如何使用代码进行联系备份？

As we all know that, when we click the option "export to SD card" in contacts, , It means we are creating our contact backup and that file is stored with the extension as a .VCF file format, Later on when we import that file, android OS automatically takes all the contacts in it and saves in our contacts. I just want to create that .VCF (A Contacts backup file) using code.As we all know that, when we click the option "