Dart (Flutter) SDK Reference

ConfigCat Dart (Flutter) SDK on GitHub

Getting Started

1. Add the ConfigCat SDK to your project

With Dart:

dart pub add configcat_client

With Flutter:

flutter pub add configcat_client

Or put the following directly to your pubspec.yml and run dart pub get or flutter pub get.

dependencies:
  configcat_client: ^2.0.2

2. Import the ConfigCat SDK

import 'package:configcat_client/configcat_client.dart';

3. Create the ConfigCat client with your SDK Key

final client = ConfigCatClient.get(sdkKey: '#YOUR-SDK-KEY#');

4. Get your setting value

final isMyAwesomeFeatureEnabled = await client.getValue(key: '<key-of-my-awesome-feature>', defaultValue: false);
if(isMyAwesomeFeatureEnabled) {
    doTheNewThing();
} else {
    doTheOldThing();
}

5. Close ConfigCat client​

You can safely shut down all clients at once or individually and release all associated resources on application exit.

ConfigCatClient.closeAll(); // closes all clients

client.close(); // closes the specific client

Configuring the ConfigCat Client

ConfigCat Client is responsible for:

• managing the communication between your application and ConfigCat servers.
• caching your setting values and feature flags.
• serving values quickly in a failsafe way.

ConfigCatClient.get(sdkKey: <sdkKey>) returns a client with default options.

Properties	Description
dataGovernance	Optional, defaults to global. Describes the location of your feature flag and setting data within the ConfigCat CDN. This parameter needs to be in sync with your Data Governance preferences. More about Data Governance. Available options: global, euOnly.
baseUrl	Optional, sets the CDN base url (forward proxy, dedicated subscription) from where the sdk will download the config.json.
connectTimeout	Optional, sets the underlying Dio HTTP client's connect timeout. More about the HTTP Client.
receiveTimeout	Optional, sets the underlying Dio HTTP client's receive timeout. More about the HTTP Client.
sendTimeout	Optional, sets the underlying Dio HTTP client's send timeout. More about the HTTP Client.
cache	Optional, sets a custom cache implementation for the client. More about cache.
mode	Optional, sets the polling mode for the client. More about polling modes.
logger	Optional, sets the internal logger and log level. More about logging.
override	Optional, sets local feature flag & setting overrides. More about feature flag overrides.
defaultUser	Optional, sets the default user. More about default user.
hooks	Optional, used to subscribe events that the SDK sends in specific scenarios. More about hooks.

final client = ConfigCatClient.get(
    sdkKey: '#YOUR-SDK-KEY#',
    options: ConfigCatOptions(
        mode: PollingMode.manualPoll(),
        logger: ConfigCatLogger(level: LogLevel.info)
    )
);

caution

We strongly recommend you to use the ConfigCatClient as a Singleton object in your application. The ConfigCatClient constructs singleton client instances for your SDK keys with its ConfigCatClient.get(sdkKey: <sdkKey>) static factory method. These clients can be closed all at once with the ConfigCatClient.closeAll() method or individually with client.close().

Anatomy of getValue()

Parameters	Description
key	REQUIRED. Setting-specific key. Set on ConfigCat Dashboard for each setting.
defaultValue	REQUIRED. This value will be returned in case of an error.
user	Optional, User Object. Essential when using Targeting. Read more about Targeting.

final value = await client.getValue(
    key: 'keyOfMySetting', 
    defaultValue: false,
    user: ConfigCatUser(identifier: '#USER-IDENTIFIER#'), // Optional User Object
);

Anatomy of getValueDetails()

getValueDetails() is similar to getValue() but instead of returning the evaluated value only, it gives more detailed information about the evaluation result.

Parameters	Description
key	REQUIRED. The key of a specific setting or feature flag. Set on ConfigCat Dashboard for each setting.
defaultValue	REQUIRED. This value will be returned in case of an error.
user	Optional, User Object. Essential when using Targeting. Read more about Targeting.

final details = await client.getValueDetails(
    key: 'keyOfMySetting', 
    defaultValue: false,
    user: ConfigCatUser(identifier: '#USER-IDENTIFIER#'), // Optional User Object
);

The details result contains the following information:

Field	Type	Description
value	Bool / String / Int / Double	The evaluated value of the feature flag or setting.
key	String	The key of the evaluated feature flag or setting.
isDefaultValue	Bool	True when the default value passed to getValueDetails() is returned due to an error.
error	String	In case of an error, this field contains the error message.
matchedEvaluationPercentageRule	PercentageRule	If the evaluation was based on a percentage rule, this field contains that specific rule.
matchedEvaluationRule	RolloutRule	If the evaluation was based on a targeting rule, this field contains that specific rule.
fetchTime	DateTime	The last download time of the current config.

