Develop Reference

How to access files on an attached USB flash drive [Android 12]

I am trying to read files from an attached USB flash drive, I have scoured through countless Stackoverflow questions and nothing is working.
I am able to detect when a USB is attached and I know that the USB is mounted under
/mnt/media_rw/
and I'm able to get this path using StorageManager but the system denies my app permission to read any files under that path even after adding all the needed permissions to the manifest
<uses-permission android:name="android.permission.USB_PERMISSION" />
<uses-permission android:name="android.permission.MANAGE_EXTERNAL_STORAGE" />
<uses-permission android:name="android.permission.READ_EXTERNAL_STORAGE" />
According to the documentation "MANAGE_EXTERNAL_STORAGE" permission should give me access to all files on a storage device:
The MANAGE_EXTERNAL_STORAGE permission grants the following:
Read and write access to all files within shared storage.
Access to the contents of the MediaStore.Files table.
Access to the root directory of both the USB on-the-go (OTG) drive and the SD card.
Write access to all internal storage directories⁠, except for /Android/data/, /sdcard/Android, and most subdirectories of /sdcard/Android. This write access includes direct file path access.
https://developer.android.com/training/data-storage/manage-all-files
My question is very simple, all I want is a way to read files from an attached USB flash drive

You should let the user choose the usb drive with ACTION_OPEN_DOCUMENT_TREE.
After that you can browse the whole drive and have access to all files.

How can I write (make directory, write file, ...) on a real sd card

I want to create a folder and write a file in real external storage (real extern sd card).
I can write to the internal storage, the external storage, but not to the external sd card (I mean the external storage card you put into a cell phone for more space to store images, videos, ...).
The path of the external sd-card is: "/storage/1234-5678/" and it is on a samsung smartphone.
Reading from the external sd card works without problems.
I am testing with Android 8 (and later with higher versions).
I have searched through internet and try but not getting the result, I have added permissions in Android Manifest file as well.
<uses-permission android:name="android.permission.READ_EXTERNAL_STORAGE" />
<uses-permission
android:name="android.permission.WRITE_EXTERNAL_STORAGE"
android:maxSdkVersion="29"
tools:ignore="ScopedStorage" />
and an easy test is:
File directory = new File("/storage/1234-5678/new_folder/");
if (!directory.exists()) {
boolean ok = directory.mkdirs();
}
The result to ok is always false, when I use the path to the external / removable sd card.
What I am doing wrong?

Since providing a direct path might be a problem. So I would recommend using the Android file access mechanism.
Mentioned here->https://developer.android.com/training/data-storage/app-specific#external-select-location

Have a look at the second item returned by getExternalFilesDirs().
You can write on that location of the removable micro sd card.

Cannot write to sd card on android

I have an issue with writing to sd card on my android 4.4 device. I'm writing an application that gets path to its directory on sd card using the getExternalFilesDirs() method. But when I try to store data in the directory I get an error:
EACCES (Permisson denied)
The applications directories in Android/data/ in both internal memory and on the sd card are owned by different linux users. Any other application on my device works fine. The application works on another device with that sd card.

You need to add this permission in AndroidManifest.xml:
<uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE" />

i think you have missplaced this line.
Double check this line
<uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE" />
where you have put this line?
this line should be outside of <application/> scope
like this
<manifest>
<uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE"/>
...
<application>
...
<activity>
...
</activity>
</application>
</manifest>
For getExternalFilesDirs to return the path of the sdcard, the OEM must have set the SECONDARY_STORAGE environment variable in the device specific init.rc file as mentioned here: https://source.android.com/devices/storage/config-example.html
Look at the source of getExternalFilesDirs here: http://androidxref.com/5.1.1_r6/xref/frameworks/base/core/java/android/app/ContextImpl.java#1039
The value is obtained from Environment.buildExternalStorageAppFilesDirs. Look at that source here: http://androidxref.com/5.1.1_r6/xref/frameworks/base/core/java/android/os/Environment.java#206
The value is dependent on mExternalDirsForApp, which in turn is populated by reading the contents of SECONDARY_STORAGE variable: http://androidxref.com/5.1.1_r6/xref/frameworks/base/core/java/android/os/Environment.java#136
As you can see, if the SECONDARY_STORAGE variable is not set, the sdcard path will not be returned. You can cross-check this by going to adb shell and looking at the output of echo $SECONDARY_STORAGE

use getExternalFilesDir()
It returns the path to files folder inside Android/data/data/your_package/ on your secondary storage SD card. It is used to store any required files for your app (e.g. images downloaded from web or cache files). Once the app is uninstalled, any data stored in this folder is gone too.
This is where you can write file in secondary storage ie(your micro sdcard)
if you want to write outside or the root of the secondary storage you have to use Storage access framework .

Accessing external mounted storage to write files. giving permission denied . I granted the write external storage

I am creating a FileManager app, where i am creating copy and cut functionality its working fine in internal device storage but when i try to copy something in external storage it says Permission denied. I have all the write permissions granted.
How can i write in external storage?

It depends what you mean by external storage. If you mean the external storage on the internal SD card, then
<uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE" />
<uses-permission android:name="android.permission.READ_EXTERNAL_STORAGE" />
in the manifest should be sufficient, assuming it is also granted in the App's security settings for Marshmallow and later.
On the other hand, if you mean an external removable SD card, then you will almost certainly not be able to write to it on KitKat or later unless you have taken specific steps to make it writeable.
There is a good summary of the state of play with removable SD cards here, which I suggest you take a look at:
How does storage access change on Android 6.

Android Accessing get external directory

Now, I am working on data transmission using bluetooth. I have such problem in selecting file in SD card/ internal storage.
I am already put permission in manifest :
I am using this command to get access the file
File sdCard = Environment.getExternalStorageDirectory();
But when I am check using this command if (sdCard.canRead()) , it can't read the path.
Anyone have the solution within my problem? Thanks anyway

The Android Dev resources has a good guide on this.
Assuming you have all the correct permissions, you could be facing issues where the storage is not mounted or there is not enough space. The guide explains how to check the state of the External Storage Dir, etc.

Did you add the following line to the AndroidManifest?
<uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE" />
From android SDK version 4, you need to add that line to access external storage by your app.
Some of other issues are, (Check whether phone detects the SD card)
SD Card is Not Clean
Battery Voltage
Card Slot is Squeezed
Metal Wires in the Card Slot Get Rusty and Twisted
Malware Invade SD Card
SD Card is not Formatted Properly
SD Card is Broken
The Phone Breakdown

problem solved.
The problem is related with new android SDK. We need to add additional permission.
Thanks everyone.