Is there a way to access files of an Android device from another Android device using Wi-Fi? I need something like a file explorer.
Generally, any good file explorer with FTP, SFTP, WebDAV, and SMB/CIFS capabilities can handle this task with ease or other Wi-Fi file-sharing applications. You can even browse through Play Store to get the right one, e.g. Solid Explorer, Total Commander etc. For starters, you can run through Izzy's list of Filetransfer between two Android devices.
For purposes of explanation, I chose ES Explorer, it has a lot of functions including remote browser:
You can use the following procedure to access files in another device:
Install ES Explorer on both devices if you haven't already done so.
Switch on a portable hotspot and allow both devices to connect.
Using phone A, open ES Explorer and go to remote manager and turn it on. See below:
(click image for larger variant)
Copy the server details from phone A, you will need them in phone B.
Using phone B, open ES Explorer and navigate to Network → FTP.
Add a new server using the details you previously copied:
When setup is completed, you can now browse the files of phone A from phone B.
See screens from both devices:
(click images for larger variants)
Connect two Android devices without a router via Wifi Direct.
Wi-Fi peer-to-peer (P2P) allows Android 4.0 (API level 14) or later devices with the appropriate hardware to connect directly to each other via Wi-Fi without an intermediate access point (Android's Wi-Fi P2P framework complies with the Wi-Fi Alliance's Wi-Fi Direct™ certification program).
I watched the above video to reproduce the steps. Unfortunately, my 4.2.2 Android tablet shows no menu item for WiFi Direct. Asked my friend to check and his Samsung smartphone Android 5.0 shows a router option and none for WiFi Direct. All I can select from my tablet's Settings/WiFi/other is Hotspot for Internet access sharing/tethering.
My interest is to stream videos from one Android Tablet to another Android Tablet over WiFi Direct. WiFi Direct specification and manual are about 180 pages long. Not sure how to enable WiFi Direct on my tablet.
Anyway, I can still connect from my tablet to P2P (WiFi Direct) camera to watch live video feeds. So if both of your Android devices support WiFi Direct connection, the above video comes with a solution to your question.
The best app I've found is X-plore File Manager. It has a WiFi file server and can browse the SD card and internal card of another phone on the same WiFi. The best part is it works both on someone's hotspot and if you are the hotspot as well.