Flutter

This is an optional library you can install if you're working with Flutter. It uses an internal queue to make calls fast and non-blocking. It also batches requests and flushes asynchronously, making it perfect to use in any part of your mobile app.

PostHog supports the iOS, macOS, Android and Web platforms.

Installation

PostHog is available for install via Pub.

Configuration

Set your PostHog API key and change the automatic event tracking on if you wish the library to take care of it for you.

Remember that the application lifecycle events won't have any special context set for you by the time it is initialized. If you are using a self-hosted instance of PostHog you will need to have the public hostname or IP for your instance as well.

To start, add posthog_flutter to your pubspec.yaml:

# rest of your code

dependencies:
  flutter:
    sdk: flutter
  posthog_flutter: ^4.0.1

# rest of your code

Then complete the set up for each platform:

For Session replay, you must setup the SDK manually by disabling the com.posthog.posthog.AUTO_INIT mode.

Android setup

There are 2 ways of initializing the SDK, automatically and manually.

Automatically:

Add your PostHog configuration to your AndroidManifest.xml file located in the android/app/src/main:

<manifest xmlns:android="http://schemas.android.com/apk/res/android" package="your.package.name">
    <application>
        <!-- ... other configuration ... -->
        <meta-data android:name="com.posthog.posthog.API_KEY" android:value="<ph_project_api_key>" />
        <meta-data android:name="com.posthog.posthog.POSTHOG_HOST" android:value="https://us.i.posthog.com" />  <!-- usually 'https://us.i.posthog.com' or 'https://eu.i.posthog.com' -->
        <meta-data android:name="com.posthog.posthog.TRACK_APPLICATION_LIFECYCLE_EVENTS" android:value="true" />
        <meta-data android:name="com.posthog.posthog.DEBUG" android:value="true" />
    </application>
</manifest>

Or manually (more control and more configurations available):

Add your PostHog configuration to your AndroidManifest.xml file located in the android/app/src/main:

<manifest xmlns:android="http://schemas.android.com/apk/res/android" package="your.package.name">
    <application>
        <!-- ... other configuration ... -->
        <meta-data android:name="com.posthog.posthog.AUTO_INIT" android:value="false" />
    </application>
</manifest>

And setup the SDK manually:

import 'package:flutter/material.dart';

import 'package:posthog_flutter/posthog_flutter.dart';

Future<void> main() async {
  // init WidgetsFlutterBinding if not yet
  WidgetsFlutterBinding.ensureInitialized();
  final config = PostHogConfig('YOUR_API_KEY_GOES_HERE');
  config.debug = true;
  config.captureApplicationLifecycleEvents = true;
  // or EU Host: 'https://eu.i.posthog.com'
  config.host = 'https://us.i.posthog.com';
  await Posthog().setup(config);
  runApp(MyApp());
}

In both cases, you'll also need to update the minimum Android SDK version to 21 in android/app/build.gradle:

// rest of your config

    defaultConfig {
        minSdkVersion 21
        // rest of your config
    }

// rest of your config

iOS setup

There are 2 ways of initializing the SDK, automatically and manually.

You'll need to have Cocoapods installed.

Automatically:

Add your PostHog configuration to the Info.plist file located in the ios/Runner directory:

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
<plist version="1.0">
<dict>
    <!-- rest of your configuration -->
    <key>com.posthog.posthog.API_KEY</key>
    <string><ph_project_api_key></string>
    <key>com.posthog.posthog.POSTHOG_HOST</key>
    <string>https://us.i.posthog.com</string>
    <key>com.posthog.posthog.CAPTURE_APPLICATION_LIFECYCLE_EVENTS</key>
    <true/>
    <key>com.posthog.posthog.DEBUG</key>
    <true/>
</dict>
</plist>

Or manually (more control and more configurations available):

Add your PostHog configuration to the Info.plist file located in the ios/Runner directory:

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
<plist version="1.0">
<dict>
    <!-- rest of your configuration -->
    <key>com.posthog.posthog.AUTO_INIT</key>
    <false/>
</dict>
</plist>

And setup the SDK manually:

import 'package:flutter/material.dart';

import 'package:posthog_flutter/posthog_flutter.dart';

Future<void> main() async {
  // init WidgetsFlutterBinding if not yet
  WidgetsFlutterBinding.ensureInitialized();
  final config = PostHogConfig('YOUR_API_KEY_GOES_HERE');
  config.debug = true;
  config.captureApplicationLifecycleEvents = true;
  // or EU Host: 'https://eu.i.posthog.com'
  config.host = 'https://us.i.posthog.com';
  await Posthog().setup(config);
  runApp(MyApp());
}

In both cases, you'll need to set the minimum platform version to iOS 13.0 in your Podfile:

platform :ios, '13.0'

# rest of your config

Web setup

For Web, add your Web snippet (which you can find in your project settings) in the <header> of your web/index.html file:

