---
name: robius-event-action
description: |
  CRITICAL: Use for Robius event and action patterns. Triggers on:
  custom action, MatchEvent, post_action, cx.widget_action,
  handle_actions, DefaultNone, widget action, event handling,
  事件处理, 自定义动作
risk: critical
source: community
date_added: "2026-09-04"
---
## Supporting material availability

This catalog copy contains the inline guidance below, but does not include the following supporting paths. They are external prerequisites, not bundled files:

- `<support-root>/references/action-patterns.md`
- `<support-root>/references/event-handling.md`
- `<support-root>/references/moly-action-patterns.md`

Ask for the original supporting material or an existing installation before using a step that depends on these paths; this catalog does not identify a verified download source for them. Resolve each path relative to that installation, inspect its contents, and verify any applicable license and execution prerequisites. Do not run a command or claim a referenced procedure was followed until its required file exists. Do not fabricate the missing scripts or treat an unrelated file with the same name as equivalent. Independent steps fully documented here can proceed within the user’s authorized scope; report any dependent step as unavailable.


# Robius Event and Action Patterns Skill

Best practices for event handling and action patterns in Makepad applications based on Robrix and Moly codebases.

**Source codebases:**
- **Robrix**: Matrix chat client - MessageAction, RoomsListAction, AppStateAction
- **Moly**: AI chat application - StoreAction, ChatAction, NavigationAction, Timer patterns

## When to Use
Use this skill when:
- Implementing custom actions in Makepad
- Handling events in widgets
- Centralizing action handling in App
- Widget-to-widget communication
- Keywords: makepad action, makepad event, widget action, handle_actions, cx.widget_action

## Custom Action Pattern

### Defining Domain-Specific Actions

```rust
use makepad_widgets::*;

/// Actions emitted by the Message widget
#[derive(Clone, DefaultNone, Debug)]
pub enum MessageAction {
    /// User wants to react to a message
    React { details: MessageDetails, reaction: String },
    /// User wants to reply to a message
    Reply(MessageDetails),
    /// User wants to edit a message
    Edit(MessageDetails),
    /// User wants to delete a message
    Delete(MessageDetails),
    /// User requested to open context menu
    OpenContextMenu { details: MessageDetails, abs_pos: DVec2 },
    /// Required default variant
    None,
}

/// Data associated with a message action
#[derive(Clone, Debug)]
pub struct MessageDetails {
    pub room_id: OwnedRoomId,
    pub event_id: OwnedEventId,
    pub content: String,
    pub sender_id: OwnedUserId,
}
```

### Emitting Actions from Widgets

```rust
impl Widget for Message {
    fn handle_event(&mut self, cx: &mut Cx, event: &Event, scope: &mut Scope) {
        self.view.handle_event(cx, event, scope);

        let area = self.view.area();
        match event.hits(cx, area) {
            Hit::FingerDown(_fe) => {
                cx.set_key_focus(area);
            }
            Hit::FingerUp(fe) => {
                if fe.is_over && fe.is_primary_hit() && fe.was_tap() {
                    // Emit widget action
                    cx.widget_action(
                        self.widget_uid(),
                        &scope.path,
                        MessageAction::Reply(self.get_details()),
                    );
                }
            }
            Hit::FingerLongPress(lpe) => {
                cx.widget_action(
                    self.widget_uid(),
                    &scope.path,
                    MessageAction::OpenContextMenu {
                        details: self.get_details(),
                        abs_pos: lpe.abs,
                    },
                );
            }
            _ => {}
        }
    }
}
```

## Centralized Action Handling in App

### Using MatchEvent Trait

```rust
impl MatchEvent for App {
    fn handle_startup(&mut self, cx: &mut Cx) {
        // Called once on app startup
        self.initialize(cx);
    }

    fn handle_actions(&mut self, cx: &mut Cx, actions: &Actions) {
        for action in actions {
            // Pattern 1: Direct downcast for non-widget actions
            if let Some(action) = action.downcast_ref::<LoginAction>() {
                match action {
                    LoginAction::LoginSuccess => {
                        self.app_state.logged_in = true;
                        self.update_ui_visibility(cx);
                    }
                    LoginAction::LoginFailure(error) => {
                        self.show_error(cx, error);
                    }
                }
                continue;  // Action handled
            }

            // Pattern 2: Widget action cast
            if let MessageAction::OpenContextMenu { details, abs_pos } =
                action.as_widget_action().cast()
            {
                self.show_context_menu(cx, details, abs_pos);
                continue;
            }

            // Pattern 3: Match on downcast_ref for enum variants
            match action.downcast_ref() {
                Some(AppStateAction::RoomFocused(room)) => {
                    self.app_state.selected_room = Some(room.clone());
                    continue;
                }
                Some(AppStateAction::NavigateToRoom { destination }) => {
                    self.navigate_to_room(cx, destination);
                    continue;
                }
                _ => {}
            }

            // Pattern 4: Modal actions
            match action.downcast_ref() {
                Some(ModalAction::Open { kind }) => {
                    self.ui.modal(ids!(my_modal)).open(cx);
                    continue;
                }
                Some(ModalAction::Close { was_internal }) => {
                    if *was_internal {
                        self.ui.modal(ids!(my_modal)).close(cx);
                    }
                    continue;
                }
                _ => {}
            }
        }
    }
}

impl AppMain for App {
    fn handle_event(&mut self, cx: &mut Cx, event: &Event) {
        // Forward to MatchEvent
        self.match_event(cx, event);

        // Pass events to widget tree
        let scope = &mut Scope::with_data(&mut self.app_state);
        self.ui.handle_event(cx, event, scope);
    }
}
```

