zello — Flutter plugin for the Zello Work Mobile SDKs

A Flutter plugin that wraps the native Zello Work Mobile SDKs (Android Kotlin, iOS Swift) and exposes a clean, idiomatic Dart API for:

  • Push-to-talk (works with the screen off / app in background)
  • Channel connect / disconnect with auto-reconnect events
  • Voice TX (start/stopTalking) and RX (incoming voice start/stop events)
  • Text messages
  • Presence / status
  • Hardware PTT buttons and Apple PushToTalk integration on iOS

There is no official Zello Flutter SDK — this package is a community platform-channel wrapper around the official native SDKs.

Installation

dependencies:
  zello: ^0.1.0

import 'package:zello/zello.dart';

Quick start

await Zello.instance.initialize(
  config: const ZelloConfig(appKey: '<your-zello-sdk-key>'),
);

final sub = Zello.instance.events.listen((event) {
  // event is a sealed ZelloEvent – switch on its subtypes
});

await Zello.instance.connect(
  network: 'mycompany.zellowork.com',
  token: jwtFromYourBackend, // RS256, short-lived
);

// PTT button pressed
await Zello.instance.startTalking('dispatch');
// PTT button released
await Zello.instance.stopTalking();

Public Dart API

Member Purpose
Zello.initialize({required ZelloConfig config}) One-time native init.
connect({required String network, required String token, String? username}) Connect to a Zello Work network with a short-lived JWT.
disconnect() Disconnect. Idempotent.
startTalking(String channel) Begin TX. Wire to PTT press.
stopTalking() End TX. Wire to PTT release.
sendTextMessage(String channel, String text) Send a text message.
setStatus(ZelloStatus status) Update presence.
getChannelState(String channel) → ZelloChannel Snapshot of a channel.
events Stream<ZelloEvent> (broadcast).
connectionState ValueListenable<ZelloConnectionState> for UI.
dispose() Tear down native resources.

All native failures surface as ZelloException(code, message, details). Events are a sealed Dart-3 hierarchy — switch exhaustively over ZelloConnectionStateChanged, ZelloIncomingVoiceStarted/Stopped, ZelloOutgoingTalkStateChanged, ZelloIncomingTextMessage, ZelloChannelStatusChanged, ZelloReconnectAttempt, ZelloErrorEvent, ZelloUnknownEvent.

Setup & Native SDK Installation

The Zello Mobile SDKs are gated behind a Zello Work subscription and cannot be redistributed via this repo. You must obtain them yourself and wire them in.

1. Obtain the SDK artifacts

  1. Sign in to your Zello Work admin portal.
  2. Provision an SDK key for your app.
  3. Download:
    • Android: AAR or Maven coordinates of the Zello Channels SDK.
    • iOS: XCFramework (or CocoaPods coordinate, if your subscription ships one).

2. Android wiring

In android/build.gradle.kts of this plugin (already scaffolded):

allprojects {
    repositories {
        google()
        mavenCentral()
        maven { url = uri("https://maven.zello.com/release") } // example
    }
}

dependencies {
    implementation("com.zello:zello-channel-sdk:<version>")
    // or, for a local AAR:
    // implementation(files("libs/zello-channel-sdk.aar"))
}

The plugin already declares (in android/src/main/AndroidManifest.xml):

  • RECORD_AUDIO
  • FOREGROUND_SERVICE, FOREGROUND_SERVICE_MICROPHONE
  • POST_NOTIFICATIONS (Android 13+)
  • BLUETOOTH_CONNECT (for headset PTT discovery)
  • MODIFY_AUDIO_SETTINGS, WAKE_LOCK, INTERNET, ACCESS_NETWORK_STATE
  • A foreground service ZelloForegroundService with android:foregroundServiceType="microphone" so PTT keeps working with the screen off.

You must request the runtime permissions in your host app (RECORD_AUDIO, POST_NOTIFICATIONS, BLUETOOTH_CONNECT) using permission_handler or your tool of choice before calling connect().

Then wire the real Zello SDK calls inside android/src/main/kotlin/com/zello/flutter/ZelloSdkAdapter.kt — every TODO in that file is a single SDK call (one line typically). The channel plumbing (ZelloPlugin.kt) does not need to change.