User Object

The User Object is essential if you'd like to use ConfigCat's Targeting feature.

final user = ConfigCatUser(identifier: '435170f4-8a8b-4b67-a723-505ac7cdea92');   

final user = ConfigCatUser(identifier: '[email protected]');   

Customized user object creation:

Argument	Description
identifier	REQUIRED. Unique identifier of a user in your application. Can be any value, even an email address.
email	Optional parameter for easier targeting rule definitions.
country	Optional parameter for easier targeting rule definitions.
custom	Optional dictionary for custom attributes of a user for advanced targeting rule definitions. e.g. User role, Subscription type.

final user = ConfigCatUser(
    identifier: '435170f4-8a8b-4b67-a723-505ac7cdea92',
    email: '[email protected]',
    country: 'United Kingdom',
    custom: {
        'SubscriptionType': 'Pro', 
        'UserRole': 'Admin'
    }
);

Default user

There's an option to set a default user object that will be used at feature flag and setting evaluation. It can be useful when your application has a single user only, or rarely switches users.

You can set the default user object either on SDK initialization:

final client = ConfigCatClient.get(
    sdkKey: '#YOUR-SDK-KEY#',
    options: ConfigCatOptions(
        defaultUser: ConfigCatUser(identifier: '[email protected]')
    )
);

or with the setDefaultUser() method of the ConfigCat client.

client.setDefaultUser(ConfigCatUser(identifier: '[email protected]'));

Whenever the getValue(), getValueDetails(), getAllValues(), or getAllVariationIds() methods are called without an explicit user object parameter, the SDK will automatically use the default user as a user object.

final user = ConfigCatUser(identifier: '[email protected]');
client.setDefaultUser(user);

// The default user will be used at the evaluation process.
final value = await client.getValue(key: 'keyOfMySetting', defaultValue: false); 

When the user object parameter is specified on the requesting method, it takes precedence over the default user.

final user = ConfigCatUser(identifier: '[email protected]');
client.setDefaultUser(user);

final otherUser = ConfigCatUser(identifier: '[email protected]');

// otherUser will be used at the evaluation process.
final value = await client.getValue(key: 'keyOfMySetting', defaultValue: false, user: otherUser); 

For deleting the default user, you can do the following:

client.clearDefaultUser();

Polling Modes

The ConfigCat SDK supports 3 different polling mechanisms to acquire the setting values from ConfigCat. After latest setting values are downloaded, they are stored in the internal cache then all getValue() calls are served from there. With the following polling modes, you can customize the SDK to best fit to your application's lifecycle.
More about polling modes.

Auto polling (default)

The ConfigCat SDK downloads the latest values and stores them automatically every 60 seconds.

Use the the autoPollInterval option parameter of the PollingMode.autoPoll() to change the polling interval.

final client = ConfigCatClient.get(
    sdkKey: '<PLACE-YOUR-SDK-KEY-HERE>',
    options: ConfigCatOptions(
        mode: PollingMode.autoPoll(
            autoPollInterval: Duration(seconds: 100),
        ),
    )
);

Available options:

Option Parameter	Description	Default
autoPollInterval	Polling interval.	60
maxInitWaitTime	Maximum waiting time between the client initialization and the first config acquisition in seconds.	5

Lazy Loading

When calling getValue() the ConfigCat SDK downloads the latest setting values if they are not present or expired in the cache. In this case the getValue() will return the setting value after the cache is updated.