<!DOCTYPE html>
<html>

<head>
  <!-- ... other head elements ... -->

  <script async>
    !function(t,e){var o,n,p,r;e.__SV||(window.posthog=e,e._i=[],e.init=function(i,s,a){function g(t,e){var o=e.split(".");2==o.length&&(t=t[o[0]],e=o[1]),t[e]=function(){t.push([e].concat(Array.prototype.slice.call(arguments,0)))}}(p=t.createElement("script")).type="text/javascript",p.crossOrigin="anonymous",p.async=!0,p.src=s.api_host+"/static/array.js",(r=t.getElementsByTagName("script")[0]).parentNode.insertBefore(p,r);var u=e;for(void 0!==a?u=e[a]=[]:a="posthog",u.people=u.people||[],u.toString=function(t){var e="posthog";return"posthog"!==a&&(e+="."+a),t||(e+=" (stub)"),e},u.people.toString=function(){return u.toString(1)+".people (stub)"},o="capture identify alias people.set people.set_once set_config register register_once unregister opt_out_capturing has_opted_out_capturing opt_in_capturing reset isFeatureEnabled onFeatureFlags getFeatureFlag getFeatureFlagPayload reloadFeatureFlags group updateEarlyAccessFeatureEnrollment getEarlyAccessFeatures getActiveMatchingSurveys getSurveys getNextSurveyStep onSessionId".split(" "),n=0;n<o.length;n++)g(u,o[n]);e._i.push([i,s,a])},e.__SV=1)}(document,window.posthog||[]);
    posthog.init(
      '<ph_project_api_key>',
      {
        api_host:'https://us.i.posthog.com', // 'https://us.i.posthog.com' or 'https://eu.i.posthog.com'
      }
    )
  </script>
</head>

<!-- other elements -->

</html>

For more information please check: https://posthog.com/docs/libraries/js

Usage

Example

import 'package:flutter/material.dart';
import 'package:posthog_flutter/posthog_flutter.dart';

void main() => runApp(MyApp());

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      navigatorObservers: [
        // The PosthogObserver records screen views automatically
        PosthogObserver(),
      ],
      home: Scaffold(
        appBar: AppBar(
          title: Text('PostHog example app'),
        ),
        body: Center(
          child: FlatButton(
            child: Text('TRACK ACTION WITH PostHog'),
            onPressed: () async {
              await Posthog().capture(
                eventName: 'ButtonClicked',
                properties: {
                  'foo': 'bar',
                  'number': 1337,
                  'clicked': true,
                },
              );
            },
          ),
        ),
      )
    );
  }
}

Capturing events

You can send custom events using capture:

await Posthog().capture(
  eventName: 'user_signed_up',
);

Tip: We recommend using a [object] [verb] format for your event names, where [object] is the entity that the behavior relates to, and [verb] is the behavior itself. For example, project created, user signed up, or invite sent.

Setting event properties

Optionally, you can also include additional information in the event by setting the properties value:

await Posthog().capture(
  eventName: 'user_signed_up',
  properties: {
    'login_type': 'email',
    'is_free_trial': true
  }
);

Autocapture

PostHog autocapture automatically tracks the following events for you:

• Application Opened - when the app is opened from a closed state or when the app comes to the foreground (e.g. from the app switcher)
• Application Backgrounded - when the app is sent to the background by the user
• Application Installed - when the app is installed.
• Application Updated - when the app is updated.
• $screen - when the user navigates (if using navigatorObservers or go_router)

Identifying users

We highly recommend reading our section on Identifying users to better understand how to correctly use this method.

Using identify, you can associate events with specific users. This enables you to gain full insights as to how they're using your product across different sessions, devices, and platforms.

An identify call has the following arguments:

• userId: Required. A unique identifier for your user. Typically either their email or database ID.
• userProperties: Optional. A dictionary with key:value pairs to set the person properties
• userPropertiesSetOnce: Optional. Similar to userProperties. See the difference between userProperties and userPropertiesSetOnce

await Posthog().identify(
  userId: emailController.text, 
  userProperties: {"name": "Peter Griffin", "email": "peter@familyguy.com"},
  userPropertiesSetOnce: {"date_of_first_log_in": "2024-03-01"}
);

You should call identify as soon as you're able to. Typically, this is every time your app loads for the first time as well as directly after your user logs in. This ensures that events sent during your user's sessions are correctly associated with them.

When you call identify, all previously tracked anonymous events will be linked to the user.

Get the current user's distinct ID

You may find it helpful to get the current user's distinct ID. For example, to check whether you've already called identify for a user or not.

To do this, call PostHog().getDistinctId(). This returns either the ID automatically generated by PostHog or the ID that has been passed by a call to identify().

Alias

Sometimes, you want to assign multiple distinct IDs to a single user. This is helpful when your primary distinct ID is inaccessible. For example, if a distinct ID used on the frontend is not available in your backend.

In this case, you can use alias to assign another distinct ID to the same user.

await Posthog().alias(
  alias: 'distinct_id',
);

We strongly recommend reading our docs on alias to best understand how to correctly use this method.

Anonymous vs identfied events

PostHog captures two types of events: anonymous and identified

Identified events enable you to attribute events to specific users, and attach person properties. They're best suited for logged-in users.

