如何从android设备获取文件?

我有一个服务器,我应该在其中下载一个BASE64格式的文件(不要问我为什么有这个)。现在我正在上传一个pdf文件。目前,我正在尝试从设备获取文件路径,并将其解析为base64。它可以工作,但当我试图从非设备(例如,Google Photo)获取文件时,它不起作用。最好的方法是什么?

@SuppressLint("NewApi")
@Throws(URISyntaxException::class)
fun getFilePath(context: Context, uri: Uri): String? {
    var uri = uri
    var selection: String? = null
    var selectionArgs: Array<String>? = null
    // Uri is different in versions after KITKAT (Android 4.4), we need to
    if (Build.VERSION.SDK_INT < 28 && DocumentsContract.isDocumentUri(context.applicationContext, uri)) {
        if (isExternalStorageDocument(uri)) {
            val docId = DocumentsContract.getDocumentId(uri)
            val split =
                docId.split(":".toRegex()).dropLastWhile({ it.isEmpty() }).toTypedArray()
            return Environment.getExternalStorageDirectory().path + "/" + split[1]
        } else if (isDownloadsDocument(uri)) {
            val id = DocumentsContract.getDocumentId(uri)
            uri = ContentUris.withAppendedId(
                Uri.parse("content://downloads/public_downloads"),
                java.lang.Long.valueOf(id)
            )
        } else if (isMediaDocument(uri)) {
            val docId = DocumentsContract.getDocumentId(uri)
            val split =
                docId.split(":".toRegex()).dropLastWhile({ it.isEmpty() }).toTypedArray()
            val type = split[0]
            if ("image" == type) {
                uri = MediaStore.Images.Media.EXTERNAL_CONTENT_URI
            } else if ("video" == type) {
                uri = MediaStore.Video.Media.EXTERNAL_CONTENT_URI
            } else if ("audio" == type) {
                uri = MediaStore.Audio.Media.EXTERNAL_CONTENT_URI
            }
            selection = "_id=?"
            selectionArgs = arrayOf(split[1])
        } else if (isGooglePhotosUri(uri)) {

        }
    } else if (Build.VERSION.SDK_INT >= 28) {
        return uri.path.split(":")[1]
    }
    if ("content".equals(uri.getScheme(), ignoreCase = true)) {
        val projection = arrayOf<String>(MediaStore.Images.Media.DATA)
        var cursor: Cursor? = null
        try {
            cursor = context.contentResolver
                .query(uri, projection, selection, selectionArgs, null)
            val column_index = cursor!!.getColumnIndexOrThrow(MediaStore.Images.Media.DATA)
            if (cursor!!.moveToFirst()) {
                return cursor!!.getString(column_index)
            }
        } catch (e: Exception) {
            e.printStackTrace()
        }

    } else if ("file".equals(uri.getScheme(), ignoreCase = true)) {
        return uri.getPath()
    }
    return null
}

fun isExternalStorageDocument(uri: Uri): Boolean {
    return "com.android.externalstorage.documents" == uri.getAuthority()
}

fun isDownloadsDocument(uri: Uri): Boolean {
    return "com.android.providers.downloads.documents" == uri.getAuthority()
}

fun isMediaDocument(uri: Uri): Boolean {
    return "com.android.providers.media.documents" == uri.getAuthority()
}

fun isGooglePhotosUri(uri: Uri): Boolean {
    return uri.authority.contains("com.google.android.apps")
}