Building a Persistent Dark Mode in HarmonyOS with ArkTS Preferences

Read the original article：Building a Persistent Dark Mode in HarmonyOS with ArkTS Preferences Problem Description Many HarmonyOS applications need to store small amounts of data locally —for example, user preferences, recently viewed items, or simple state flags. Developers often rely on in-memory variables, but those values disappear when the app restarts. We need a persistent and lightweight way to save and retrieve key–value pairs. Background Knowledge HarmonyOS provides the @kit.ArkData (new package name) module, which contains the preferences API for simple key–value storage. Data is stored as key–value pairs ( string , number , boolean , etc.) inside a preferences file on the device. You can access values using synchronous or asynchronous methods. flush() ensures that changes are physically written to disk. Troubleshooting Process Common pitfalls when working with preferences : Not calling or awaiting flush() after put() —changes may be lost if the app is killed before the buffer