wailsapp/wails · error

IconType is invalid

Error message

IconType is invalid

What it means

Form.SetIcon maps iconType to WM_SETICON's wParam, which accepts only 0 (ICON_SMALL) or 1 (ICON_BIG); any value above 1 panics with 'IconType is invalid'. This is pure input validation before the SendMessage — nothing Windows-related can fail here. The panic is always a caller bug: passing an icon index, size, or enum from another API.

Source

Thrown at v2/internal/frontend/desktop/windows/winc/form.go:222

	if !fm.isFullscreen {
		return
	}
	w32.SetWindowLong(fm.hwnd, w32.GWL_STYLE, fm.previousWindowStyle)
	w32.SetWindowLong(fm.hwnd, w32.GWL_EXSTYLE, fm.previousWindowExStyle)
	w32.SetWindowPlacement(fm.hwnd, &fm.previousWindowPlacement)
	fm.isFullscreen = false
	w32.SetWindowPos(fm.hwnd, 0, 0, 0, 0, 0,
		w32.SWP_NOMOVE|w32.SWP_NOSIZE|w32.SWP_NOZORDER|w32.SWP_NOOWNERZORDER|w32.SWP_FRAMECHANGED)
}

func (fm *Form) IsFullScreen() bool {
	return fm.isFullscreen
}

// IconType: 1 - ICON_BIG; 0 - ICON_SMALL
func (fm *Form) SetIcon(iconType int, icon *Icon) {
	if iconType > 1 {
		panic("IconType is invalid")
	}
	w32.SendMessage(fm.hwnd, w32.WM_SETICON, uintptr(iconType), uintptr(icon.Handle()))
}

func (fm *Form) EnableMaxButton(b bool) {
	SetStyle(fm.hwnd, b, w32.WS_MAXIMIZEBOX)
}

func (fm *Form) EnableMinButton(b bool) {
	SetStyle(fm.hwnd, b, w32.WS_MINIMIZEBOX)
}

func (fm *Form) EnableSizable(b bool) {
	SetStyle(fm.hwnd, b, w32.WS_THICKFRAME)
}

func (fm *Form) EnableDragMove(_ bool) {
	//fm.isDragMove = b

View on GitHub (pinned to 0e754b1b40)

Solutions

1. Use only the two documented constants: w32.ICON_BIG (1) for the alt-tab/taskbar icon and w32.ICON_SMALL (0) for the title-bar icon
2. Set both: SetIcon(w32.ICON_BIG, icoBig) and SetIcon(w32.ICON_SMALL, icoSmall) — for other sizes register icons in the window class or via the exe resource
3. If multiple resolutions are needed, embed them as a single multi-size .ico resource instead of extra SetIcon calls

Example fix

// before
form.SetIcon(32, icon) // 32 > 1 -> panic

// after
form.SetIcon(w32.ICON_BIG, icon)
form.SetIcon(w32.ICON_SMALL, icon)

func validIconType(t int) bool { return t == 0 || t == 1 } // ICON_SMALL / ICON_BIG

func iconTypeValid(t int) bool { return t == int(w32.ICON_SMALL) || t == int(w32.ICON_BIG) }

When it happens

Trigger: Calling form.SetIcon(2, ico) or higher; passing an icon dimension like 32/256 as iconType; confusing this API with per-DPI icon setting (WM_SETICON has no DPI variants).

Common situations: Wrapping SetIcon in a loop over icon sizes; porting code from frameworks where icon 'type' enums have more members.

Related errors

• GetSysColorBrush failed
• missing icon with icon ID: %d
• Cannot create canvas from invalid HDC.
• cannot create window for " + className
• Invalid font style

AI-assisted analysis of wailsapp/wails@0e754b1b40 (2026-08-15). Data as JSON: /api/errors/f7fc4d9716a90a33. Report an issue: GitHub.