Window Events

Window Events

Wails dispatches window lifecycle and state-change events through a single API: OnWindowEvent for passive listeners, and RegisterHook for cancellable hooks that can prevent the default action.

import "github.com/wailsapp/wails/v3/pkg/events"

// Listener — observes the event, cannot cancel it.
window.OnWindowEvent(events.Common.WindowDidResize, func(e *application.WindowEvent) { /* ... */ })

// Hook — runs before listeners; can call e.Cancel() to suppress the default action.
window.RegisterHook(events.Common.WindowClosing, func(e *application.WindowEvent) {
    if hasUnsavedChanges() {
        e.Cancel() // prevent the window from closing
    }
})

Both calls return an unsubscribe func() you can call to remove the handler.

Cross-platform events live in events.Common.*. Platform-specific events live in events.Mac.*, events.Windows.*, and events.Linux.*. The full list is generated in v3/pkg/events/events.go.

Lifecycle Events

Window Creation

Run a callback every time a window is created using app.Window.OnCreate:

app.Window.OnCreate(func(window application.Window) {
    fmt.Printf("Window created: %s (ID: %d)\n", window.Name(), window.ID())

    // Configure all new windows
    window.SetMinSize(400, 300)

    // Register a hook for this window
    window.RegisterHook(events.Common.WindowClosing, func(e *application.WindowEvent) {
        if !confirmClose() {
            e.Cancel()
        }
    })
})

The callback receives application.Window (an interface). The OnCreate callback is invoked once per window, after the window’s runtime is initialised.

WindowClosing

Fires when the user attempts to close the window (clicking X, ⌘W, Alt+F4, etc.).

Use a hook (RegisterHook) — only hooks can cancel the close. Listeners observe the event but cannot prevent it.

window.RegisterHook(events.Common.WindowClosing, func(e *application.WindowEvent) {
    if hasUnsavedChanges() {
        // Cancel the close — the window stays open.
        e.Cancel()
    }
})

Important:

• WindowClosing is dispatched on user-initiated close attempts.
• A RegisterHook callback can call e.Cancel() to keep the window open.
• OnWindowEvent callbacks for WindowClosing are observers — they fire but cannot cancel.

Programmatic close: call window.Close(). There is no window.Destroy().

WindowRuntimeReady

Fires once the in-window runtime has finished initialising — safe point to call into the window’s JS context:

window.OnWindowEvent(events.Common.WindowRuntimeReady, func(e *application.WindowEvent) {
    window.EmitEvent("app-ready", nil)
})

Focus Events

WindowFocus

Called when the window gains focus:

window.OnWindowEvent(events.Common.WindowFocus, func(e *application.WindowEvent) {
    fmt.Println("Window gained focus")
    updateTitleBar(true)
    app.Event.Emit("window-focused", window.ID())
})

WindowLostFocus

Called when the window loses focus:

window.OnWindowEvent(events.Common.WindowLostFocus, func(e *application.WindowEvent) {
    fmt.Println("Window lost focus")
    updateTitleBar(false)
    saveCurrentState()
})

Example: Focus-aware UI:

type FocusAwareWindow struct {
    window  *application.WebviewWindow
    focused bool
}

func (fw *FocusAwareWindow) Setup() {
    fw.window.OnWindowEvent(events.Common.WindowFocus, func(e *application.WindowEvent) {
        fw.focused = true
        fw.updateAppearance()
    })

    fw.window.OnWindowEvent(events.Common.WindowLostFocus, func(e *application.WindowEvent) {
        fw.focused = false
        fw.updateAppearance()
    })
}

func (fw *FocusAwareWindow) updateAppearance() {
    if fw.focused {
        fw.window.EmitEvent("update-theme", "active")
    } else {
        fw.window.EmitEvent("update-theme", "inactive")
    }
}

State Change Events

WindowMinimise / WindowUnMinimise

window.OnWindowEvent(events.Common.WindowMinimise, func(e *application.WindowEvent) {
    pauseRendering()
    saveWindowState()
})

window.OnWindowEvent(events.Common.WindowUnMinimise, func(e *application.WindowEvent) {
    resumeRendering()
    refreshContent()
})

WindowMaximise / WindowUnMaximise

window.OnWindowEvent(events.Common.WindowMaximise, func(e *application.WindowEvent) {
    window.EmitEvent("layout-mode", "maximised")
})

window.OnWindowEvent(events.Common.WindowUnMaximise, func(e *application.WindowEvent) {
    window.EmitEvent("layout-mode", "normal")
})

