User Identifier and Properties


Managing User Identifiers

User identifiers are used to uniquely identify different users.
Refer to the Managing User Identifiers document for an in-depth definition and understanding of why user identifiers are so important during experimentation.

Use SDK-managed identifiers

Flutter SDK includes features to automatically manage device identifiers. Therefore, the user can be automatically identified without having to manually pass the user identifier separately as a parameter.

Here's how to obtain the identifiers managed internally by the SDK:

import "package:hackle/hackle.dart";

// Get the internally managed device identifier
String deviceId = await HackleApp.getDeviceId();

// Get all the user information you've already set up
HackleUser user = await HackleApp.getUser();

Add a user identifier

You can set an identifier for the logged-in user. If you manage the device identifier yourself, you can set it separately.


import "package:hackle/hackle.dart";

// 1. Add logged in user identifier
await HackleApp.setUserId("LOGIN_ID");

// 2. Change device identifier
await HackleApp.setDeviceId("CUSTOM_DEVICE_ID");

Additional identifiers

Additional identifiers besides the default ones can be sent via the example code below.

import "package:hackle/hackle.dart";

HackleUser user = HackleUser.builder()
    .userId("LOGIN_ID") // User ID (can use Hackle integration identifier)
    .deviceId("CUSTOM_DEVICE_ID") // Device ID (can use Hackle integration identifier)
    .identifier("myCustomId", "CUSTOM_IDENTIFIER") // Custom ID

await HackleApp.setUser(user);


Hackle SDK supports adding properties to a User object.

  • Properties must be sent as a pair with both property name (key) and a property value (value).
  • The maximum number of properties that can be added to a User object is 64.

Property Key (Name)

  • The key should be set as a general name, but easily identifiable.
  • The character limit is 64 characters.
  • It is not case sensitive. For example, AGE and age are recognized as the same key.

Property Value

  • The value supports boolean, string, and number types.
  • In the case of string type, the character limit is 64 characters.
  • The string type is case-sensitive. For example, APPLE and apple are recognized as different property values.
  • In the case of number type, up to 15 integers and up to 6 decimal places are supported.


User objects are used as parameters in distributing traffic into test groups, determining feature flags, and sending user events.

Refer to the example code and add the desired properties to each user. In the example below, you can see that three properties (age, grade, is_paying_user) have been added.

import "package:hackle/hackle.dart";

await HackleApp.setUserProperty("age", 30);
await HackleApp.setUserProperty("grade", "GOLD");
await HackleApp.setUserProperty("is_paying_user", false);