问构建期间调用的颤振visitChildElements()

EN

final ApiServiceController uController = Get.put(ApiServiceController());

downloading(String fileUrl, String fileName) async {
    Dio dio = Dio();
    fToast("Downloading... $fileName", pop);

    try {
      var dir = await downloadDirectory();
      uController.isDwd.value = true;

      await dio.download(fileUrl, "${dir.path}/$fileName",
          onReceiveProgress: (rec, total) {
        print("Rec: $rec , Total: $total");

        uController.dwdP.value = ((rec / total) * 100).toStringAsFixed(0) + "%";
      });
      fToast("Downloaded", pop);
    } catch (e) {
      print(e);
    }
    uController.isDwd.value = false;

    print("Download completed");
  }

Stack(children: [
///.. Container widget here,
Obx(() {
    return uController.isDwd.value
        ? loading(context, uController.dwdP.value)
        : SizedBox(height: 0);
  })
])

════════ Exception caught by widgets library ═══════════════════════════════════
The following assertion was thrown building Obx(has builder, dirty, state: _ObxState#291e4):
visitChildElements() called during build.

The BuildContext.visitChildElements() method can't be called during build because the child list is still being updated at that point, so the children might not be constructed yet, or might be old children that are going to be replaced.
The relevant error-causing widget was
Obx

WidgetsBinding.instance.addPostFrameCallback((_) {
      // executes after build
});