Use the cacheRefreshInterval option parameter of the PollingMode.lazyLoad() to set cache lifetime.

final client = ConfigCatClient.get(
    sdkKey: '<PLACE-YOUR-SDK-KEY-HERE>',
    options: ConfigCatOptions(
        mode: PollingMode.lazyLoad(
            // the cache will expire in 100 seconds
            cacheRefreshInterval: Duration(seconds: 100), 
        ),
    )
);

Available options:

Parameter	Description	Default
cacheRefreshInterval	Cache TTL.	60

Manual Polling

Manual polling gives you full control over when the config.json (with the setting values) is downloaded. ConfigCat SDK will not update them automatically. Calling forceRefresh() is your application's responsibility.

final client = ConfigCatClient.get(
    sdkKey: '<PLACE-YOUR-SDK-KEY-HERE>',
    options: ConfigCatOptions(
        mode: PollingMode.manualPoll(),
    )
);

client.forceRefresh();

getValue() returns defaultValue if the cache is empty. Call forceRefresh() to update the cache.

Hooks

With the following hooks you can subscribe to particular events fired by the SDK:

• onClientReady(): This event is sent when the SDK reaches the ready state. If the SDK is configured with lazy load or manual polling it's considered ready right after instantiation. If it's using auto polling, the ready state is reached when the SDK has a valid config.json loaded into memory either from cache or from HTTP. If the config couldn't be loaded neither from cache nor from HTTP the onClientReady event fires when the auto polling's maxInitWaitTime is reached.
• onConfigChanged(Map<string, Setting>): This event is sent when the SDK loads a valid config.json into memory from cache, and each subsequent time when the loaded config.json changes via HTTP.
• onFlagEvaluated(EvaluationDetails): This event is sent each time when the SDK evaluates a feature flag or setting. The event sends the same evaluation details that you would get from getValueDetails().
• error(String): This event is sent when an error occurs within the ConfigCat SDK.

You can subscribe to these events either on SDK initialization:

final client = ConfigCatClient.get(
    sdkKey: '#YOUR-SDK-KEY#',
    options: ConfigCatOptions(
        mode: PollingMode.manualPoll(),
        hooks: Hooks(
            onFlagEvaluated: (details) => /* handle the event */
        )
    )
);

or with the hooks property of the ConfigCat client:

client.hooks.addOnFlagEvaluated((details) => /* handle the event */);

Online / Offline mode

In cases when you'd want to prevent the SDK from making HTTP calls, you can put it in offline mode:

client.setOffline();

In offline mode, the SDK won't initiate HTTP requests and will work only from its cache.

To put the SDK back in online mode, you can do the following:

client.setOnline();

With client.isOffline() you can check whether the SDK is in offline mode or not.

Flag Overrides

With flag overrides you can overwrite the feature flags & settings downloaded from the ConfigCat CDN with local values. Moreover, you can specify how the overrides should apply over the downloaded values. The following 3 behaviours are supported:

• Local (OverrideBehaviour.localOnly): When evaluating values, the SDK will not use feature flags & settings from the ConfigCat CDN, but it will use all feature flags & settings that are loaded from local-override sources.

• Local over remote (OverrideBehaviour.localOverRemote): When evaluating values, the SDK will use all feature flags & settings that are downloaded from the ConfigCat CDN, plus all feature flags & settings that are loaded from local-override sources. If a feature flag or a setting is defined both in the downloaded and the local-override source then the local-override version will take precedence.

• Remote over local (OverrideBehaviour.remoteOverLocal): When evaluating values, the SDK will use all feature flags & settings that are downloaded from the ConfigCat CDN, plus all feature flags & settings that are loaded from local-override sources. If a feature flag or a setting is defined both in the downloaded and the local-override source then the downloaded version will take precedence.

You can set up the SDK to load your feature flag & setting overrides from a Map<String, Object>.

final client = ConfigCatClient.get(
    sdkKey: 'localhost',
    options: ConfigCatOptions(
        override: FlagOverrides(
            dataSource: OverrideDataSource.map({
                'enabledFeature': true, 
                'disabledFeature': false,
                'intSetting': 5,
                'doubleSetting': 3.14,
                'stringSetting': 'test',
            }),
            behaviour: OverrideBehaviour.localOnly
        )
    )
);

getAllKeys()

You can query the keys of each feature flag and setting with the getAllKeys() method.

final client = ConfigCatClient.get(sdkKey: '#YOUR-SDK-KEY#');
final keys = await client.getAllKeys();

getAllValues()

Evaluates and returns the values of all feature flags and settings. Passing a User Object is optional.

final client = ConfigCatClient.get(sdkKey: '#YOUR-SDK-KEY#');
final settingValues = await client.getAllValues();

