method at

Source

static bool at(BuildContext context, { bool autofocus: false }) {
  assert(context != null);
  assert(context.widget != null);
  assert(context.widget.key != null);
  assert(context.widget.key is GlobalKey);
  _FocusScope focusScope = context.inheritFromWidgetOfExactType(_FocusScope);
  if (focusScope != null) {
    if (autofocus)
      focusScope._setFocusedWidgetIfUnset(context.widget.key);
    return focusScope.scopeFocused &&
           focusScope.focusedScope == null &&
           focusScope.focusedWidget == context.widget.key;
  }
  assert(() {
    if (debugOnlyFocusedKey?.currentContext == null)
      debugOnlyFocusedKey = context.widget.key;
    if (debugOnlyFocusedKey != context.widget.key) {
      throw new FlutterError(
        'Missing Focus scope.\n'
        'Two focusable widgets with different keys, $debugOnlyFocusedKey and ${context.widget.key}, '
        'exist in the widget tree simultaneously, but they have no Focus widget ancestor.\n'
        'If you have more than one focusable widget, then you should put them inside a Focus. '
        'Normally, this is done for you using a Route, via Navigator, WidgetsApp, or MaterialApp.'
      );
    }
    return true;
  });
  return true;
}