Dear Chrlie,
Thanks for your support.
After few hours of debugging I realized the root cause of blocking https in my application and I resolved the attachment opening issue as well. To fix the attachment opening issue I changed the value of SAPKapselHandleHttpRequests in to true.
If the value of SAPKapselHandleHttpRequests is true, After login to the application the app will set some proxy values in the fiori client so its blocking all https requests. That's why my all https requests failed. To solve this I added some line of codes to by pass the proxy from android device and now both working fine.
Regards,
Shafi