wailsapp/wails · error · Error

Invalid JSON passed to Notify: ${notifyMessage}

Error message

Invalid JSON passed to Notify: ${notifyMessage}

What it means

SelectObject wraps gdi32.SelectObject, which selects a GDI object (pen, brush, font, bitmap) into a device context and returns the previously selected object. The w32 wrapper panics with 'SelectObject failed' when the API returns NULL/0. Windows returns failure when the handle is not a valid GDI object, does not match a type the DC accepts, or has already been deleted — a classic use-after-delete bug. Note the wrapper's zero check is also technically lossy for regions, where the error return is HGDI_ERROR rather than NULL.

Source

Thrown at v2/internal/frontend/runtime/desktop/events.js:132

        }
    }
}

/**
 * Notify informs frontend listeners that an event was emitted with the given data
 *
 * @export
 * @param {string} notifyMessage - encoded notification message

 */
export function EventsNotify(notifyMessage) {
    // Parse the message
    let message;
    try {
        message = JSON.parse(notifyMessage);
    } catch (e) {
        const error = 'Invalid JSON passed to Notify: ' + notifyMessage;
        throw new Error(error);
    }
    notifyListeners(message);
}

/**
 * Emit an event with the given name and data
 *
 * @export
 * @param {string} eventName
 */
export function EventsEmit(eventName) {

    const payload = {
        name: eventName,
        data: [].slice.apply(arguments).slice(1),
    };

    // Notify JS listeners

View on GitHub (pinned to 0e754b1b40)

Solutions

1. Ensure the object being selected was created (CreateSolidBrush, CreateCompatibleBitmap, ...) and not deleted; search for DeleteObject calls on shared objects.
2. Follow the save/restore idiom: store the return value (the old object) and re-select it before deleting your object and the DC.
3. Never have one HBITMAP selected into two DCs simultaneously; create one compatible bitmap per DC.
4. Confirm the object type matches what the DC expects at that slot (bitmap only into memory DCs).
5. Run with Application Verifier or GDI diagnostic tools (e.g. GDIView) to find which handle is dead at selection time.

Example fix

// before
old := w32.SelectObject(hdcMem, hbm)
w32.DeleteObject(hbm) // still selected in another DC -> later SelectObject panics

// after
old := w32.SelectObject(hdcMem, hbm)
defer w32.SelectObject(hdcMem, old) // restore first
// ... draw ...
w32.DeleteObject(hbm) // delete only after restore

func safeSelect(hdc w32.HDC, obj w32.HGDIOBJ) (old w32.HGDIOBJ, err error) {
	defer func() {
		if r := recover(); r != nil {
			err = fmt.Errorf("SelectObject: %v (object deleted or wrong type?)", r)
		}
	}()
	return w32.SelectObject(hdc, obj), nil
}

When it happens

Trigger: Selecting a bitmap/pen/brush that was already passed to DeleteObject; selecting a bitmap into more than one memory DC at a time (GDI forbids this); passing a handle of the wrong type (e.g. an HBRUSH where an HBITMAP is required); using a DC after DeleteDC.

Common situations: Double-buffering code that deletes the old bitmap but keeps selecting it again on the next frame; cleanup routines that delete brushes still selected into a live DC; porting drawing code from C where the old object restore order was accidental but tolerated.

Understand the failure class

• Parsing and encoding errors: unexpected token, malformed input — why parsers reject input and how to find the real culprit.

Related errors

• Invalid JSON passed to callback: ${e.message}. Message: ${in
• Callback '${callbackID}' not registered!!!
• CancellablePromise does not support transparent subclassing.
• CancellablePromise.prototype.then called on an invalid objec
• CancellablePromise.prototype.finally called on an invalid ob

AI-assisted analysis of wailsapp/wails@0e754b1b40 (2026-08-15). Data as JSON: /api/errors/5f6728c323671d56. Report an issue: GitHub.