display showDialog when a value is changed in provider

Question

I have a boolean variable in my model class that extends ChangeNotifier, when the value of this variable changes I want to show a dialog and pop this dialog when it changes to false. Code that I am using:

Widget selectedFiles() {
    return Consumer<FilesManager>(
      builder: (context, filesManager, child) {
        if (filesManager.processingFiles != null) {
          filesManager.processingFiles == true
              ? showAlertDialog(context)
              : Navigator.pop(context);
        }
        return Expanded(
          child: ListView.builder(
              itemCount: filesManager.files.length,
              itemBuilder: (context, index) {
                return ListTile(
                  title: Text(p.basename(filesManager.files[index].path)),
                );
              }),
        );
      },
    );
  }

When I set processingFiles to true I want to display an alertDialog.