When a user logs into your app, you need to programmatically login the user into CometChat. But before you log in the user to CometChat, you need to create the user. Summing up- When a user registers in your app
  1. You add the user details in your database
  2. You create a user in CometChat
When a user logs into your app
  1. You log in the user to your app
  2. You log in the user to CometChat (programmatically)

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Creating a user

Ideally, user creation should take place at your backend. You can refer our Rest API to learn more about creating a user and use the appropriate code sample based on your backend language. However, if you wish to create users on the fly, you can use the createUser() method. This method takes a User object and the API Key as input parameters and returns the created User object if the request is successful. For more details on the fields present in the User class, please check this 
String apiKey = "AUTH_KEY"; // Replace with your API Key.
User user = new User();
user.setUid("user1"); // Replace with your uid for the user to be created.
user.setName("Kevin"); // Replace with the name of the user

CometChat.createUser(user, apiKey, new CometChat.CallbackListener<User>() {
@Override
public void onSuccess(User user) {
  Log.d("createUser", user.toString());
}

@Override
public void onError(CometChatException e) {
  Log.e("createUser", e.getMessage());
}
});
UID can be alphanumeric with underscore and hyphen. Spaces, punctuation and other special characters are not allowed.

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Updating a user

Updating a user similar to creating a user should ideally be achieved at your backend using the Restful APIs. For more information, you can check the update a user section. However, this can be achieved on the fly as well using the updateUser() method. This method takes a User object and the API Key as inputs and returns the updated User object on successful execution of the request. 
String apiKey = "AUTH_KEY"; // Replace with your API Key.
User user = new User();
user.setUid("user1"); // Replace with your uid for the user to be updated.
user.setName("Kevin Fernandez"); // Replace with the name of the user

CometChat.updateUser(user, apiKey, new CometChat.CallbackListener<User>() {
@Override
public void onSuccess(User user) {
  Log.d("updateUser", user.toString());
}

@Override
public void onError(CometChatException e) {
  Log.e("updateUser", e.getMessage());
}
});
Please make sure the User object provided to the updateUser() method has the UID of the user to be updated set.

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Updating logged-in user

Updating a logged-in user is similar to updating a user. The only difference being this method does not require an AuthKey. This method takes a User object as input and returns the updated User object on the successful execution of the request. 
User user = new User();
user.setName("Andrew Joseph");

CometChat.updateCurrentUserDetails(user, new CometChat.CallbackListener<User>() {
@Override
public void onSuccess(User user) {
  Log.d(TAG, user.toString());
}

@Override
public void onError(CometChatException e) {
  Log.d(TAG, e.getMessage());
}
});
By using the updateCurrentUserDetails() method one can only update the logged-in user irrespective of the UID passed. Also, it is not possible to update the role of a logged-in user.

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Deleting a user

Deleting a user can only be achieved via the Restful APIs. For more information please check the delete a usersection.

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User Class

FieldEditableInformation
uidspecified on user creation. Not editable after thatUnique identifier of the user
nameYesDisplay name of the user
avatarYesURL to profile picture of the user
linkYesURL to profile page
roleYesUser role of the user for role based access control
metadataYesAdditional information about the user as JSON
statusNoStatus of the user. Could be either online/offline
statusMessageYesAny custom status message that needs to be set for a user
lastActiveAtNoThe unix timestamp of the time the user was last active.
hasBlockedMeNoA boolean that determines if the user has blocked the logged in user
blockedByMeNoA boolean that determines if the logged in user has blocked the user
tagsYesA list of tags to identify specific users