Class SyncedStore

java.lang.Object
com.codename1.continuity.sync.SyncedStore
public final class SyncedStore extends Object

A small key/value store the platform carries between the devices one person signed in to, without them ever being in the same room.

This is the slow, patient half of continuity. com.codename1.continuity.Continuity hands the current activity to a device that is here, now; this keeps a handful of durable settings -- which theme, which sort order, which tutorial they already dismissed, the id of the document they are working through -- in step across everything they own.

SyncedStore.put("sortOrder", "byDate");
String order = SyncedStore.get("sortOrder", "byName");
What it is not

Not storage. Not a database, not a cache, and not a place for anything the app cannot cheerfully do without: the platform decides when to sync, the user can turn the whole mechanism off, and a device that has never been online has an empty store. Treat every read as "the value, or the default" -- which is why there is no read without a default.

Not secret. The contents leave the device and are held by the platform on the user's behalf. Credentials belong in com.codename1.security.SecureStorage.

Not large. The platform imposes a total size and a key count, both small; put reports a failure to write rather than pretending it stored something.

What it costs

Referencing this package is what makes an iOS build ask for the entitlement that gives the app a synced store, which in turn requires the capability to be enabled on the App ID. That is why it is a package of its own: an app that wants continuation to a nearby device and nothing else should not have to arrange an entitlement to get it. Where the platform has no such store -- Android, desktop, the browser -- isSupported() is false and every call here is an inert no-op, so the sensible shape is a synced value with a local default behind it.

  • Method Details

    • isSupported

      public static boolean isSupported()

      Whether this platform has a store that follows the user between devices.

      Returns

      true when the store is available

    • put

      public static boolean put(String key, String value)

      Writes a value, replacing any previous value for the key.

      Parameters
      • key: the key, must not be null or empty
      • value: the value, must not be null; use remove(String) to delete
      Returns

      true when the store holds the value afterwards; false when there is no store, or the platform would not take it -- a key count or a size past what it allows

    • get

      public static String get(String key, String def)

      Reads a value.

      There is no overload without a default on purpose: the store is genuinely empty on a device that has not synced yet, so every read has to have an answer for that.

      Parameters
      • key: the key, must not be null or empty
      • def: what to return when the key is absent or the store is unavailable
      Returns

      the value, or def

    • remove

      public static void remove(String key)

      Deletes a key. Deleting an absent key does nothing.

      Parameters
      • key: the key, must not be null or empty

    • keys

      public static String[] keys()

      Every key currently in the store, in no particular order.

      Returns

      the keys, never null and empty when the store is unavailable

    • addChangeListener

      public static void addChangeListener(SyncedStoreListener l)

      Registers a listener for changes made on the user's other devices.

      Parameters
      • l: the listener

    • removeChangeListener

      public static void removeChangeListener(SyncedStoreListener l)

      Removes a listener.

      Parameters
      • l: the listener

    • notifyChanged

      public static void notifyChanged()
      Internal. Invoked by the continuity framework when a port reports that the store changed underneath the app. Application code registers a SyncedStoreListener instead.