List not emitting on remove item (RxKotlin)

Question

I'm working on an Android App. I have a list of photos loaded in memory. I want to make use of Reactive library, so I declare a memory-base datasource where I save the list:

    @Singleton
    class MemoryPhotosSource @Inject constructor() {
         var photos: MutableList<Image> = mutableListOf()
         ...

         // Here is my function to add items to list.
         fun addPhoto(image: Image) {
              photos.add(image)
         }

         // Here is my function to list the items.
         fun listPhotos(): List<Image> = photos

         // Here is my function to remove items from list.
         fun removePhoto(image: Image): Image {
               photos.remove(image)
               return image
         }
    }

Then, I have a ViewModel where I call these methods:

class CreateDocumentFromPhotosViewModel @Inject constructor(): ViewModel() {
       @Inject
       lateinit var source: MemoryPhotosSource

       fun listImages(): Observable<List<Image>> = Observable.fromCallable {
           source.listPhotos()
       }.applySchedulers()

       fun addImage(image: Image) {
           source.addPhoto(image)
       }

       fun removeImage(image: Image): Image {
           source.removePhoto(image)
           return image
       }
}

Finally, I subscribe in my application:

    dis add viewModel.listImages()
            .subscribe {
                adapter.data = it
            }

    dis add onDelete
            .map { viewModel.removeImage(it) }
            .map { showSnackbar(parentView, resources.getString(R.string.document_removed), resources.getString(R.string.undo), it)}
            .map { it.subscribe { viewModel.addImage(it) } }
            .subscribe()

Listing and adding images work nicely. However, when I press the delete button, which publish in the onDelete subject, the snackbar is shown, but no change is performed to the RecyclerView adapter. Debugging, I noticed that the removePhoto function is being called in MemoryPhotosSource class, and the list is being successfuly modified. However, it does not emit the changes, that's why the RecyclerView is not updated. I confirmed this behavior by leaving the application and entering again, which forced the repainting of the Recycler, and then, the removed element didn't show up, as it should be. So, I think the problem is the list doesn't emit the changes when an item is removed.

Does anybody know a way to solve this? Any help would be much appreciated.

Thanks!

score 0 · Answer 1 · answered Jun 20 '18 at 14:00

0

You should use defer operator while creating your observable list. It returns refresh list when you subscribed.

answered Jun 20 '18 at 14:00

gokhan

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Hi, @gokhan, thanks for your answer. This means I would have to subscribe multiple times to the observer? – Sebastián Landínez García Jun 20 '18 at 14:07
@SebastiánLandínezGarcía Nope I mean wrap callable object with defer operator – gokhan Jun 20 '18 at 14:14
I'm quite new to Rx library. Does this mean I should do my listImages function equal to Observable.fromCallable {...}.defer? Or perform some compose operation? Thanks! – Sebastián Landínez García Jun 20 '18 at 14:28

List not emitting on remove item (RxKotlin)

1 Answers1