Storage in VWO FME Android SDK

The VWO FME Android SDK operates in a stateless mode by default, meaning each getFlag call triggers a fresh evaluation of the flag against the current user context.

To optimize performance and maintain consistency, the SDK provides both built-in storage and the ability to implement custom storage through a storage connector. This allows you to persist feature flag decisions in your preferred storage system.

Key Benefits of Storage

Improved Performance: Reduces network calls and latency by caching decisions locally
Consistent User Experience: Ensures users get the same experience across app sessions
Reduced Server Load: Minimizes the number of requests to VWO servers
Decision Stability: Once a decision is made for a user, it remains consistent even if campaign settings are modified in the VWO Application
Offline Functionality: Allows the SDK to function even when the device is offline

How to Implement a Storage Service

Built-in Storage

The SDK uses Android's SharedPreferences API for built-in storage, which provides a reliable, persistent key-value store that survives app restarts and updates.

Requirements for Built-in Storage

The context parameter is required for built-in storage to work properly
Storage is automatically enabled when a valid application context is provided

Example Usage with Built-in Storage

val options = VWOInitOptions()
options.sdkKey = "YOUR_SDK_KEY"
options.accountId = YOUR_ACCOUNT_ID
options.context = applicationContext // Required for built-in storage

VWO.init(options, object : IVwoInitCallback {
    override fun vwoInitSuccess(vwo: VWO, message: String?) {
        // VWO initialization succeeded
    }
    
    override fun vwoInitFailed(message: String?) {
        // VWO initialization failed
    }
})

VWOInitOptions options = new VWOInitOptions();
options.setSdkKey("YOUR_SDK_KEY");
options.setAccountId(YOUR_ACCOUNT_ID);
options.setContext(getApplicationContext()); // Required for built-in storage

VWO.init(options, new IVwoInitCallback() {
    @Override
    public void vwoInitSuccess(VWO vwo, String message) {
        // VWO initialization succeeded
    }
    
    @Override
    public void vwoInitFailed(String message) {
        // VWO initialization failed
    }
});

Custom Storage Implementation

You can implement your own storage mechanism by creating a class that extends the Connector class and implementing the required methods.

Storage Connector Interface

The storage connector should implement two main methods:

Method	Parameters	Description	Returns
`get`	`featureKey: String?`, `userId: String?`	Retrieves stored data for a specific feature and user	The stored data or null if not found
`set`	`data: Map<String, Any>`	Stores data for a specific feature and user	void

Example Custom Storage Implementation

class CustomStorageConnector : Connector() {
    /**
     * Retrieves data from storage
     * @param featureKey The feature key for the data
     * @param userId The user ID for the data
     * @return The stored data if found, or null otherwise
     */
    override fun get(featureKey: String?, userId: String?): Any? {
        // Implement your storage retrieval logic here
        // Return the stored data or null if not found
    }

    /**
     * Stores data in storage
     * @param data A map containing the data to be stored
     */
    override fun set(data: Map<String, Any>) {
        // Implement your storage logic here
        // Use data["featureKey"] and data["userId"] to store data
    }
}

// Usage
val options = VWOInitOptions()
options.sdkKey = "YOUR_SDK_KEY"
options.accountId = YOUR_ACCOUNT_ID
options.storage = CustomStorageConnector()

VWO.init(options, object : IVwoInitCallback {
    override fun vwoInitSuccess(vwo: VWO, message: String?) {
        // VWO initialization succeeded
    }
    
    override fun vwoInitFailed(message: String?) {
        // VWO initialization failed
    }
})

public class CustomStorageConnector extends Connector {
    /**
     * Retrieves data from storage
     * @param featureKey The feature key for the data
     * @param userId The user ID for the data
     * @return The stored data if found, or null otherwise
     */
    @Override
    public Object get(String featureKey, String userId) {
        // Implement your storage retrieval logic here
        // Return the stored data or null if not found
    }

    /**
     * Stores data in storage
     * @param data A map containing the data to be stored
     */
    @Override
    public void set(Map<String, Object> data) {
        // Implement your storage logic here
        // Use data.get("featureKey") and data.get("userId") to store data
    }
}

// Usage
VWOInitOptions options = new VWOInitOptions();
options.setSdkKey("YOUR_SDK_KEY");
options.setAccountId(YOUR_ACCOUNT_ID);
options.setStorage(new CustomStorageConnector());

VWO.init(options, new IVwoInitCallback() {
    @Override
    public void vwoInitSuccess(VWO vwo, String message) {
        // VWO initialization succeeded
    }
    
    @Override
    public void vwoInitFailed(String message) {
        // VWO initialization failed
    }
});

Important Notes

The context parameter is required for built-in storage to work properly
Custom storage implementations should handle data persistence and retrieval efficiently
Storage data persists between app launches
The SDK automatically manages storage operations for built-in storage
Custom storage implementations should be thread-safe
Consider implementing proper error handling in custom storage implementations
Storage operations should be fast to avoid impacting app performance