Events Guide

NOTE: This guide is a work in progress

Events Guide

Events are the heartbeat of communication in Wails applications. They allow different parts of your application to talk to each other without being tightly coupled. This guide will walk you through everything you need to know about using events effectively in your Wails application.

Understanding Wails Events

Think of events as messages that get broadcast throughout your application. Any part of your application can listen for these messages and react accordingly. This is particularly useful for:

Responding to window changes: Know when your window is minimized, maximized, or moved
Handling system events: React to theme changes or power events
Custom application logic: Create your own events for features like data updates or user actions
Cross-component communication: Let different parts of your app communicate without direct dependencies

Event Naming Convention

All Wails events follow a namespace pattern to clearly indicate their origin:

common: - Cross-platform events that work on Windows, macOS, and Linux
windows: - Windows-specific events
mac: - macOS-specific events
linux: - Linux-specific events

For example:

common:WindowFocus - Window gained focus (works everywhere)
windows:APMSuspend - System is suspending (Windows only)
mac:ApplicationDidBecomeActive - App became active (macOS only)

Getting Started with Events

Listening to Events (Frontend)

The most common use case is listening for events in your frontend code:

import { Events } from '@wailsio/runtime';

// Listen for when the window gains focus
Events.On('common:WindowFocus', () => {
    console.log('Window is now focused!');
    // Maybe refresh some data or resume animations
});

// Listen for theme changes
Events.On('common:ThemeChanged', (event) => {
    console.log('Theme changed:', event.data);
    // Update your app's theme accordingly
});

// Listen for custom events from your Go backend
Events.On('my-app:data-updated', (event) => {
    console.log('Data updated:', event.data);
    // Update your UI with the new data
});

Emitting Events (Backend)

From your Go code, you can emit events that your frontend can listen to:

package main

import (
    "github.com/wailsapp/wails/v3/pkg/events"
    "github.com/wailsapp/wails/v3/pkg/application"
)

func (a *App) UpdateData() {
    // Do some data processing...

    // Notify the frontend
    a.app.EmitEvent("my-app:data-updated", map[string]interface{}{
        "timestamp": time.Now(),
        "count": 42,
    })
}

Removing Event Listeners

Always clean up your event listeners when they’re no longer needed:

// Store the handler reference
const focusHandler = () => {
    console.log('Window focused');
};

// Add the listener
Events.On('common:WindowFocus', focusHandler);

// Later, remove it when no longer needed
Events.Off('common:WindowFocus', focusHandler);

// Or remove all listeners for an event
Events.Off('common:WindowFocus');

Common Use Cases

1. Pause/Resume on Window Focus

Many applications need to pause certain activities when the window loses focus:

let animationRunning = true;

Events.On('common:WindowLostFocus', () => {
    animationRunning = false;
    pauseBackgroundTasks();
});

Events.On('common:WindowFocus', () => {
    animationRunning = true;
    resumeBackgroundTasks();
});

2. Responding to Theme Changes

Keep your app in sync with the system theme:

Events.On('common:ThemeChanged', (event) => {
    const isDarkMode = event.data.isDark;

    if (isDarkMode) {
        document.body.classList.add('dark-theme');
        document.body.classList.remove('light-theme');
    } else {
        document.body.classList.add('light-theme');
        document.body.classList.remove('dark-theme');
    }
});

3. Handling File Drops

Make your app accept dragged files:

Events.On('common:WindowFilesDropped', (event) => {
    const files = event.data.files;

    files.forEach(file => {
        console.log('File dropped:', file);
        // Process the dropped files
        handleFileUpload(file);
    });
});

4. Window Lifecycle Management

Respond to window state changes:

Events.On('common:WindowClosing', () => {
    // Save user data before closing
    saveApplicationState();

    // You could also prevent closing by returning false
    // from a registered window close handler
});

Events.On('common:WindowMaximise', () => {
    // Adjust UI for maximized view
    adjustLayoutForMaximized();
});

Events.On('common:WindowRestore', () => {
    // Return UI to normal state
    adjustLayoutForNormal();
});

5. Platform-Specific Features

Handle platform-specific events when needed:

// Windows-specific power management
Events.On('windows:APMSuspend', () => {
    console.log('System is going to sleep');
    saveState();
});

Events.On('windows:APMResumeSuspend', () => {
    console.log('System woke up');
    refreshData();
});

// macOS-specific app lifecycle
Events.On('mac:ApplicationWillTerminate', () => {
    console.log('App is about to quit');
    performCleanup();
});

Creating Custom Events

You can create your own events for application-specific needs:

Backend (Go)

// Emit a custom event when data changes
func (a *App) ProcessUserData(userData UserData) error {
    // Process the data...