## Action Types

### Widget Actions (UI Thread)

Emitted by widgets, handled in the same frame:

```rust
// Emitting
cx.widget_action(
    self.widget_uid(),
    &scope.path,
    MyAction::Something,
);

// Handling (two patterns)
// Pattern A: Direct cast for widget actions
if let MyAction::Something = action.as_widget_action().cast() {
    // handle...
}

// Pattern B: With widget UID matching
if let Some(uid) = action.as_widget_action().widget_uid() {
    if uid == my_expected_uid {
        if let MyAction::Something = action.as_widget_action().cast() {
            // handle...
        }
    }
}
```

### Posted Actions (From Async)

Posted from async tasks, received in next event cycle:

```rust
// In async task
Cx::post_action(DataFetchedAction { data });
SignalToUI::set_ui_signal();  // Wake UI thread

// Handling in App (NOT widget actions)
if let Some(action) = action.downcast_ref::<DataFetchedAction>() {
    self.process_data(&action.data);
}
```

### Global Actions

For app-wide state changes:

```rust
// Using cx.action() for global actions
cx.action(NavigationAction::GoBack);

// Handling
if let Some(NavigationAction::GoBack) = action.downcast_ref() {
    self.navigate_back(cx);
}
```

## Event Handling Patterns

### Hit Testing

```rust
impl Widget for MyWidget {
    fn handle_event(&mut self, cx: &mut Cx, event: &Event, scope: &mut Scope) {
        let area = self.view.area();
        match event.hits(cx, area) {
            Hit::FingerDown(fe) => {
                cx.set_key_focus(area);
                // Start drag, capture, etc.
            }
            Hit::FingerUp(fe) => {
                if fe.is_over && fe.is_primary_hit() {
                    if fe.was_tap() {
                        // Single tap
                    }
                    if fe.was_long_press() {
                        // Long press
                    }
                }
            }
            Hit::FingerMove(fe) => {
                // Drag handling
            }
            Hit::FingerHoverIn(_) => {
                self.animator_play(cx, id!(hover.on));
            }
            Hit::FingerHoverOut(_) => {
                self.animator_play(cx, id!(hover.off));
            }
            Hit::FingerScroll(se) => {
                // Scroll handling
            }
            _ => {}
        }
    }
}
```

### Keyboard Events

```rust
fn handle_event(&mut self, cx: &mut Cx, event: &Event, scope: &mut Scope) {
    if let Event::KeyDown(ke) = event {
        match ke.key_code {
            KeyCode::Return if !ke.modifiers.shift => {
                self.submit(cx);
            }
            KeyCode::Escape => {
                self.cancel(cx);
            }
            KeyCode::KeyC if ke.modifiers.control || ke.modifiers.logo => {
                self.copy_to_clipboard(cx);
            }
            _ => {}
        }
    }
}
```

### Signal Events

For handling async updates:

```rust
fn handle_event(&mut self, cx: &mut Cx, event: &Event, scope: &mut Scope) {
    if let Event::Signal = event {
        // Poll update queues
        while let Some(update) = PENDING_UPDATES.pop() {
            self.apply_update(cx, update);
        }
    }
}
```

## Action Chaining Pattern

Widget emits action → Parent catches and re-emits with more context:

```rust
// In child widget
cx.widget_action(
    self.widget_uid(),
    &scope.path,
    ItemAction::Selected(item_id),
);

// In parent widget's handle_event
if let ItemAction::Selected(item_id) = action.as_widget_action().cast() {
    // Add context and forward to App
    cx.widget_action(
        self.widget_uid(),
        &scope.path,
        ListAction::ItemSelected {
            list_id: self.list_id.clone(),
            item_id,
        },
    );
}
```

## Best Practices

1. **Use `DefaultNone` derive**: All action enums must have a `None` variant
2. **Use `continue` after handling**: Prevents unnecessary processing
3. **Downcast pattern for async actions**: Posted actions are not widget actions
4. **Widget action cast for UI actions**: Use `as_widget_action().cast()`
5. **Always call `SignalToUI::set_ui_signal()`**: After posting actions from async
6. **Centralize in App::handle_actions**: Keep action handling in one place
7. **Use descriptive action names**: `MessageAction::Reply` not `MessageAction::Action1`

## Reference Files

- `references/action-patterns.md` - Additional action patterns (Robrix)
- `references/event-handling.md` - Event handling reference (Robrix)
- `references/moly-action-patterns.md` - Moly-specific patterns
  - Store-based action forwarding
  - Timer-based retry pattern
  - Radio button navigation
  - External link handling
  - Platform-conditional actions (#[cfg])
  - UiRunner event handling

## Limitations
- Use this skill only when the task clearly matches the scope described above.
- Do not treat the output as a substitute for environment-specific validation, testing, or expert review.
- Stop and ask for clarification if required inputs, permissions, safety boundaries, or success criteria are missing.