I desire to access media files from C code in android application.

I use this method to get file path by file uri:

fun getFileNameThatICanUseInNativeCode(uri: Uri?, applicationContext: Context): String? {
    val  mParcelFileDescriptor =
        applicationContext.contentResolver.openFileDescriptor(uri!!, "r")
    if (mParcelFileDescriptor != null) {
        val fd: Int = mParcelFileDescriptor.fd
        val file = File("/proc/self/fd/$fd")
        var path: String? = null
        try {
            path = Os.readlink(file.absolutePath).toString()
            mParcelFileDescriptor.close()
        } catch (e: ErrnoException) {
            e.printStackTrace()
        }

        return path
    } else {
        return null
    }
}

This method return generally this path, which could be accessed from C code

/mnt/user/0/emulated/0/DCIM/Camera/{fileName}

but for some phones it seems that the user folder is not found (maybe persmission issue, because the user folder is not acceable from adb shell (for example).

From adb shell, my file is also located here : /storage/emulated/0/DCIM/Camera/$fileName, this native_file_path also does not work

How to access this file from C code? For some phones i can access for others no:

  if((file = fopen(native_file_path,"a"))!=NULL)

I desire to access media files from C code in android application.

I use this method to get file path by file uri:

fun getFileNameThatICanUseInNativeCode(uri: Uri?, applicationContext: Context): String? {
    val  mParcelFileDescriptor =
        applicationContext.contentResolver.openFileDescriptor(uri!!, "r")
    if (mParcelFileDescriptor != null) {
        val fd: Int = mParcelFileDescriptor.fd
        val file = File("/proc/self/fd/$fd")
        var path: String? = null
        try {
            path = Os.readlink(file.absolutePath).toString()
            mParcelFileDescriptor.close()
        } catch (e: ErrnoException) {
            e.printStackTrace()
        }

        return path
    } else {
        return null
    }
}

This method return generally this path, which could be accessed from C code

/mnt/user/0/emulated/0/DCIM/Camera/{fileName}

but for some phones it seems that the user folder is not found (maybe persmission issue, because the user folder is not acceable from adb shell (for example).

From adb shell, my file is also located here : /storage/emulated/0/DCIM/Camera/$fileName, this native_file_path also does not work

How to access this file from C code? For some phones i can access for others no:

  if((file = fopen(native_file_path,"a"))!=NULL)

• android

• As the name might suggest, emulated/0 is not a native path, but it's emulated ...calling to Java through JNI might be an alternative: stackoverflow/a/29695982/549372 ...while the difference is single vs. multi-user filesystem layout. – Martin Zeitler Commented Nov 20, 2024 at 12:14
• Your method returns storage/emulated/0. My method returns /storage/emulated/0/DCIM/Camera/ where the video is located. But fopen does not see it. Could you prompt why? I am checking on real device. – Артемий Величко Commented Nov 20, 2024 at 13:34

1 Answer 1

Android 13 and higher:

<uses-permission android:name="android.permission.READ_MEDIA_IMAGES" />

The code I used:

class ImageInDcim(private val context: Context) {

    fun listImagesInDCIM() {
        if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.TIRAMISU) {
            if (ContextCompat.checkSelfPermission(context, Manifest.permission.READ_MEDIA_IMAGES) != PackageManager.PERMISSION_GRANTED) {
                ActivityCompat.requestPermissions(activity, arrayOf(Manifest.permission.READ_MEDIA_IMAGES), 100)
                return
            }
        } else if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.Q) {
            if (ContextCompat.checkSelfPermission(context, Manifest.permission.READ_EXTERNAL_STORAGE) != PackageManager.PERMISSION_GRANTED) {
                ActivityCompat.requestPermissions(activity, arrayOf(Manifest.permission.READ_EXTERNAL_STORAGE), 100)
                return
            }
        }
        
        val uri: Uri = MediaStore.Images.Media.EXTERNAL_CONTENT_URI
        val projection = arrayOf(
            MediaStore.Images.Media._ID,
            MediaStore.Images.Media.DISPLAY_NAME,
            MediaStore.Images.Media.DATA
        )
        
        val selection = "${MediaStore.Images.Media.DATA} LIKE ?"
        val selectionArgs = arrayOf("%/DCIM/%")

        val cursor = context.contentResolver.query(
            uri,
            projection,
            selection,
            selectionArgs,
            "${MediaStore.Images.Media.DATE_ADDED} DESC"
        )

        cursor?.use {
            val columnIndexDisplayName = it.getColumnIndex(MediaStore.Images.Media.DISPLAY_NAME)
            val columnIndexData = it.getColumnIndex(MediaStore.Images.Media.DATA)
            
            while (it.moveToNext()) {
                val displayName = it.getString(columnIndexDisplayName)
                val dataPath = it.getString(columnIndexData)

                println("Image found: $displayName at $dataPath")
            }
        }
    }
}