WindowFullscreen / WindowUnFullscreen

window.OnWindowEvent(events.Common.WindowFullscreen, func(e *application.WindowEvent) {
    window.EmitEvent("chrome-visibility", false)
    window.EmitEvent("layout-mode", "fullscreen")
})

window.OnWindowEvent(events.Common.WindowUnFullscreen, func(e *application.WindowEvent) {
    window.EmitEvent("chrome-visibility", true)
    window.EmitEvent("layout-mode", "normal")
})

Enter/exit fullscreen programmatically with window.Fullscreen() / window.UnFullscreen() / window.ToggleFullscreen() — there is no SetFullscreen(bool). Query state with window.IsFullscreen() bool.

Position and Size Events

WindowDidMove

window.OnWindowEvent(events.Common.WindowDidMove, func(e *application.WindowEvent) {
    x, y := window.Position()
    fmt.Printf("Window moved to: %d, %d\n", x, y)
    saveWindowPosition(x, y)
})

WindowDidResize

window.OnWindowEvent(events.Common.WindowDidResize, func(e *application.WindowEvent) {
    width, height := window.Size()
    fmt.Printf("Window resized to: %dx%d\n", width, height)
    saveWindowSize(width, height)
    window.EmitEvent("window-size", map[string]int{
        "width":  width,
        "height": height,
    })
})

WindowDidResize and WindowDidMove do not carry coordinates on the event itself — query the window via window.Size() / window.Position() inside the callback.

Example: Responsive layout:

window.OnWindowEvent(events.Common.WindowDidResize, func(e *application.WindowEvent) {
    width, _ := window.Size()
    var layout string
    switch {
    case width < 600:
        layout = "compact"
    case width < 1200:
        layout = "normal"
    default:
        layout = "wide"
    }
    window.EmitEvent("layout-changed", layout)
})

Complete Example

A production-ready window with full event handling:

package main

import (
    "encoding/json"
    "fmt"
    "os"

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

type WindowState struct {
    X          int  `json:"x"`
    Y          int  `json:"y"`
    Width      int  `json:"width"`
    Height     int  `json:"height"`
    Maximised  bool `json:"maximised"`
    Fullscreen bool `json:"fullscreen"`
}

type ManagedWindow struct {
    app    *application.App
    window *application.WebviewWindow
    state  WindowState
    dirty  bool
}

func main() {
    app := application.New(application.Options{
        Name: "Event Demo",
    })

    mw := &ManagedWindow{app: app}
    mw.CreateWindow()
    mw.LoadState()
    mw.SetupEventHandlers()

    app.Run()
}

func (mw *ManagedWindow) CreateWindow() {
    mw.window = mw.app.Window.NewWithOptions(application.WebviewWindowOptions{
        Name:   "main",
        Title:  "Event Demo",
        Width:  800,
        Height: 600,
    })
}

func (mw *ManagedWindow) SetupEventHandlers() {
    // Focus events
    mw.window.OnWindowEvent(events.Common.WindowFocus, func(e *application.WindowEvent) {
        mw.window.EmitEvent("focus-state", true)
    })

    mw.window.OnWindowEvent(events.Common.WindowLostFocus, func(e *application.WindowEvent) {
        mw.window.EmitEvent("focus-state", false)
    })

    // State change events
    mw.window.OnWindowEvent(events.Common.WindowMinimise, func(e *application.WindowEvent) {
        mw.SaveState()
    })

    mw.window.OnWindowEvent(events.Common.WindowMaximise, func(e *application.WindowEvent) {
        mw.state.Maximised = true
        mw.dirty = true
    })

    mw.window.OnWindowEvent(events.Common.WindowUnMaximise, func(e *application.WindowEvent) {
        mw.state.Maximised = false
        mw.dirty = true
    })

    mw.window.OnWindowEvent(events.Common.WindowFullscreen, func(e *application.WindowEvent) {
        mw.state.Fullscreen = true
        mw.dirty = true
    })

    mw.window.OnWindowEvent(events.Common.WindowUnFullscreen, func(e *application.WindowEvent) {
        mw.state.Fullscreen = false
        mw.dirty = true
    })

    // Position and size events
    mw.window.OnWindowEvent(events.Common.WindowDidMove, func(e *application.WindowEvent) {
        mw.state.X, mw.state.Y = mw.window.Position()
        mw.dirty = true
    })

    mw.window.OnWindowEvent(events.Common.WindowDidResize, func(e *application.WindowEvent) {
        mw.state.Width, mw.state.Height = mw.window.Size()
        mw.dirty = true
    })

