Robius State Management

Robius State Management Skill

Selective Reading Rule

Start with:

• references/senior-master-standard.md
• references/usage-routing.md
• references/quality-checklist.md

Then load only the inherited docs, scripts, assets, or examples that match the user's actual task.

Best practices for state management and persistence in Makepad applications based on Robrix and Moly codebases.

Source codebases:

• Robrix: Matrix chat client - AppState, SelectedRoom, persistence via serde
• Moly: AI chat application - Central Store pattern, async initialization, Preferences

When to Use

Use this skill when:

• Designing application state structure
• Implementing state persistence
• Passing state through widget tree
• Managing UI state across sessions
• Keywords: app state, makepad state, persistence, Scope::with_data, save state, load state

Production Patterns

For production-ready state management patterns, see the _base/ directory:

AppState Structure

Core State Definition

use serde::{Serialize, Deserialize};
use std::collections::HashMap;
use matrix_sdk::ruma::OwnedRoomId;

/// App-wide state that is stored persistently across multiple app runs
/// and shared/updated across various parts of the app.
#[derive(Clone, Default, Debug, Serialize, Deserialize)]
pub struct AppState {
    /// The currently-selected room
    pub selected_room: Option<SelectedRoom>,

    /// Saved UI layout state for main view
    pub saved_layout_state: SavedLayoutState,

    /// Per-item saved states (e.g., per-space dock layouts)
    pub saved_state_per_item: HashMap<OwnedRoomId, SavedLayoutState>,

    /// Whether a user is currently logged in
    #[serde(skip)]  // Don't persist login state
    pub logged_in: bool,
}

/// Represents a currently selected item
#[derive(Clone, Debug, Serialize, Deserialize)]
pub enum SelectedRoom {
    JoinedRoom { room_name_id: RoomNameId },
    InvitedRoom { room_name_id: RoomNameId },
    Space { space_name_id: RoomNameId },
}

impl SelectedRoom {
    pub fn room_id(&self) -> &OwnedRoomId {
        match self {
            Self::JoinedRoom { room_name_id } => room_name_id.room_id(),
            Self::InvitedRoom { room_name_id } => room_name_id.room_id(),
            Self::Space { space_name_id } => space_name_id.room_id(),
        }
    }

    /// Upgrade from invited to joined state
    pub fn upgrade_invite_to_joined(&mut self, room_id: &RoomId) -> bool {
        match self {
            Self::InvitedRoom { room_name_id } if room_name_id.room_id() == room_id => {
                let name = room_name_id.clone();
                *self = Self::JoinedRoom { room_name_id: name };
                true
            }
            _ => false,
        }
    }
}

// Equality based on room_id only
impl PartialEq for SelectedRoom {
    fn eq(&self, other: &Self) -> bool {
        self.room_id() == other.room_id()
    }
}
impl Eq for SelectedRoom {}

Layout/Dock State Persistence

/// A snapshot of UI layout state for restoration
#[derive(Clone, Default, Debug, Serialize, Deserialize)]
pub struct SavedLayoutState {
    /// All items contained in the layout, keyed by ID
    pub layout_items: HashMap<LiveIdSerde, LayoutItemSerde>,

    /// Items currently open, keyed by ID
    pub open_items: HashMap<LiveIdSerde, SelectedRoom>,

    /// Order items were opened (chronological)
    pub item_order: Vec<SelectedRoom>,

    /// Currently selected item when state was saved
    pub selected_item: Option<SelectedRoom>,
}

/// Serializable wrapper for LiveId
#[derive(Clone, Debug, Hash, Eq, PartialEq, Serialize, Deserialize)]
pub struct LiveIdSerde(pub u64);

impl From<LiveId> for LiveIdSerde {
    fn from(id: LiveId) -> Self {
        Self(id.0)
    }
}

impl From<LiveIdSerde> for LiveId {
    fn from(s: LiveIdSerde) -> Self {
        LiveId(s.0)
    }
}

State Propagation via Scope

Passing State Through Widget Tree

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

        // Create Scope with AppState data
        let scope = &mut Scope::with_data(&mut self.app_state);

