You may apply H4 visa in China though you hold AP. If you show the INS officer the AP to re-enter, then you will not be admitted as an H-visa holder.In this way, a denial of the I-140 Petition would have effects on your present lawful nonimmigrant status. Whether using AP or applying for H4 visa may depend on your present situation. If your hu*****and's I140 has been approved, you may just use AP.
Actually, I have the same question as yours. Now I am not sure if I transfer my H1b, how will it influence H4 visa application? If you get some information, would you please let me know too? Thanks.