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Overview

The AppSession class represents an active connection to a user’s glasses session. It provides methods to:
  • Subscribe to real-time events
  • Display content on glasses
  • Access hardware features
  • Manage settings

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Properties

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Core Properties

session.sessionId    // Unique session identifier
session.userId       // User's email address
session.capabilities // Hardware capabilities
session.isConnected  // Connection status

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Modules

session.events      // Event handlers
session.layouts     // Display layouts
session.camera      // Camera access
session.audio       // Audio playback
session.location    // Location services
session.dashboard   // Dashboard control
session.settings    // App settings

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Event Handling

All event handlers use the session.events object: 
// Subscribe to events
session.events.onTranscription((data) => {
  console.log(`User said: ${data.text}`);
});

session.events.onButtonPress((data) => {
  console.log(`Button ${data.buttonId} pressed`);
});

session.events.onHeadPosition((data) => {
  console.log(`Head position: ${data.position}`);
});

// Connection events
session.events.onDisconnected(() => {
  console.log('Session disconnected');
});

session.events.onReconnected(() => {
  console.log('Session reconnected');
});

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Display Control

Show content on the glasses display: 
// Simple text
await session.layouts.showTextWall('Hello World!');

// Reference card
await session.layouts.showReferenceCard({
  title: 'Weather',
  text: '72°F and sunny'
});

// Double text wall
await session.layouts.showDoubleTextWall(
  'Top section',
  'Bottom section'
);

// Clear display
await session.layouts.clearView();

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Capabilities

Check what hardware is available: 
if (session.capabilities.hasCamera) {
  // Camera is available
}

if (session.capabilities.hasMicrophone) {
  // Microphone is available
}

if (session.capabilities.hasDisplay) {
  // Display is available
}

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Connection Management

The SDK handles connection management automatically:
  • Auto-reconnect: Reconnects if connection drops
  • Grace period: Apps have 20 seconds to reconnect
  • State preservation: Session state survives reconnections
// Check connection status
if (session.isConnected) {
  // Safe to send data
}

// Manual disconnect
session.disconnect();

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Best Practices

if (session.capabilities.hasCamera) {
  const photo = await session.camera.requestPhoto();
} else {
  // Fallback for devices without camera
}

session.events.onDisconnected(() => {
  // Save state
  // Show offline message
});

session.events.onReconnected(() => {
  // Restore state
  // Resume normal operation
});

import { AppSession, TranscriptionData } from '@mentraos/sdk';

function handleTranscription(
  session: AppSession,
  data: TranscriptionData
) {
  // TypeScript provides intellisense and type checking
}

​
Common Patterns

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Voice Commands

session.events.onTranscription((data) => {
  const command = data.text.toLowerCase();
  
  if (command.includes('weather')) {
    showWeather(session);
  } else if (command.includes('time')) {
    showTime(session);
  }
});

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Button Navigation

let menuIndex = 0;
const menuItems = ['Home', 'Settings', 'About'];

session.events.onButtonPress((data) => {
  if (data.buttonId === 'main' && data.pressType === 'short') {
    menuIndex = (menuIndex + 1) % menuItems.length;
    session.layouts.showTextWall(menuItems[menuIndex]);
  }
});

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Continuous Updates

// Update display every 30 seconds
const interval = setInterval(async () => {
  if (session.isConnected) {
    const data = await fetchLatestData();
    await session.layouts.showReferenceCard({
      title: 'Live Data',
      text: data.value
    });
  }
}, 30000);

// Clean up on disconnect
session.events.onDisconnected(() => {
  clearInterval(interval);
});