SetInputMode(GameUIMode);
GetOwningPlayer()->SetShowMouseCursor(true);

Set input mode from calling code (HUD/GameMode) after AddToViewport, not from NativeConstruct.

5. Common UI (Plugin)

See references/common-ui-setup.md for full plugin setup, GameViewportClient config, and layer architecture. Enable CommonUI and CommonInput plugins. Set viewport client to UCommonGameViewportClient in Project Settings > Maps & Modes > Game Viewport Client Class. UCommonGameViewportClient detects input method changes (gamepad vs mouse vs touch) and broadcasts them via UCommonInputSubsystem — this drives automatic gamepad/keyboard navigation and button prompt switching.

UCommonActivatableWidget (CommonActivatableWidget.h)

UCLASS()
class MYGAME_API UMyMenuScreen : public UCommonActivatableWidget
{
    GENERATED_BODY()
protected:
    virtual void NativeOnActivated() override;
    virtual void NativeOnDeactivated() override;
    virtual UWidget* NativeGetDesiredFocusTarget() const override { return CloseButton; }
    virtual TOptional<FUIInputConfig> GetDesiredInputConfig() const override
    {
        return FUIInputConfig(ECommonInputMode::Menu, EMouseCaptureMode::NoCapture);
    }
    UPROPERTY(meta=(BindWidget)) TObjectPtr<UCommonButtonBase> CloseButton;
};

void UMyMenuScreen::NativeOnActivated()
{
    Super::NativeOnActivated(); // Always call Super
    CloseButton->OnClicked().AddUObject(this, &UMyMenuScreen::DeactivateWidget);
}
void UMyMenuScreen::NativeOnDeactivated()
{
    CloseButton->OnClicked().RemoveAll(this);
    Super::NativeOnDeactivated(); // Always call Super
}

Widget Containers (CommonActivatableWidgetContainerBase.h)

UCommonActivatableWidgetContainerBase is the base class for Common UI widget containers. Two concrete subclasses:

• UCommonActivatableWidgetStack — shows only the topmost widget; deactivating reveals the previous one (stack behaviour). This is the correct stack class — do NOT use UCommonActivatableWidgetSwitcher here, which inherits from UCommonAnimatedSwitcher/UWidgetSwitcher and is a different widget entirely.
• UCommonActivatableWidgetQueue — FIFO queue; displays widgets sequentially, advancing to the next when the current deactivates.

UPROPERTY(meta=(BindWidget)) TObjectPtr<UCommonActivatableWidgetStack> MenuLayer;
UPROPERTY(meta=(BindWidget)) TObjectPtr<UCommonActivatableWidgetQueue> NotificationQueue;

// Push screen onto the stack — AddWidget creates the widget internally
UMyMenuScreen* Screen = Cast<UMyMenuScreen>(MenuLayer->AddWidget(UMyMenuScreen::StaticClass()));
Screen->ActivateWidget();

// Go back — deactivate re-activates the previous widget in the stack
Screen->DeactivateWidget();

// Queue a notification — plays after the current one finishes
NotificationQueue->AddWidget(UMyNotificationWidget::StaticClass());

UCommonButtonBase

Uses FCommonButtonEvent (declared via DECLARE_EVENT) — use AddUObject, not AddDynamic:

MyButton->OnClicked().AddUObject(this, &UMyScreen::HandleClick);
MyButton->OnClicked().RemoveAll(this); // In NativeOnDeactivated

UCommonUIActionRouter

Handles input routing between game and UI layers; Common UI drives it automatically via GetDesiredInputConfig. Access directly when you need to query the current input mode:

#include "Input/CommonUIActionRouterBase.h"
// Get() takes a const UWidget& — call from within a widget (or pass any valid UWidget in scope):
UCommonUIActionRouterBase* Router = UCommonUIActionRouterBase::Get(*ContextWidget); // ContextWidget: const UWidget&
if (Router) { /* query active input config */ }

Gamepad / Keyboard Navigation

Common UI provides automatic gamepad and keyboard navigation without extra setup. Key behaviours:

• UCommonButtonBase highlights automatically when it receives focus via D-pad or Tab navigation.
• UCommonActivatableWidget::NativeGetDesiredFocusTarget() controls which widget receives focus when the screen activates.
• When a widget deactivates, Common UI restores focus to the widget that was active before it opened — no manual focus bookkeeping required.
• Bind GetDesiredInputConfig to ECommonInputMode::Menu to suppress game input while a menu is open.

