How can I send an NSString to the currently focused UIElement of another application?

I have a menubar application without a dock icon or global menu, it's just a StatusItem and a Window.

I've got it wired up to a hotkey which activates the window and upon deactivating the window I am able to send focus back to the previously active application.

How can I send an NSString to the active textarea in the other application, as if the user had typed it directly?

I think it might be possible using accessibility features. I'd like to avoid using AppleScript if at all possible.

Solution

I ended up using the pasteboard and CGEventCreateKeyboardEvent() to mimic the [cmd+v] keyboard shortcut for pasting.

Before activating my window, I record the previous application:

_previousApplication = [[notification userInfo] objectForKey:NSWorkspaceApplicationKey];

After I dismiss my window, I activate the previous application:

[_previousApplication activateWithOptions:NSApplicationActivateIgnoringOtherApps];

Then paste the NSString:

#define KEY_CODE_v ((CGKeyCode)9)

void DCPostCommandAndKey(CGKeyCode key) {
    CGEventSourceRef source = CGEventSourceCreate(kCGEventSourceStateCombinedSessionState);

    CGEventRef keyDown = CGEventCreateKeyboardEvent(source, key, TRUE);
    CGEventSetFlags(keyDown, kCGEventFlagMaskCommand);
    CGEventRef keyUp = CGEventCreateKeyboardEvent(source, key, FALSE);

    CGEventPost(kCGAnnotatedSessionEventTap, keyDown);
    CGEventPost(kCGAnnotatedSessionEventTap, keyUp);

    CFRelease(keyUp);
    CFRelease(keyDown);
    CFRelease(source);
}

DCPostCommandAndKey(KEY_CODE_v);