I am working on a project where a .Net application stores data on phones SD card. I need to read the data and display in notification. But the problem is that my application Can't read the sd card when my phone is connected in Mass Storage mode. And .Net application can't store data im MTP mode. I dont want my android device to detach from the PC but want to read the SD card.
No. In mass storage mode the phone effectively acts as a card reader, so the PC has complete control over it. If the phone were to mount the card at the same time as the PC, the filesystem on the card would become corrupted. That's why Android phones don't offer USB mass storage any more.
With MTP, the PC goes through what's effectively a file server on the Android phone, instead of mounting the card's filesystem completely. That way, the phone still has access to the card, and the phone can control what the PC can access.