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Chat SDKs Flutter v3
Chat SDKs Flutter
Chat SDKs
Version 3
Sendbird Chat SDK v3 for Flutter is no longer supported as a new version is released. Check out our latest Chat SDK v4


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In order to use the features of the Chat SDK in your client apps, a SendbirdSdk instance should be initiated in each client app through user authentication with the Sendbird server. The instance communicates and interacts with the server based on the authenticated user account and is allowed to use the Chat SDK's features. This page explains how to authenticate your user with the server.

Initialize the Chat SDK with Application ID

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To use our chat features, you must initialize a SendbirdSdk instance by passing your Sendbird application's Application ID as an argument to a parameter of the SendbirdSdk constructor method.

// Initialize the SendbirdSdk instance to use APIs in your app.
final sendbird = SendbirdSdk(appId: APP_ID);

Connect to the Sendbird server with a user ID

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By default, the Sendbird server authenticates a user with just a unique user ID. Then, the server queries the database to check for a match upon connection request. If no matching user ID is found, the server creates a new user account with a user ID. The user ID should be unique within a Sendbird application to be distinguishable from other identifiers such as a hashed email address or a phone number in your service.

While authenticating with just the user ID is convenient in the developing and testing stages of a service, a more secure authentication process using tokens is strongly recommended for most production environments.

Note: Go to the event handler page to learn more about the usages of the Chat SDK's handlers and callbacks.

// USER_ID below should be unique to your Sendbird application.
try {
    final user = await sendbird.connect(userId: USER_ID);
    // The user is connected to the Sendbird server.
} catch (e) {
    // Handle error.

Note: Apart from initializing the SendbirdSdk instance, you should connect to the Sendbird server before calling almost every method through the Chat SDK. If you attempt to call a method without connecting, ConnectionRequiredError is returned.

Connect to the Sendbird server with a user ID and a token

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For a more secure way of authenticating a user, you can require authentication with either an access token or a session token along with a user ID.

Using an access token

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Using Chat Platform API, you can create a user with their own access token or issue an access token for an existing user. Once an access token is issued, a user is required to provide the access token when logging in to the Sendbird application.

  1. Using the Chat Platform API, create a Sendbird user account with information submitted when a user signs up or logs in to your service.

  2. Save the user ID along with the issued access token to your securely managed persistent storage.

  3. When the user attempts to log in to the application, load the user ID and access token from the storage, and then pass them to the connect() method.

  4. Periodically replacing the user's access token is recommended to protect the account.

Note: From Settings > Application > Security > Access token permission setting on your dashboard, you're able to prevent users without an access token from logging in to your Sendbird application or restrict their access to read and write messages.

// USER_ID below should be unique to your Sendbird application.
try {
    final user = await sendbird.connect(userId: USER_ID, accessToken: AUTH_TOKEN);
    // The user is authenticated using the access token and is connected to the Sendbird server.
} catch (e) {
    // Handle error.

Using a session token

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You can also use a session token instead of an access token to authenticate a user. Session tokens are a more secure option because they expire after a certain period whereas access tokens don't. See Chat Platform API guides for further explanation about the difference between access token and session token, how to issue a session token, and how to revoke all session tokens.

Set a session handler

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When a user is authenticated with a session token, the Chat SDK connects the user to the Sendbird server and can send data requests to the server for ten minutes as long as the session token hasn't expired or hasn't been revoked.

Upon the user's session expiration, the Chat SDK will refresh the session internally using the SessionEventHandler class. However, if the session token has expired or has been revoked, the Chat SDK can't do so. In that case, the client app needs to implement a SessionEventHandler instance to refresh the token and pass it back to the SDK so that it can refresh the session again.

Note: A SessionEventHandler instance must be set before the server connection is requested.

The following code shows how to implement the handler methods.

class SessionEventHandler implements EventHandler {
  /// The client app needs to fetch a new token
  /// and pass on the newly retrieved token to SDK via success(NEW_TOKEN)
  /// or fail() if fetch has failed.
  /// In case the app decides not to refresh the session for this user,
  /// they should call success(null).
  void onSessionTokenRequired(Function(String) successCb, Function failCb) {}

  /// Informs when the SDK can't refresh the session.
  /// The client app should force a user to a login page to connect again.
  void onSessionClosed() {}

  /// Informs when the session key has expired.
  void onSessionExpired() {}

  /// Informs when the SDK has refreshed the session key.
  void onSessionRefreshed() {}

  /// Informs when the SDK runs into an error while refreshing the session key.
  void onSessionError(SBError error) {}

Because SessionEventHandler is a base class used to notify any event regarding the user's session and session token, you can register more events through SendbirdSdk.addSessionEventHandler. See an example in the following code below.

class MyHandler with SessionEventHandler {
  void onCloseSession() {
  // You can display a message to let the user know the session has been closed.

Disconnect from the Sendbird server

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A user can be disconnected from the Sendbird server when they no longer need to receive messages. However, the user will still receive push notifications for new messages from group channels they've joined.

When disconnected, all event handlers in a user's client app registered by the addChannelEventHandler() or addConnectionEventHandler() method stop receiving event callbacks from the server. Then, all internally cached data in the client app, such as the channels that are cached when the getChannel() method of OpenChannel or GroupChannel is called, are also flushed.

Note: By default, most of the data related to users, channels, and messages are internally cached in the SendbirdSdk instance of a user's client app, which are retrieved by the corresponding query instances or received through the event handlers.