Lazy Loading은 리소스가 필요할 때만 로드되는 디자인 패턴입니다. 이는 React Native 애플리케이션의 초기 로드 시간을 개선하고 메모리 소비를 줄이며 전반적인 성능을 향상시키는 데 도움이 됩니다.
지연 로딩 화면(코드 분할):
React Native에서 지연 로딩은 일반적으로 구성 요소에 사용되며, 특히 사용자가 자주 방문하지 않을 수 있는 다른 화면이 있는 경우에는 더욱 그렇습니다. 이러한 화면을 느리게 로드하면 초기 번들 크기가 줄어듭니다.
React.lazy() 및 Suspense를 사용한 지연 로딩:
React는 구성 요소의 지연 로딩을 활성화하기 위해 React.lazy() 함수를 도입했습니다. 지연 로딩을 사용하려면 구성 요소가 로드될 때까지 Suspense를 대체 수단으로 사용합니다.
일반적인 사용에서는 앱이 시작될 때 모든 리소스, 구성 요소, 라이브러리 및 데이터가 미리 로드됩니다. 이 접근 방식은 소규모 애플리케이션에는 적합하지만 앱이 성장함에 따라 비효율적이고 리소스 집약적이어서 성능과 로드 시간에 영향을 미칠 수 있습니다.
import React from 'react';
import HomeScreen from './screens/HomeScreen';
import ProfileScreen from './screens/ProfileScreen';
const App = () => {
return (
<>
<HomeScreen />
<ProfileScreen />
</>
);
};
export default App;
설명:
지연 로딩을 사용하면 필요할 때만 구성 요소, 라이브러리 또는 데이터가 로드됩니다. 필요한 리소스만 요청 시 로드되므로 초기 로드 시간과 메모리 사용량이 줄어들어 성능이 향상됩니다.
import React, { Suspense, lazy } from 'react';
import { ActivityIndicator } from 'react-native';
const HomeScreen = lazy(() => import('./screens/HomeScreen'));
const ProfileScreen = lazy(() => import('./screens/ProfileScreen'));
const App = () => {
return (
<Suspense fallback={<ActivityIndicator size="large" color="#0000ff" />}>
<HomeScreen />
<ProfileScreen />
</Suspense>
);
};
export default App;
설명:
| Feature | Normal Usage | Lazy Loading |
|---|---|---|
| Loading Strategy | Everything is loaded upfront when the app starts. | Components, resources, or data are loaded only when needed. |
| Initial Load Time | Higher, as all resources are loaded at once. | Lower, as only essential components are loaded upfront. |
| Memory Usage | Higher, as all components and resources are loaded into memory. | Lower, as only necessary components are loaded into memory. |
| User Experience | Slower startup but smoother transitions once loaded. | Faster startup but slight delay when loading resources. |
| Best for | Small applications with limited components. | Large applications where not all components are used initially. |
| Implementation | Simpler, as everything is bundled at once. | Requires managing dynamic imports and possibly loading states. |
Lazy loading ensures that screens or components are only mounted when they are accessed (when the user navigates to them), thus improving performance, especially in apps with multiple screens.
import React, { Suspense, lazy } from 'react';
import { createStackNavigator } from '@react-navigation/stack';
import { NavigationContainer } from '@react-navigation/native';
import { ActivityIndicator } from 'react-native';
// Lazy load screens
const HomeScreen = lazy(() => import('./screens/HomeScreen'));
const ProfileScreen = lazy(() => import('./screens/ProfileScreen'));
const Stack = createStackNavigator();
const App = () => {
return (
<NavigationContainer>
<Stack.Navigator>
<Stack.Screen
name="Home"
component={() => (
<Suspense fallback={<ActivityIndicator size="large" color="#0000ff" />}>
<HomeScreen />
</Suspense>
)}
/>
<Stack.Screen
name="Profile"
component={() => (
<Suspense fallback={<ActivityIndicator size="large" color="#0000ff" />}>
<ProfileScreen />
</Suspense>
)}
/>
</Stack.Navigator>
</NavigationContainer>
);
};
export default App;
Explanation:
In React Native, lazy loading can be achieved using libraries like react-native-fast-image or manually handling image loading by tracking visibility with tools like IntersectionObserver.
react-native-fast-image is a performant image component that provides built-in lazy loading.
npm install react-native-fast-image
import React from 'react';
import { View, ScrollView, Text } from 'react-native';
import FastImage from 'react-native-fast-image';
const LazyLoadingImages = () => {
return (
<ScrollView>
<Text>Scroll down to load images</Text>
<FastImage
style={{ width: 200, height: 200 }}
source={{
uri: 'https://example.com/my-image1.jpg',
priority: FastImage.priority.normal,
}}
resizeMode={FastImage.resizeMode.contain}
/>
<FastImage
style={{ width: 200, height: 200 }}
source={{
uri: 'https://example.com/my-image2.jpg',
priority: FastImage.priority.normal,
}}
resizeMode={FastImage.resizeMode.contain}
/>
</ScrollView>
);
};
export default LazyLoadingImages;
Explanation:
In cases where you don't want to use a third-party library, you can implement lazy loading by tracking when an image enters the viewport using tools like IntersectionObserver (web) or a custom scroll listener in React Native.
