fix: don't perform side-effects in setState

example/StackNavigator.tsx

@@ -7,6 +7,7 @@ import {
   NavigationState,
   NavigationProp,
   CommonAction,
+  InitialState,
 } from '../src/index';
 
 type Props = {
@@ -31,12 +32,11 @@ const StackRouter = {
   }: {
     routeNames: string[];
     initialRouteName?: string;
-  }): NavigationState {
+  }): InitialState {
     const index = routeNames.indexOf(initialRouteName);
 
     return {
       index,
-      names: routeNames,
       routes: routeNames.slice(0, index + 1).map(name => ({
         name,
         key: `${name}-${shortid()}`,

example/TabNavigator.tsx

@@ -7,6 +7,7 @@ import {
   NavigationState,
   NavigationProp,
   CommonAction,
+  InitialState,
 } from '../src/index';
 
 type Props = {
@@ -29,12 +30,11 @@ const TabRouter = {
   }: {
     routeNames: string[];
     initialRouteName?: string;
-  }): NavigationState {
+  }): InitialState {
     const index = routeNames.indexOf(initialRouteName);
 
     return {
       index,
-      names: routeNames,
       routes: routeNames.map(name => ({
         name,
         key: `${name}-${shortid()}`,

src/NavigationContainer.tsx

@@ -1,8 +1,8 @@
 import * as React from 'react';
-import { NavigationState } from './types';
+import { NavigationState, InitialState } from './types';
 
 type Props = {
-  initialState?: NavigationState;
+  initialState?: InitialState;
   children: React.ReactNode;
 };
 
@@ -10,10 +10,11 @@ const MISSING_CONTEXT_ERROR =
   "We couldn't find a navigation context. Have you wrapped your app with 'NavigationContainer'?";
 
 export const NavigationStateContext = React.createContext<{
-  state?: NavigationState;
-  setState: React.Dispatch<React.SetStateAction<NavigationState | undefined>>;
+  state?: NavigationState | InitialState;
+  getState: () => NavigationState | InitialState | undefined;
+  setState: (state: NavigationState) => void;
 }>({
-  get state(): any {
+  get getState(): any {
     throw new Error(MISSING_CONTEXT_ERROR);
   },
   get setState(): any {
@@ -22,10 +23,21 @@ export const NavigationStateContext = React.createContext<{
 });
 
 export default function NavigationContainer({ initialState, children }: Props) {
-  const [state, setState] = React.useState<NavigationState | undefined>(
-    initialState
-  );
-  const value = React.useMemo(() => ({ state, setState }), [state, setState]);
+  const [state, setState] = React.useState<
+    NavigationState | InitialState | undefined
+  >(initialState);
+
+  const stateRef = React.useRef(state);
+
+  React.useEffect(() => {
+    stateRef.current = state;
+  });
+
+  const getState = React.useCallback(() => stateRef.current, []);
+  const value = React.useMemo(() => ({ state, getState, setState }), [
+    getState,
+    state,
+  ]);
 
   return (
     <NavigationStateContext.Provider value={value}>

src/SceneView.tsx

@@ -8,12 +8,12 @@ type Props = {
   screen: ScreenProps;
   helpers: NavigationHelpers;
   route: Route & { state?: NavigationState };
-  initialState: NavigationState;
-  setState: React.Dispatch<React.SetStateAction<NavigationState | undefined>>;
+  getState: () => NavigationState;
+  setState: (state: NavigationState) => void;
 };
 
 export default function SceneView(props: Props) {
-  const { screen, route, helpers, initialState, setState } = props;
+  const { screen, route, helpers, getState, setState } = props;
 
   const navigation = React.useMemo(
     () => ({
@@ -23,26 +23,34 @@ export default function SceneView(props: Props) {
     [helpers, route]
   );
 
+  const stateRef = React.useRef(route.state);
+
+  React.useEffect(() => {
+    stateRef.current = route.state;
+  });
+
+  const getCurrentState = React.useCallback(() => stateRef.current, []);
+  const setCurrentState = React.useCallback(
+    (child: NavigationState | undefined) => {
+      const state = getState();
+
+      setState({
+        ...state,
+        routes: state.routes.map(r =>
+          r === route ? { ...route, state: child } : r
+        ),
+      });
+    },
+    [getState, route, setState]
+  );
+
   const value = React.useMemo(
     () => ({
       state: route.state,
-      setState<T = NavigationState | undefined>(child: T | ((state: T) => T)) {
-        setState((state: NavigationState = initialState) => ({
-          ...state,
-          routes: state.routes.map(r =>
-            r === route
-              ? {
-                  ...route,
-                  state:
-                    // @ts-ignore
-                    typeof child === 'function' ? child(route.state) : child,
-                }
-              : r
-          ),
-        }));
-      },
+      getState: getCurrentState,
+      setState: setCurrentState,
     }),
-    [initialState, route, setState]
+    [getCurrentState, route.state, setCurrentState]
   );
 
   return (

src/types.tsx

@@ -8,6 +8,11 @@ export type NavigationState = {
   routes: Array<Route & { state?: NavigationState }>;
 };
 
