The Android MediaStore maintains the metadata of audio, video and image files in the underlying filesystem for convenient consumption by relevant Android apps (eg. music player).
The problem is when manipulating the SD card content with an Android file manager, sometimes the metadata cache becomes out of sync with the actual filesystem. So for example if you rename or delete a folder using a file manager, then connect the device via a USB cable to your PC to be accessed via MTP, the old folder may appear in Windows Explorer. Clicking "Refresh" does not work to update the content. The only way to refresh the cache is to reboot the device.
Another method I found recently is to run an app that forces MediaStore to refresh its cache. There are many apps available for this purpose if you search for "rescan sd" in the app store. A lot of them won't work with Android 6.x (Mashmallow) and will crash when you try. One ad-free app that works under Mashmallow is Rescan SD Card.
It is a very simple app, but it does take a while to rescan the entire SD card. For my case with a few thousand files, it took 3 to 4 minutes to complete the process.
On the topic of MTP, it is a horrible protocol for file transfer. We used to have USB mass storage, where the SD card is mounted as a drive under Windows Explorer. But this is all but gone in the latest devices and can only be found in some custom ROMs.
Anyway, mounting the SD card as a drive has its own problems because it needs to dismount the storage from Android apps during the usage duration, which can cause all sorts of unexpected problems. Recent devices mostly only support PTP (which is practically useless for anything) and MTP.
MTP is horrible because it is extremely finicky. It can hang when transferring large files. It can hang when you are just renaming a folder. When it hangs, the only workaround is to reboot the device.
Why not use wireless? Wireless transfer apps such as AirDroid or SendAnywhere is not practical when you are trying to transfer large files (eg. video files > 500MB). In addition, when you are out and about, and your PC is connected to a WiFi hotspot, while your phone is connected to 4G, it is a pain to juggle the connections so that the quota on your 4G broadband will not be affected. Simplest is to use a USB cable, which is fast and reliable. Too bad the underlying protocol is garbage.
We need a better standard for wired file transfer over USB, and so far none is forthcoming.
The problem is when manipulating the SD card content with an Android file manager, sometimes the metadata cache becomes out of sync with the actual filesystem. So for example if you rename or delete a folder using a file manager, then connect the device via a USB cable to your PC to be accessed via MTP, the old folder may appear in Windows Explorer. Clicking "Refresh" does not work to update the content. The only way to refresh the cache is to reboot the device.
Another method I found recently is to run an app that forces MediaStore to refresh its cache. There are many apps available for this purpose if you search for "rescan sd" in the app store. A lot of them won't work with Android 6.x (Mashmallow) and will crash when you try. One ad-free app that works under Mashmallow is Rescan SD Card.
It is a very simple app, but it does take a while to rescan the entire SD card. For my case with a few thousand files, it took 3 to 4 minutes to complete the process.
On the topic of MTP, it is a horrible protocol for file transfer. We used to have USB mass storage, where the SD card is mounted as a drive under Windows Explorer. But this is all but gone in the latest devices and can only be found in some custom ROMs.
Anyway, mounting the SD card as a drive has its own problems because it needs to dismount the storage from Android apps during the usage duration, which can cause all sorts of unexpected problems. Recent devices mostly only support PTP (which is practically useless for anything) and MTP.
MTP is horrible because it is extremely finicky. It can hang when transferring large files. It can hang when you are just renaming a folder. When it hangs, the only workaround is to reboot the device.
Why not use wireless? Wireless transfer apps such as AirDroid or SendAnywhere is not practical when you are trying to transfer large files (eg. video files > 500MB). In addition, when you are out and about, and your PC is connected to a WiFi hotspot, while your phone is connected to 4G, it is a pain to juggle the connections so that the quota on your 4G broadband will not be affected. Simplest is to use a USB cable, which is fast and reliable. Too bad the underlying protocol is garbage.
We need a better standard for wired file transfer over USB, and so far none is forthcoming.
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