GalleryActivity.kt

class GalleryActivity : AppCompatActivity() {

    private val PICK_IMAGE_REQUEST = 71
    private var filePath: Uri? = null
    private var firebaseStore: FirebaseStorage? = null
    private var storageReference: StorageReference? = null

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_gallery)
        setSupportActionBar(toolbar)
        supportActionBar?.setDisplayHomeAsUpEnabled(true)

        firebaseStore = FirebaseStorage.getInstance()
        storageReference = FirebaseStorage.getInstance().reference

        btn_choose_image.setOnClickListener { launchGallery() }
        btn_upload_image.setOnClickListener { uploadImage() }
    }

    private fun launchGallery() {
        val intent = Intent()
        intent.type = "image/*"
        intent.action = Intent.ACTION_GET_CONTENT
        startActivityForResult(Intent.createChooser(intent, "Select Picture"), PICK_IMAGE_REQUEST)
    }
    
    override fun onActivityResult(requestCode: Int, resultCode: Int, data: Intent?) {
        super.onActivityResult(requestCode, resultCode, data)
        if (requestCode == PICK_IMAGE_REQUEST && resultCode == Activity.RESULT_OK) {
            if(data == null || data.data == null){
                return
            }

            filePath = data.data
            try {
                val bitmap = MediaStore.Images.Media.getBitmap(contentResolver, filePath)
                uploadImage.setImageBitmap(bitmap)
            } catch (e: IOException) {
                e.printStackTrace()
            }
        }
    }
    
    private fun addUploadRecordToDb(uri: String){
        val db = FirebaseFirestore.getInstance()

        val data = HashMap<String, Any>()
        data["imageUrl"] = uri

        db.collection("posts")
            .add(data)
            .addOnSuccessListener { documentReference ->
                Toast.makeText(this, "Saved to DB", Toast.LENGTH_LONG).show()
            }
            .addOnFailureListener { e ->
                Toast.makeText(this, "Error saving to DB", Toast.LENGTH_LONG).show()
            }
    }
    
    private fun uploadImage(){
        if(filePath != null){
            val ref = storageReference?.child("uploads/" + UUID.randomUUID().toString())
            val uploadTask = ref?.putFile(filePath!!)

            val urlTask = uploadTask?.continueWithTask(Continuation<UploadTask.TaskSnapshot, Task<Uri>> { task ->
                if (!task.isSuccessful) {
                    task.exception?.let {
                        throw it
                    }
                }
                return@Continuation ref.downloadUrl
            })?.addOnCompleteListener { task ->
                if (task.isSuccessful) {
                    val downloadUri = task.result
                    addUploadRecordToDb(downloadUri.toString())
                } else {
                    // Handle failures
                }
            }?.addOnFailureListener{

            }
        }else{
            Toast.makeText(this, "Please Upload an Image", Toast.LENGTH_SHORT).show()
        }
    }

}