+export type InitialState = Omit<NavigationState, 'names'> & {
+  names?: undefined;
+  state?: InitialState;
+};
+
 export type Route = {
   name: string;
   key: string;
@@ -22,7 +27,7 @@ export type Router<Action extends NavigationAction = NavigationAction> = {
   initial(options: {
     routeNames: string[];
     initialRouteName?: string;
-  }): NavigationState;
+  }): InitialState;
   reduce(
     state: NavigationState,
     action: Action | CommonAction

src/useNavigationBuilder.tsx

@@ -8,7 +8,7 @@ import {
 } from './types';
 import Screen, { Props as ScreenProps } from './Screen';
 import SceneView from './SceneView';
-import * as BaseActions from './actions';
+import * as BaseActions from './BaseActions';
 
 type Options = {
   initialRouteName?: string;
@@ -38,40 +38,70 @@ export default function useNavigationBuilder(router: Router, options: Options) {
 
   const routeNames = Object.keys(screens);
   const initialState = React.useMemo(
-    () =>
-      router.initial({
-        routeNames: Object.keys(screens),
+    () => ({
+      ...router.initial({
+        routeNames,
         initialRouteName: options.initialRouteName,
       }),
+      names: routeNames,
+    }),
     // eslint-disable-next-line react-hooks/exhaustive-deps
     [options.initialRouteName, router, ...routeNames]
   );
 
-  const { state = initialState, setState } = React.useContext(
-    NavigationStateContext
-  );
+  const {
+    state: currentState = initialState,
+    getState: getCurrentState,
+    setState,
+  } = React.useContext(NavigationStateContext);
+
+  const getState = React.useCallback(() => {
+    let state = getCurrentState();
+
+    if (state === undefined) {
+      state = initialState;
+    }
+
+    if (state.names === undefined) {
+      state = { ...state, names: routeNames };
+    }
+
+    return state;
+    // eslint-disable-next-line react-hooks/exhaustive-deps
+  }, [getCurrentState, initialState, ...routeNames]);
 
   const parentNavigationHelpers = React.useContext(NavigationHelpersContext);
 
   const helpers = React.useMemo((): NavigationHelpers => {
-    const dispatch = (action: NavigationAction) =>
-      setState((s = initialState) => {
-        const result = router.reduce(s, action);
+    const dispatch = (action: NavigationAction) => {
+      const state = getState();
+      const result = router.reduce(state, action);
 
-        // If router returned `null`, let the parent navigator handle it
-        if (result === null && parentNavigationHelpers !== undefined) {
+      // If router returned `null`, let the parent navigator handle it
+      if (result === null) {
+        if (parentNavigationHelpers !== undefined) {
           parentNavigationHelpers.dispatch(action);
+        } else {
+          throw new Error(
+            `No navigators are able to handle the action "${action.type}".`
+          );
         }
+      } else {
+        setState(result);
+      }
+    };
 
-        return result;
-      });
-
-    const actions = { ...router.actions, ...BaseActions };
+    const actions = {
+      ...router.actions,
+      ...BaseActions,
+    };
 
+    // @ts-ignore
     return {
       ...parentNavigationHelpers,
       ...Object.keys(actions).reduce(
         (acc, name) => {
+          // @ts-ignore
           acc[name] = (...args: any) => dispatch(actions[name](...args));
           return acc;
         },
@@ -79,17 +109,17 @@ export default function useNavigationBuilder(router: Router, options: Options) {
       ),
       dispatch,
     };
-  }, [parentNavigationHelpers, router, setState, initialState]);
+  }, [router, parentNavigationHelpers, getState, setState]);
 
   const navigation = React.useMemo(
     () => ({
       ...helpers,
-      state,
+      state: currentState,
     }),
-    [helpers, state]
+    [helpers, currentState]
   );
 
-  const descriptors = state.routes.reduce(
+  const descriptors = currentState.routes.reduce(
     (acc, route) => {
       const screen = screens[route.name];
 
@@ -101,7 +131,7 @@ export default function useNavigationBuilder(router: Router, options: Options) {
                 helpers={helpers}
                 route={route}
                 screen={screen}
-                initialState={initialState}
+                getState={getState}
                 setState={setState}
               />
             </NavigationHelpersContext.Provider>