all product showing Warning: Creating default object from empty value error

-- HikaShop version -- : Hikashop 3.0
-- Joomla version -- : joomla 3.7.8

Hi,

Our product listing layout and product detail all suddenly show an error Warning: Creating default object from empty value. please advice how can i fix this issue?

Hi,

As you can see the error comes from a file of the template, not HikaShop:
monosnap.com/file/jnaMpLfzhborTJULk0hJBS6QMFyeip
So I can't say how to fix as I don't know what is in that mainstep.php file. You should report the issue to your template provider.
Now, please note that Joomla has a "error reporting" setting in its configuration that you can disable ( it's even better to have it disabled on live websites ) and it should normally remove such error messages.