6. Slate Fundamentals

Use Slate for editor extensions, custom renderers, or when UMG doesn't expose required functionality.

SWidget is the abstract base of all Slate widgets. SCompoundWidget (shown below) is the typical subclass for custom widgets.

// Custom widget — SMyWidget.h
class SMyWidget : public SCompoundWidget
{
public:
    SLATE_BEGIN_ARGS(SMyWidget)
        : _LabelText(FText::GetEmpty()), _OnClicked() {}
        SLATE_ATTRIBUTE(FText, LabelText)
        SLATE_EVENT(FSimpleDelegate, OnClicked)
    SLATE_END_ARGS()

    void Construct(const FArguments& InArgs);
private:
    TAttribute<FText> LabelText;
    FSimpleDelegate OnClicked;
};

// SMyWidget.cpp
void SMyWidget::Construct(const FArguments& InArgs)
{
    LabelText = InArgs._LabelText;
    OnClicked = InArgs._OnClicked;
    ChildSlot
    [
        SNew(SButton)
        .OnClicked_Lambda([this]() -> FReply { OnClicked.ExecuteIfBound(); return FReply::Handled(); })
        [ SNew(STextBlock).Text(LabelText) ]
    ];
}

// Instantiation
TSharedRef<SMyWidget> W = SNew(SMyWidget).LabelText(NSLOCTEXT("UI", "Btn", "Go"));
TSharedPtr<SButton> Btn;
SAssignNew(Btn, SButton).OnClicked(FOnClicked::CreateUObject(this, &UMyClass::Handle));

Common Slate widgets: STextBlock, SButton, SVerticalBox, SHorizontalBox, SOverlay, SBorder, SBox, SScrollBox, SImage, SEditableTextBox.

Slate vs UMG: Use Slate for editor tools and maximum control. Use UMG for game runtime UI, Blueprint extensibility, animations, and BindWidget.

7. MVVM (UE 5.1+, ModelViewViewModel plugin)

// ViewModel — MyGameViewModel.h
UCLASS()
class MYGAME_API UMyGameViewModel : public UMVVMViewModelBase
{
    GENERATED_BODY()
public:
    // UE_MVVM_SET_PROPERTY_VALUE: checks equality, sets, broadcasts field change
    void SetScore(int32 NewScore) { UE_MVVM_SET_PROPERTY_VALUE(Score, NewScore); }
    void SetPlayerName(FText NewName) { UE_MVVM_SET_PROPERTY_VALUE(PlayerName, NewName); }
    int32 GetScore() const { return Score; }
    FText GetPlayerName() const { return PlayerName; }
private:
    UPROPERTY(BlueprintReadOnly, FieldNotify, Getter, meta=(AllowPrivateAccess))
    int32 Score = 0;
    UPROPERTY(BlueprintReadOnly, FieldNotify, Getter, meta=(AllowPrivateAccess))
    FText PlayerName;
};

// From game code — UI updates automatically via field notifications:
void AMyPlayerState::OnScoreChanged(int32 NewScore) { ViewModel->SetScore(NewScore); }

To bind a ViewModel at runtime: create with NewObject<UMyGameViewModel>(this), then configure in the widget Blueprint's Bindings panel. The UMVVMView component on the widget handles one-way and two-way property bindings automatically once the ViewModel class is set.

Common Mistakes

Build.cs

PublicDependencyModuleNames.AddRange(new string[] { "UMG", "Slate", "SlateCore" });
PrivateDependencyModuleNames.Add("CommonUI");      // If using CommonUI
PrivateDependencyModuleNames.Add("CommonInput");   // If using CommonInput
PrivateDependencyModuleNames.Add("ModelViewViewModel"); // If using MVVM

Related Skills

• ue-cpp-foundations — UPROPERTY meta specifiers, TObjectPtr, module setup
• ue-input-system — Enhanced Input, FInputModeXxx, input contexts
• ue-editor-tools — Slate for editor detail panels and custom tools