    // Notify all listeners
    a.app.EmitEvent("user:data-processed", map[string]interface{}{
        "userId": userData.ID,
        "status": "completed",
        "timestamp": time.Now(),
    })

    return nil
}

// Emit periodic updates
func (a *App) StartMonitoring() {
    ticker := time.NewTicker(5 * time.Second)
    go func() {
        for range ticker.C {
            stats := a.collectStats()
            a.app.EmitEvent("monitor:stats-updated", stats)
        }
    }()
}

Frontend (JavaScript)

// Listen for your custom events
Events.On('user:data-processed', (event) => {
    const { userId, status, timestamp } = event.data;

    showNotification(`User ${userId} processing ${status}`);
    updateUIWithNewData();
});

Events.On('monitor:stats-updated', (event) => {
    updateDashboard(event.data);
});

Event Reference

Common Events (Cross-platform)

These events work on all platforms:

Event	Description	When to Use
`common:ApplicationStarted`	Application has fully started	Initialize your app, load saved state
`common:WindowRuntimeReady`	Wails runtime is ready	Start making Wails API calls
`common:ThemeChanged`	System theme changed	Update app appearance
`common:WindowFocus`	Window gained focus	Resume activities, refresh data
`common:WindowLostFocus`	Window lost focus	Pause activities, save state
`common:WindowMinimise`	Window was minimized	Pause rendering, reduce resource usage
`common:WindowMaximise`	Window was maximized	Adjust layout for full screen
`common:WindowRestore`	Window restored from min/max	Return to normal layout
`common:WindowClosing`	Window is about to close	Save data, cleanup resources
`common:WindowFilesDropped`	Files dropped on window	Handle file imports
`common:WindowDidResize`	Window was resized	Adjust layout, rerender charts
`common:WindowDidMove`	Window was moved	Update position-dependent features

Platform-Specific Events

Windows Events

Key events for Windows applications:

Event	Description	Use Case
`windows:SystemThemeChanged`	Windows theme changed	Update app colors
`windows:APMSuspend`	System suspending	Save state, pause operations
`windows:APMResumeSuspend`	System resumed	Restore state, refresh data
`windows:APMPowerStatusChange`	Power status changed	Adjust performance settings

macOS Events

Important macOS application events:

Event	Description	Use Case
`mac:ApplicationDidBecomeActive`	App became active	Resume operations
`mac:ApplicationDidResignActive`	App became inactive	Pause operations
`mac:ApplicationWillTerminate`	App will quit	Final cleanup
`mac:WindowDidEnterFullScreen`	Entered fullscreen	Adjust UI for fullscreen
`mac:WindowDidExitFullScreen`	Exited fullscreen	Restore normal UI

Linux Events

Core Linux window events:

Event	Description	Use Case
`linux:SystemThemeChanged`	Desktop theme changed	Update app theme
`linux:WindowFocusIn`	Window gained focus	Resume activities
`linux:WindowFocusOut`	Window lost focus	Pause activities

Best Practices

1. Use Event Namespaces

When creating custom events, use namespaces to avoid conflicts:

// Good - namespaced events
Events.Emit('myapp:user:login');
Events.Emit('myapp:data:updated');
Events.Emit('myapp:network:connected');

// Avoid - generic names that might conflict
Events.Emit('login');
Events.Emit('update');

2. Clean Up Listeners

Always remove event listeners when components unmount:

// React example
useEffect(() => {
    const handler = (event) => {
        // Handle event
    };

    Events.On('common:WindowResize', handler);

    // Cleanup
    return () => {
        Events.Off('common:WindowResize', handler);
    };
}, []);

3. Handle Platform Differences

Check platform availability when using platform-specific events:

import { Platform } from '@wailsio/runtime';

if (Platform.isWindows) {
    Events.On('windows:APMSuspend', handleSuspend);
} else if (Platform.isMac) {
    Events.On('mac:ApplicationWillTerminate', handleTerminate);
}

4. Don’t Overuse Events

While events are powerful, don’t use them for everything:

✅ Use events for: System notifications, lifecycle changes, broadcast updates
❌ Avoid events for: Direct function returns, single component updates, synchronous operations

Debugging Events

To debug event issues:

// Log all events (development only)
if (isDevelopment) {
    const originalOn = Events.On;
    Events.On = function(eventName, handler) {
        console.log(`[Event Registered] ${eventName}`);
        return originalOn.call(this, eventName, function(event) {
            console.log(`[Event Fired] ${eventName}`, event);
            return handler(event);
        });
    };
}

Source of Truth

The complete list of available events can be found in the Wails source code:

Frontend events: v3/internal/runtime/desktop/@wailsio/runtime/src/event_types.ts
Backend events: v3/pkg/events/events.go

Always refer to these files for the most up-to-date event names and availability.

Summary

Events in Wails provide a powerful, decoupled way to handle communication in your application. By following the patterns and practices in this guide, you can build responsive, platform-aware applications that react smoothly to system changes and user interactions.

Remember: start with common events for cross-platform compatibility, add platform-specific events when needed, and always clean up your event listeners to prevent memory leaks.