---
title: "Set User Identifier"
slug: "mapp-engage-ios-sdk-set-user-identifier"
updated: 2026-05-07T08:57:31Z
published: 2026-05-07T08:57:31Z
canonical: "docs.mapp.com/mapp-engage-ios-sdk-set-user-identifier"
---

> ## Documentation Index
> Fetch the complete documentation index at: https://docs.mapp.com/llms.txt
> Use this file to discover all available pages before exploring further.

# Set User Identifier

## Overview

The Set User Identifier feature in iOS allows developers to assign a unique identifier (alias) to the device's user. This identifier helps maintain consistent user profiles, enables personalized communication, and supports user segmentation.

---

## Use Case

1. **Purpose**:
  - Link user-specific data, such as preferences or behaviours, across devices.
  - Enable targeted marketing campaigns and personalized notifications.
2. **Benefits**:
  - Improve user segmentation and targeting accuracy.
  - Provide a seamless and personalized user experience.

---

## Implementation Details

### Assign or Update a User Identifier

Use `setDeviceAlias:withCompletionHandler:` for the simple case, or `setDeviceAlias:withResendAttributes:withCompletionHandler:` when you need to control whether previously set custom attributes are re-sent to the backend together with the alias change.

**Swift**

```swift
// Set alias only
Appoxee.shared()?.setDeviceAlias("user12345") { error, data in
    if error == nil {
        print("User Identifier set successfully.")
    } else {
        print("Failed to set User Identifier: \(error?.localizedDescription ?? "Unknown error")")
    }
}

// Set alias and re-sync all previously set custom attributes
Appoxee.shared()?.setDeviceAlias("user12345", withResendAttributes: true) { error, data in
    if error == nil {
        print("User Identifier set successfully (attributes re-sent).")
    }
}

// Set alias without re-sending previously set custom attributes
Appoxee.shared()?.setDeviceAlias("user12345", withResendAttributes: false) { error, data in
    if error == nil {
        print("User Identifier set successfully (no attribute re-send).")
    }
}
```

**Objective-C**

```objectivec
// Set alias only
[[Appoxee shared] setDeviceAlias:@"user12345"
          withCompletionHandler:^(NSError * _Nullable error, id _Nullable data) {
    if (!error) {
        NSLog(@"User Identifier set successfully.");
    } else {
        NSLog(@"Failed to set User Identifier: %@", error.localizedDescription);
    }
}];

// Set alias and re-sync all previously set custom attributes
[[Appoxee shared] setDeviceAlias:@"user12345"
          withResendAttributes:YES
          withCompletionHandler:^(NSError * _Nullable error, id _Nullable data) {
    if (!error) {
        NSLog(@"User Identifier set successfully (attributes re-sent).");
    }
}];

// Set alias without re-sending previously set custom attributes
[[Appoxee shared] setDeviceAlias:@"user12345"
          withResendAttributes:NO
          withCompletionHandler:^(NSError * _Nullable error, id _Nullable data) {
    if (!error) {
        NSLog(@"User Identifier set successfully (no attribute re-send).");
    }
}];
```

**Parameter behaviour**

- `alias` — The unique identifier for the user.
- `withResendAttributes` — When `YES`/`true`, the SDK re-sends all previously set custom attributes for this device to ensure backend state is fully aligned (useful after data loss, migrations, or cross-device reconciliation). When `NO`/`false`, only the alias change is sent, avoiding additional network and processing overhead.
- `withCompletionHandler` — `AppoxeeCompletionHandler` block of type `^(NSError * _Nullable error, id _Nullable data)`. Inspect `error` to determine success; `data` is reserved for additional response payload and may be `nil`.

### Retrieve the User Identifier

Fetch the currently assigned alias. The returned `data` object is the alias string.

**Swift**

```swift
Appoxee.shared()?.getDeviceAlias { error, data in
    if error == nil, let alias = data as? String {
        print("Retrieved User Identifier: \(alias)")
    } else {
        print("Failed to retrieve User Identifier: \(error?.localizedDescription ?? "Unknown error")")
    }
}
```

**Objective-C**

```objectivec
[[Appoxee shared] getDeviceAliasWithCompletionHandler:^(NSError * _Nullable error, id _Nullable data) {
    if (!error) {
        NSString *alias = (NSString *)data;
        NSLog(@"Retrieved User Identifier: %@", alias);
    } else {
        NSLog(@"Failed to retrieve User Identifier: %@", error.localizedDescription);
    }
}];
```

### Remove the User Identifier

To disassociate the alias from the device, use `logoutWithOptin:`. The SDK clears the user-to-device association as part of the logout flow. The `optin` flag controls whether the device remains subscribed to push after the user is removed — see [Logout Device](/v1/docs/mapp-engage-ios-sdk-logout) for details and tenant-side considerations.

**Swift**

```swift
Appoxee.shared()?.logout(withOptin: true)
```

**Objective-C**

```objectivec
[[Appoxee shared] logoutWithOptin:YES];
```

> [!WARNING]
> Warning:
> 
> The legacy method `removeDeviceAliasWithCompletionHandler:` is deprecated in the public header. Use `logoutWithOptin:` instead.

---

## Best Practices

- **Use Unique Identifiers**: Ensure the identifier is unique for each user to avoid conflicts across devices.
- **Error Handling**: Inspect the `error` argument of every completion block to ensure reliable operation under varying network conditions.
- **Privacy Compliance**: Ensure that user identifiers comply with privacy regulations (e.g., GDPR) and are managed securely.

> [!NOTE]
> Keep in mind:
> 
> - User identifiers are device-specific but can be used to associate multiple devices with the same user profile.
> - Use meaningful identifiers like addresses, usernames, or system-generated IDs for clarity and management.
> - Test all identifier operations (set, retrieve, and remove) under different app states (foreground, background, and terminated) for reliability.