        // Pass to widget tree - all children can access AppState
        self.ui.handle_event(cx, event, scope);
    }
}

Accessing State in Child Widgets

impl Widget for RoomScreen {
    fn handle_event(&mut self, cx: &mut Cx, event: &Event, scope: &mut Scope) {
        // Access AppState from scope
        if let Some(app_state) = scope.data.get::<AppState>() {
            if let Some(selected) = &app_state.selected_room {
                self.update_for_room(cx, selected);
            }
        }

        self.view.handle_event(cx, event, scope);
    }
}

Modifying State

impl Widget for RoomsList {
    fn handle_event(&mut self, cx: &mut Cx, event: &Event, scope: &mut Scope) {
        // Mutable access to AppState
        if let Some(app_state) = scope.data.get_mut::<AppState>() {
            if self.selection_changed {
                app_state.selected_room = self.get_selected();
            }
        }
    }
}

Persistence Layer

File Paths

use std::path::{Path, PathBuf};

const LATEST_APP_STATE_FILE_NAME: &str = "latest_app_state.json";
const WINDOW_GEOM_STATE_FILE_NAME: &str = "window_geom_state.json";

/// Get user-specific persistent state directory
fn persistent_state_dir(user_id: &UserId) -> PathBuf {
    app_data_dir()
        .join("users")
        .join(user_id.to_string().replace(':', "_"))
}

/// Get app-wide data directory
fn app_data_dir() -> &'static Path {
    // Platform-specific app data location
    static APP_DATA_DIR: OnceLock<PathBuf> = OnceLock::new();
    APP_DATA_DIR.get_or_init(|| {
        dirs::data_dir()
            .unwrap_or_else(|| PathBuf::from("."))
            .join("myapp")
    })
}

Saving State

use std::io::Write;

pub fn save_app_state(
    app_state: AppState,
    user_id: OwnedUserId,
) -> anyhow::Result<()> {
    let file = std::fs::File::create(
        persistent_state_dir(&user_id).join(LATEST_APP_STATE_FILE_NAME)
    )?;
    let mut writer = std::io::BufWriter::new(file);
    serde_json::to_writer(&mut writer, &app_state)?;
    writer.flush()?;
    log!("Successfully saved app state to persistent storage.");
    Ok(())
}

/// Save window geometry state (user-agnostic)
pub fn save_window_state(window_ref: WindowRef, cx: &Cx) -> anyhow::Result<()> {
    let inner_size = window_ref.get_inner_size(cx);
    let position = window_ref.get_position(cx);
    let window_geom = WindowGeomState {
        inner_size: (inner_size.x, inner_size.y),
        position: (position.x, position.y),
        is_fullscreen: window_ref.is_fullscreen(cx),
    };
    std::fs::write(
        app_data_dir().join(WINDOW_GEOM_STATE_FILE_NAME),
        serde_json::to_string(&window_geom)?,
    )?;
    Ok(())
}

Loading State

/// Load app state with graceful fallback
pub async fn load_app_state(user_id: &UserId) -> anyhow::Result<AppState> {
    let state_path = persistent_state_dir(user_id).join(LATEST_APP_STATE_FILE_NAME);

    // Read file
    let file_bytes = match tokio::fs::read(&state_path).await {
        Ok(fb) => fb,
        Err(e) if e.kind() == std::io::ErrorKind::NotFound => {
            log!("No saved app state found, using default.");
            return Ok(AppState::default());
        }
        Err(e) => return Err(e.into()),
    };

    // Deserialize with fallback
    match serde_json::from_slice(&file_bytes) {
        Ok(app_state) => {
            log!("Successfully loaded app state.");
            Ok(app_state)
        }
        Err(e) => {
            error!("Failed to deserialize: {e}. May be incompatible format.");

            // Backup old file
            let backup_path = state_path.with_extension("json.bak");
            if let Err(backup_err) = tokio::fs::rename(&state_path, &backup_path).await {
                error!("Failed to backup old state: {}", backup_err);
            } else {
                log!("Old state backed up to: {:?}", backup_path);
            }

            log!("Using default app state.");
            Ok(AppState::default())
        }
    }
}

