它需要运行时权限。如果授予了权限，则below checkpermission（）方法返回true，否则请求权限。用户是否授予了权限，将进入onrequestpermissionsresult（）。

fun checkPermission(decider: Int): Boolean {

    if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.M) {
        if (checkSelfPermission(Manifest.permission.WRITE_EXTERNAL_STORAGE) != 
   PackageManager.PERMISSION_GRANTED
            ) != PackageManager.PERMISSION_GRANTED || checkSelfPermission(
                Manifest.permission.READ_EXTERNAL_STORAGE
            ) != PackageManager.PERMISSION_GRANTED
        ) {
            ActivityCompat.requestPermissions(
                this,
                arrayOf(
                    Manifest.permission.WRITE_EXTERNAL_STORAGE,
                    Manifest.permission.READ_EXTERNAL_STORAGE
                ),
                Constants.checkPermission.REQUESTPERMISSION
            )
            return false
        } else {
            return true
        }
    } else {
        return true
    }
}

override fun onRequestPermissionsResult(
    requestCode: Int,
    permissions: Array<out String>,
    grantResults: IntArray
) {
    super.onRequestPermissionsResult(requestCode, permissions, grantResults)
    when (requestCode) {
        Constants.checkPermission.REQUESTPERMISSION -> {
            val writeExternalFile = grantResults[0] == 
PackageManager.PERMISSION_GRANTED
            val readExternalFile = grantResults[0] == 
PackageManager.PERMISSION_GRANTED

            if (readExternalFile && writeExternalFile) {
                Log.e("mesg", "permission granted")

            } else {
                Log.e("msg", "forceFullPermission")
            }
        }
    }
}