React Version 0.62.1
In your root project directory
Make sure you have already directory => android/app/src/main/assets/,
if not create directory, after that
create new file and save as index.android.bundle
and put your file like this android/app/src/main/assets/index.android.bundle
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// building bundles //
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npx react-native bundle --platform android --dev false --entry-file index.js --bundle-output android/app/src/main/assets/index.android.bundle --assets-dest android/app/src/main/res/
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// building Debug Apk //
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cd android && ./gradlew assembleDebug
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/////Get the Apk/////
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cd app/build/outputs/apk/
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// building Release Apk //
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cd android && ./gradlew assembleRelease