3. iOS wiring

In ios/zello.podspec (already scaffolded), uncomment one of:

# CocoaPods
s.dependency 'ZelloChannelKit', '~> 1.0'

# Or vendored XCFramework
# s.vendored_frameworks = 'Frameworks/ZelloSDK.xcframework'

In the host app's ios/Runner/Info.plist add:

<key>NSMicrophoneUsageDescription</key>
<string>Used for push-to-talk voice.</string>
<key>UIBackgroundModes</key>
<array>
  <string>audio</string>
  <string>push-to-talk</string>
</array>

In the host app's Runner.entitlements add:

<key>com.apple.developer.push-to-talk</key>
<true/>

…and enable the Push to Talk capability in Xcode (Signing & Capabilities). Without that entitlement, PT calls will fail silently — set enableApplePushToTalk: false in ZelloConfig if you cannot get the entitlement yet (background PTT will then be limited).

The plugin already configures AVAudioSession for playAndRecord / .voiceChat / .allowBluetooth / .defaultToSpeaker.

Wire the real Zello iOS SDK calls inside ios/Classes/ZelloSdkAdapter.swift — same pattern as Android, every TODO is one SDK call.

4. Backend token minting (auth)

The plugin only accepts a short-lived JWT (RS256) in connect(token:). It must never see the issuer private key.

Your backend should:

  1. Hold the Zello issuer + RS256 private key in a secret store.
  2. Mint a JWT per user / per session with a short expiry (e.g. 60–120 s).
  3. Return the JWT to the app over HTTPS.

The Flutter app simply receives the token and passes it to connect().

Threading & lifecycle

  • All MethodChannel.Result and EventSink calls are dispatched on the platform main thread (Handler(Looper.getMainLooper()) on Android, DispatchQueue.main on iOS).
  • The plugin holds a single native client per Flutter engine. dispose() cancels native listeners, tears down the session, and stops the Android foreground service.
  • Auto-reconnect attempts from the native SDK are surfaced as ZelloReconnectAttempt events — never swallowed.

Manual device-test checklist

The unit tests cover the Dart layer with a mocked MethodChannel. The native voice path must be exercised on real hardware:

  1. Connect on Android, lock the screen, press PTT (button or wired) — TX audio reaches the channel; foreground-service notification is visible.
  2. Receive a transmission while the app is backgrounded — RX audio plays through the speaker / Bluetooth headset.
  3. Kill network connectivity for 10 s, restore — ZelloReconnectAttempt then ZelloConnectionStateChanged(connected) arrive in Dart.
  4. iOS: with the PTT entitlement, background PTT keeps working and the system PTT UI appears in Control Center.
  5. iOS: route audio to a Bluetooth headset — AVAudioSession switches without dropping the session.
  6. Hardware PTT button on a Sonim/Crosscall device triggers start/stopTalking.
  7. Send/receive a text message; verify ZelloIncomingTextMessage.
  8. setStatus(ZelloStatus.busy) — other Zello clients see the new status.

Known limitations / TODO

  • All Zello SDK symbol references are placeholders behind ZelloSdkAdapter (Android + iOS). Replace the // TODO: confirm against Zello SDK vX blocks with the real SDK calls from your Zello Work portal. The channel layer does not need to change.
  • Image messages, location messages, and direct (1:1) voice are not yet exposed in the Dart API.
  • Channel user-list streaming is not yet exposed; only getChannelState(channel) snapshots.
  • Hardware PTT button auto-routing on Android relies on the Zello SDK's built-in handling; custom HID key mapping is not implemented here.
  • The iOS Apple-PushToTalk delegate (ApplePTTBridge) implements the minimum required methods; extend as you wire real Zello TX/RX.
  • No federated split (single-package). If/when this plugin gains macOS or web support, splitting into platform interface + implementations would be appropriate.
  • The example app's android/ and ios/ projects are not committed — run flutter create --platforms=android,ios . inside example/ once, then build.

Libraries

zello
Zello — Flutter plugin wrapping the native Zello Work Mobile SDKs.