import React, { useState, useEffect } from 'react';
import { View, Image, ScrollView } from 'react-native';
const LazyImage = ({ src, style }) => {
const [isVisible, setIsVisible] = useState(false);
const onScroll = (event) => {
// Implement logic to determine if image is visible based on scroll position
const { y } = event.nativeEvent.contentOffset;
if (y > 100) { // Example: load image when scrolled past 100px
setIsVisible(true);
}
};
return (
<ScrollView onScroll={onScroll} scrollEventThrottle={16}>
<View>
{isVisible ? (
<Image source={{ uri: src }} style={style} />
) : (
<View style={style} />
)}
</View>
</ScrollView>
);
};
const App = () => {
return (
<LazyImage src="https://example.com/my-image.jpg" style={{ width: 200, height: 200 }} />
);
};
export default App;
Explanation:
When using Redux, you may want to lazy load certain reducers only when necessary, such as for specific screens or features.
Start by setting up a standard Redux store, but instead of adding all reducers upfront, create an injection method.
import { configureStore, combineReducers } from '@reduxjs/toolkit';
const staticReducers = {
// Add reducers that are needed from the start
};
export const createReducer = (asyncReducers = {}) => {
return combineReducers({
...staticReducers,
...asyncReducers,
});
};
const store = configureStore({
reducer: createReducer(),
});
// Store injected reducers here
store.asyncReducers = {};
export default store;
In the above code:
Create a helper function to inject new reducers dynamically into the store.
// Helper function to inject a new reducer dynamically
export function injectReducer(key, asyncReducer) {
if (!store.asyncReducers[key]) {
store.asyncReducers[key] = asyncReducer;
store.replaceReducer(createReducer(store.asyncReducers));
}
}
The injectReducer function checks if a reducer has already been added. If not, it injects it into the store and replaces the current root reducer.
Imagine you have a new page or feature that needs its own reducer. You can inject the reducer dynamically when this page is loaded.
import { lazy, Suspense, useEffect } from 'react';
import { useDispatch } from 'react-redux';
import { injectReducer } from './store';
import featureReducer from './features/featureSlice'; // The reducer for this feature
const FeatureComponent = lazy(() => import('./components/FeatureComponent'));
const FeaturePage = () => {
const dispatch = useDispatch();
useEffect(() => {
injectReducer('feature', featureReducer); // Dynamically load the reducer
}, [dispatch]);
return (
<Suspense fallback={<div>Loading...</div>}>
<FeatureComponent />
</Suspense>
);
};
export default FeaturePage;
Here:
The reducer for the feature is written as usual, using Redux Toolkit.
import { createSlice } from '@reduxjs/toolkit';
const featureSlice = createSlice({
name: 'feature',
initialState: { data: [] },
reducers: {
setData: (state, action) => {
state.data = action.payload;
},
},
});
export const { setData } = featureSlice.actions;
export default featureSlice.reducer;
You might want to remove a reducer when it's no longer needed, for example, when navigating away from a page.
Here’s how you can remove a reducer:
export function removeReducer(key) {
if (store.asyncReducers[key]) {
delete store.asyncReducers[key];
store.replaceReducer(createReducer(store.asyncReducers));
}
}
You can call this function when a feature or page is unmounted to remove its reducer from the store.
If you are using heavy third-party libraries, lazy loading them can help optimize performance.
import React, { useState } from 'react';
const HeavyComponent = React.lazy(() => import('heavy-library')); // React.lazy(() => import('moment'))
const App = () => {
const [showComponent, setShowComponent] = useState(false);
return (
<View>
<Button title="Load Heavy Component" onPress={() => setShowComponent(true)} />
{showComponent && (
<Suspense fallback={<Text>Loading...</Text>}>
<HeavyComponent />
</Suspense>
)}
</View>
);
};
Example: Lazy Loading Data:
import React, { useState, useEffect } from 'react';
import { FlatList, ActivityIndicator, Text } from 'react-native';
const LazyLoadData = () => {
const [data, setData] = useState([]);
const [loading, setLoading] = useState(true);
useEffect(() => {
fetch('https://api.example.com/data')
.then(response => response.json())
.then(json => {
setData(json);
setLoading(false);
});
}, []);
if (loading) {
return <ActivityIndicator />;
}
return (
<FlatList
data={data}
renderItem={({ item }) => <Text>{item.name}</Text>}
keyExtractor={item => item.id}
/>
);
};
export default LazyLoadData;
Explanation:
Lazy loading helps improve the performance, memory usage, and user experience of your React Native app, making it more efficient and responsive for users.
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