/// Load window geometry (synchronous, on UI thread)
pub fn load_window_state(window_ref: WindowRef, cx: &mut Cx) -> anyhow::Result<()> {
    let file = match std::fs::File::open(app_data_dir().join(WINDOW_GEOM_STATE_FILE_NAME)) {
        Ok(file) => file,
        Err(e) if e.kind() == std::io::ErrorKind::NotFound => return Ok(()),
        Err(e) => return Err(e.into()),
    };

    let window_geom: WindowGeomState = serde_json::from_reader(file)?;
    log!("Restoring window geometry: {window_geom:?}");

    window_ref.configure_window(
        cx,
        dvec2(window_geom.inner_size.0, window_geom.inner_size.1),
        dvec2(window_geom.position.0, window_geom.position.1),
        window_geom.is_fullscreen,
        "MyApp".to_string(),
    );
    Ok(())
}

Startup/Shutdown Integration

impl MatchEvent for App {
    fn handle_startup(&mut self, cx: &mut Cx) {
        // Load window geometry (sync, on UI thread)
        if let Err(e) = persistence::load_window_state(
            self.ui.window(ids!(main_window)), cx
        ) {
            error!("Failed to load window state: {}", e);
        }

        // Trigger async app state load
        let user_id = get_current_user_id();
        tokio::spawn(async move {
            match persistence::load_app_state(&user_id).await {
                Ok(app_state) => {
                    Cx::post_action(AppStateAction::RestoreFromPersistence(app_state));
                    SignalToUI::set_ui_signal();
                }
                Err(e) => error!("Failed to load app state: {}", e),
            }
        });
    }
}

impl AppMain for App {
    fn handle_event(&mut self, cx: &mut Cx, event: &Event) {
        if let Event::Shutdown = event {
            // Save window state (sync)
            if let Err(e) = persistence::save_window_state(
                self.ui.window(ids!(main_window)), cx
            ) {
                error!("Failed to save window state: {e}");
            }

            // Save app state (sync)
            if let Some(user_id) = current_user_id() {
                if let Err(e) = persistence::save_app_state(
                    self.app_state.clone(), user_id
                ) {
                    error!("Failed to save app state: {e}");
                }
            }
        }
        // ...
    }
}

Thread-Local State (UI-Only)

use std::{cell::RefCell, rc::Rc, collections::HashMap};

thread_local! {
    /// UI-thread-only cache
    static UI_CACHE: Rc<RefCell<HashMap<OwnedRoomId, CachedData>>> =
        Rc::new(RefCell::new(HashMap::new()));
}

/// Get cache reference (requires Cx to ensure UI thread)
pub fn get_ui_cache(_cx: &mut Cx) -> Rc<RefCell<HashMap<OwnedRoomId, CachedData>>> {
    UI_CACHE.with(Rc::clone)
}

/// Clear cache (requires Cx)
pub fn clear_ui_cache(_cx: &mut Cx) {
    UI_CACHE.with(|cache| cache.borrow_mut().clear());
}

Best Practices

1. Separate persistent vs runtime state: Use #[serde(skip)] for non-persistent fields
2. Use Scope::with_data() for tree propagation: Don't pass state through widget refs
3. Graceful deserialization fallback: Handle format changes between versions
4. Backup old state files: Preserve user data when format changes
5. User-specific persistent paths: Separate state per user account
6. Sync window state, async app state: Window geometry loads sync on UI thread
7. Thread-local for UI-only caches: Use thread_local! with Cx parameter guard

Reference Files

• references/persistence-patterns.md - Additional persistence patterns (Robrix)
• references/state-structures.md - State structure examples (Robrix)
• references/moly-state-patterns.md - Moly-specific patterns
  • Central Store struct containing all state
  • Async Store initialization with load_into_app()
  • App state check pattern (early return if not loaded)
  • Submodule state managers (Search, Downloads, Chats)
  • Provider syncing status tracking
  • Store action forwarding to submodules

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.