[flutter-chat-demo].dart

@override
Widget build(BuildContext context) {
  return Scaffold(
    appBar: AppBar(
      title: Text(
        this.widget.arguments.peerNickname,
        style: TextStyle(color: ColorConstants.primaryColor),
      ),
      centerTitle: true,
    ),
    body: SafeArea(
      child: PopScope(
        child: Stack(
          children: [
            Column(
              children: [
                _buildListMessage(),
                _isShowSticker ? _buildStickers() : SizedBox.shrink(),
                _buildInput(),
              ],
            ),
            Positioned(
              child: _isLoading ? LoadingView() : SizedBox.shrink(),
            ),
          ],
        ),
        canPop: false,
        onPopInvoked: (didPop) {
          if (didPop) return;
          _onBackPress();
        },
      ),
    ),
  );
}