kotlin: How to read a Uri in Android?

Question

I've been stuck with this for almost a week. Triend almost any answer/tutorial I found, but no luck yet.

I have an app that uses the camera. After the user takes a pic, and select the check/OK button in the camera, the camera returns, among other things, the Uri where the image was stored. It cames in the form of: content://media/external/images/media/122 (this is an actual pic in the phone), if I ask for the Uri.path I'll get in this case: /external/images/media/123

Now, with the Uri object, I can assign it to an imageView like imageView.setImageURI() and it works, so I'm pretty confident the images are stored somewhere.

Now, next thing my app should do, is take all the pictures taken, and send them to an API.

My problem is, when I try to read the Uri with any method, it gives me a FileNotFound Exception, no matter if I use the Uri or the path.

So I really don't know what to do. What am I missing? Do I have to explicitly save the image in a working directory? If so, how is it done? If not, how do I get the full path name including the filename? When I look at the DCIM directoy in the phone, I don't find the pics.

Thanks in advance!

EDIT

Code to take the pic:

    btnTomarFoto.setOnClickListener {
      if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.M) {
        if (checkSelfPermission(android.Manifest.permission.CAMERA) ==
          PackageManager.PERMISSION_DENIED || ContextCompat.checkSelfPermission(
            this,
            android.Manifest.permission.READ_EXTERNAL_STORAGE
          ) == PackageManager.PERMISSION_DENIED
        ) {
          // El permiso no fue concedido
          val permission = arrayOf(android.Manifest.permission.CAMERA,
                                    android.Manifest.permission.WRITE_EXTERNAL_STORAGE)
          requestPermissions(permission, PERMISSION_CODE)
        } else {
          // El permiso ya estaba concedido
          openCamera()
        }
      } else {
        // El SO es menor que Marshmallow
      }
    }
  }

Code to open the camera:

  private fun openCamera() {
    val values = ContentValues()
    values.put(MediaStore.Images.Media.TITLE, "New Picture")
    values.put(MediaStore.Images.Media.DESCRIPTION, "From the camera")
    image_uri = contentResolver.insert(MediaStore.Images.Media.EXTERNAL_CONTENT_URI, values)

    val cameraIntent = Intent(MediaStore.ACTION_IMAGE_CAPTURE)
    cameraIntent.putExtra(MediaStore.EXTRA_OUTPUT, image_uri)
    startActivityForResult(cameraIntent, IMAGE_CAPTURE_CODE)
  }

Code to store the Uri into the database:

  private fun guardarFoto() {
    var foto = FotografiaModel(actividad_id!!, image_uri.toString(), txtObservacion.text.toString())
    Log.w(tag, "URI: $image_uri PATH: " + image_uri!!.path + " Encoded Path: " + image_uri!!.encodedPath)
    fotografiaDBHelper.insertFoto(foto)
    visitaDBHelper.actualizaEstado(actividad_id!!, "INICIADO")
  }

There are some more things the code does, but this is the main thing. To show the received Uri into an Imageview I use:

  override fun onActivityResult(requestCode: Int, resultCode: Int, data: Intent?) {
    super.onActivityResult(requestCode, resultCode, data)
    if (resultCode == Activity.RESULT_OK) {
      imageView.setImageURI(image_uri)
      Log.v(tag, "Image URI: $image_uri")
    }
  }

Answer 1

My problem is, when I try to read the Uri with any method, it gives me a FileNotFound Exception, no matter if I use the Uri or the path.

That is because it is not a file. It is a Uri.

For example, https://stackoverflow.com/questions/56839478/kotlin-how-to-read-a-uri-in-android is a Uri. Your code assumes that the path /questions/56839478/kotlin-how-to-read-a-uri-in-android is the only thing that matters in a Uri. By your argument, every single computer on the planet (plus those in orbit) have a file located at /questions/56839478/kotlin-how-to-read-a-uri-in-android. That is not how a Uri works. You need to use the entire Uri to determine how to use it. In this case, https as a scheme means that you use HTTPS as a protocol to talk to the designated server (stackoverflow.com) to retrieve the content.

Similarly, the content scheme in your Uri from insert() indicates that you use ContentResolver to work with it. In particular, you can use openInputStream() to get an InputStream on the content identified by the Uri, just as you might use HttpUrlConnection or OkHttp to get an InputStream on an https Uri.

In particular, since you delegated data storage to some other app (the MediaStore), where the image is stored is up to somebody else, and it is not necessarily on the filesystem in a place where you can access it. That is particularly true on Android Q and higher, where you have limited access to arbitrary locations on the device via filesystem APIs.

Now, next thing my app should do, is take all the pictures taken, and send them to an API.

I am going to guess that "send them to an API" means "upload them to a server" (versus "call an API exposed by a library on the device" or "call a method in the Android SDK"). In that case, you have some code for talking to that server. It might be general-purpose code (e.g., OkHttp, Retrofit) or API-specific code (e.g., Facebook SDK).

Regardless, you will need to see what that code supports for your image content:

• If it supports a Uri, try using your Uri

• If it supports InputStream (or a Reader of some type), use openInputStream() on a ContentResolver

• If it supports a FileDescriptor or AssetFileDescriptor, use openFileDescriptor() on a ContentResolver

• If it only supports File, instead of using contentResolver.insert() to get the Uri to send to the camera app, use FileProvider, so you can have the images saved in a file that you control (e.g., in getCacheDir())

• Etc.