// invoke with user object
final user = ConfigCatUser(identifier: '435170f4-8a8b-4b67-a723-505ac7cdea92');   
final settingValuesTargeting = await client.getAllValues(user);

Custom Cache

You have the option to inject your custom cache implementation into the client. All you have to do is to inherit from the ConfigCatCache abstract class:

class MyCustomCache extends ConfigCatCache {
    @override
    Future<String> read(String key) {
        // here you have to return with the cached value
    }

    @override
    Future<void> write(String key, String value) {
        // here you have to store the new value in the cache
    }
}

Then use your custom cache implementation:

final client = ConfigCatClient.get(
    sdkKey: '<PLACE-YOUR-SDK-KEY-HERE>',
    options: ConfigCatOptions(cache: MyCustomCache()));

HttpClient

The ConfigCat SDK internally uses a Dio HTTP client instance to download the latest config.json over HTTP. You have the option to customize the internal HTTP client.

HTTP Timeout

You can set the maximum wait time for a ConfigCat HTTP response by using Dio's timeouts.

final client = ConfigCatClient.get(
    sdkKey: '<PLACE-YOUR-SDK-KEY-HERE>',
    options: ConfigCatOptions(
        connectTimeout: Duration(seconds: 10), // timeout for establishing a HTTP connection with the server
        sendTimeout: Duration(seconds: 10), // timeout for sending a HTTP request to the server
        receiveTimeout: Duration(seconds: 10), // timeout for reading the server's HTTP response
    )
);

Default timeout values:

• connectTimeout: 10 seconds
• sendTimeout: 20 seconds
• receiveTimeout: 20 seconds

HTTP Proxy

If your application runs behind a proxy you can do the following:

import 'package:dio/adapter.dart';

(client.httpClient.httpClientAdapter as DefaultHttpClientAdapter)
    .onHttpClientCreate = (client) {
        client.findProxy = (uri) {
            return 'PROXY proxyHost:proxyPort';
        };
    };

Force refresh

Any time you want to refresh the cached config.json with the latest one, you can call the forceRefresh() method of the library, which initiates a new download and updates the local cache.

Logging

The default logger used by the SDK is the logger package, but you can override it with your implementation via the logger client option. The custom implementation must satisfy the Logger abstract class.

final client = ConfigCatClient.get(
    sdkKey: '<PLACE-YOUR-SDK-KEY-HERE>',
    options: ConfigCatOptions(
        logger: ConfigCatLogger(internalLogger: MyCustomLogger()), 
    )
);

You can customize the internally used logger instance.

import 'package:logger/logger.dart' as extlog;

final client = ConfigCatClient.get(
    sdkKey: '<PLACE-YOUR-SDK-KEY-HERE>',
    options: ConfigCatOptions(
        logger: ConfigCatLogger(
            internalLogger: DefaultLogger(internalLogger: extlog.Logger(/* customization of the logger package */))
        ), 
    )
);

You can change the verbosity of the logs by passing a LogLevel parameter to the logger option.

final client = ConfigCatClient.get(
    sdkKey: '<PLACE-YOUR-SDK-KEY-HERE>',
    options: ConfigCatOptions(
        logger: ConfigCatLogger(level: LogLevel.info), 
    )
);

Available log levels:

Level	Description
nothing	Turn the logging off.
error	Only error level events are logged.
warning	Default. Errors and Warnings are logged.
info	Errors, Warnings and feature flag evaluation is logged.
debug	All of the above plus debug info is logged. Debug logs can be different for other SDKs.

Info level logging helps to inspect how a feature flag was evaluated:

[I] TIME: 2022-01-20T18:22:02.313703 ConfigCat - Evaluating getValue(isPOCFeatureEnabled)
User object: {Identifier: 435170f4-8a8b-4b67-a723-505ac7cdea92, Email: [email protected]}
Evaluating rule: [Email:[email protected]] [CONTAINS] [@something.com] => no match
Evaluating rule: [Email:[email protected]] [CONTAINS] [@example.com] => match, returning: true

Sample Apps

Check out our Sample Applications how they use the ConfigCat SDK

• Console Application
• Flutter Application

Look Under the Hood

• ConfigCat Dart (Flutter) SDK's repository on GitHub
• ConfigCat Dart (Flutter) SDK's pub.dev page