Scenarios where you want to capture identified events are:

• Tracking logged-in users in B2B and B2C SaaS apps
• Doing user segmented product analysis
• Growth and marketing teams wanting to analyze the complete conversion lifecycle

Anonymous events are events without individually identifiable data. They're best suited for web analytics or apps where users aren't logged in.

Scenarios where you want to capture anonymous events are:

• Tracking a marketing website
• Content-focused sites
• B2C apps where users don't sign up or log in

Under the hood, the key difference between identified and anonymous events is that for identified events we create a person profile for the user, whereas for anonymous events we do not.

💡 Tip: Under our current pricing, anonymous events can be up to 4x cheaper than identified ones (due to the cost of processing them), so it's recommended you only capture identified events when needed.

How to capture anonymous events

PostHog captures anonymous events by default. However, this may change depending on your personProfiles config when initializing PostHog:

1. personProfiles: PostHogPersonProfiles.identifiedOnly (recommended) (default) - Anonymous events are captured by default. PostHog only captures identified events for users where person profiles have already been created.

2. personProfiles: PostHogPersonProfiles.always - Capture identified events for all events.

3. personProfiles: PostHogPersonProfiles.never - Capture anonymous events for all events.

For example:

final config = PostHogConfig(POSTHOG_API_KEY);
config.host = POSTHOG_HOST;
config.personProfiles = PostHogPersonProfiles.identifiedOnly;

How to capture identified events

If you've set the personProfiles config to IDENTIFIED_ONLY (the default option), anonymous events are captured by default. Then, to capture identified events, call any of the following functions:

• identify()
• alias()
• group()

When you call any of these functions, it creates a person profile for the user. Once this profile is created, all subsequent events for this user will be captured as identified events.

Alternatively, you can set personProfiles to ALWAYS to capture identified events by default.

Super Properties

Super Properties are properties associated with events that are set once and then sent with every capture call, be it a $screen, or anything else.

They are set using Posthog().register, which takes a key and value, and they persist across sessions.

For example, take a look at the following call:

import 'package:posthog_flutter/posthog_flutter.dart';

await Posthog().register("team_id", 22)

The call above ensures that every event sent by the user will include "team_id": 22. This way, if you filtered events by property using team_id = 22, it would display all events captured on that user after the Posthog().register call, since they all include the specified Super Property.

However, please note that this does not store properties against the User, only against their events. To store properties against the User object, you should use Posthog().identify. More information on this can be found on the Sending User Information section.

Removing stored Super Properties

Super Properties are persisted across sessions so you have to explicitly remove them if they are no longer relevant. In order to stop sending a Super Property with events, you can use Posthog().unregister, like so:

import 'package:posthog_flutter/posthog_flutter.dart';

await Posthog().unregister("team_id")

This will remove the Super Property and subsequent events will not include it.

If you are doing this as part of a user logging out you can instead simply use Posthog().reset which takes care of clearing all stored Super Properties and more.

Group analytics

Group analytics allows you to associate the events for that person's session with a group (e.g. teams, organizations, etc.). Read the Group Analytics guide for more information.

Note: This is a paid feature and is not available on the open-source or free cloud plan. Learn more here.

• Associate the events for this session with a group

await Posthog().group(groupType: "company", groupKey: "company_id_in_your_db");

• Associate the events for this session with a group AND update the properties of that group

await Posthog().group(
  groupType: "company", 
  groupKey: "company_id_in_your_db", 
  groupProperties: {
    "name": "ACME Corp"
});

The name is a special property which is used in the PostHog UI for the name of the Group. If you don't specify a name property, the group ID will be used instead.

Feature Flags

PostHog's feature flags enable you to safely deploy and roll back new features.

Boolean feature flags

if (await Posthog().isFeatureEnabled('flag-key')) {
  // Do something differently for this user

  // Optional: fetch the payload
  final matchedFlagPayload = await Posthog().getFeatureFlagPayload('flag-key');
}

Multivariate feature flags

if (await Posthog().getFeatureFlag('flag-key') == 'variant-key') { // replace 'variant-key' with the key of your variant
  // Do something differently for this user

  // Optional: fetch the payload
  final matchedFlagPayload = await Posthog().getFeatureFlagPayload('flag-key');
}

Ensuring flags are loaded before usage

Every time a user opens the app, we send a request in the background to fetch the feature flags that apply to that user. We store those flags in the storage.

This means that for most screens, the feature flags are available immediately – except for the first time a user visits.

Reloading feature flags

Feature flag values are cached. If something has changed with your user and you'd like to refetch their flag values, call:

await Posthog().reloadFeatureFlags();

Session replay

Note: Session replay is supported on the Flutter Web, Android and iOS environments.

To set up session replay web or mobile session replay in your project, all you need to do is install the Flutter SDK, enable "Record user sessions" in your project settings and enable the sessionReplay option.

If you're using the canvaskit renderer on Flutter Web, also enable the Canvas capture in your project settings.

Issues

Please file any issues, bugs, or feature requests in our GitHub repository.

Contributing

If you wish to contribute a change to this repo, please send a Pull Request.