    // Cancellable close — use a hook, not a listener.
    mw.window.RegisterHook(events.Common.WindowClosing, func(e *application.WindowEvent) {
        if mw.dirty {
            mw.SaveState()
        }
    })
}

func (mw *ManagedWindow) LoadState() {
    data, err := os.ReadFile("window-state.json")
    if err != nil {
        return
    }

    if err := json.Unmarshal(data, &mw.state); err != nil {
        return
    }

    // Restore window state
    mw.window.SetPosition(mw.state.X, mw.state.Y)
    mw.window.SetSize(mw.state.Width, mw.state.Height)

    if mw.state.Maximised {
        mw.window.Maximise()
    }

    if mw.state.Fullscreen {
        mw.window.Fullscreen()
    }
}

func (mw *ManagedWindow) SaveState() {
    data, err := json.Marshal(mw.state)
    if err != nil {
        return
    }

    os.WriteFile("window-state.json", data, 0644)
    mw.dirty = false

    fmt.Println("Window state saved")
}

Event Coordination

Cross-Window Events

Coordinate between multiple windows using the application event bus:

// In main window
mainWindow.OnWindowEvent(events.Common.WindowFocus, func(e *application.WindowEvent) {
    app.Event.Emit("main-window-focused", nil)
})

// In other windows
app.Event.On("main-window-focused", func(event *application.CustomEvent) {
    updateRelativeToMain()
})

Event Chains

window.OnWindowEvent(events.Common.WindowMaximise, func(e *application.WindowEvent) {
    saveWindowState()
    window.EmitEvent("layout-changed", "maximised")
    app.Event.Emit("window-maximised", window.ID())
})

Debounced Events

var resizeTimer *time.Timer

window.OnWindowEvent(events.Common.WindowDidResize, func(e *application.WindowEvent) {
    if resizeTimer != nil {
        resizeTimer.Stop()
    }

    resizeTimer = time.AfterFunc(500*time.Millisecond, func() {
        w, h := window.Size()
        saveWindowSize(w, h)
    })
})

Best Practices

✅ Do

• Use hooks for cancellation — only RegisterHook callbacks can call e.Cancel().
• Save state on close — restore window position/size next launch.
• Debounce frequent events — WindowDidResize and WindowDidMove fire rapidly.
• Handle focus changes — update UI appropriately.
• Coordinate via events — app.Event.Emit for cross-window messaging.
• Unsubscribe when handlers are no longer needed — OnWindowEvent/RegisterHook both return an unsubscribe func().

❌ Don’t

• Don’t block event handlers — keep them fast.
• Don’t try to cancel from OnWindowEvent — use RegisterHook.
• Don’t use window.Destroy() — it doesn’t exist; use window.Close().
• Don’t save on every event — debounce first.
• Don’t assume coordinates on the event — call window.Position() / window.Size().

Troubleshooting

WindowClosing Hook Doesn’t Prevent Close

Cause: You used OnWindowEvent instead of RegisterHook.

Solution: Only RegisterHook callbacks can call e.Cancel(). OnWindowEvent callbacks observe; they cannot cancel.

// ❌ Cannot cancel — this is a listener.
window.OnWindowEvent(events.Common.WindowClosing, func(e *application.WindowEvent) {
    e.Cancel() // no effect
})

// ✅ Can cancel — this is a hook.
window.RegisterHook(events.Common.WindowClosing, func(e *application.WindowEvent) {
    e.Cancel()
})

Events Not Firing

Cause: Handler registered after the event occurred.

Solution: Register handlers immediately after window creation (or in the app.Window.OnCreate callback).

window := app.Window.New()
window.OnWindowEvent(events.Common.WindowFocus, func(e *application.WindowEvent) { /* ... */ })

Memory Leaks

Cause: Long-lived handlers held by short-lived state.

Solution: Keep the unsubscribe func() returned by OnWindowEvent/RegisterHook and call it during cleanup.

unsub := window.OnWindowEvent(events.Common.WindowDidResize, handler)
// ...later:
unsub()

Next Steps

Window Basics - Learn the fundamentals of window management Learn More →

Multiple Windows - Patterns for multi-window applications Learn More →

Events System - Deep dive into the event system Learn More →

Application Lifecycle - Understand the application lifecycle Learn More →

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Questions? Ask in Discord or check the examples.