Binding an ObservableCollection to a Collection View

[ramirez]

Hi,

is there any more extensive example of binding an observableCollection of a collectionView? I'm porting an app I had in SwiftBond to ReactiveKit. I'm trying using the way explained here in the documentation and also using some inspiration from the SwiftBond demo app but I can't seem to be able to figure it out. I either get:

malloc: *** error for object 0x7fa13512a718: incorrect checksum for freed object - object was probably modified after being freed.
*** set a breakpoint in malloc_error_break to debug

from the ReactiveUIKit extension, or

*** Terminating app due to uncaught exception 'NSInternalInconsistencyException', reason: 'Invalid update: invalid number of items in section 0. The number of items contained in an existing section after the update (29) must be equal to the number of items contained in that section before the update (29), plus or minus the number of items inserted or deleted from that section (29 inserted, 0 deleted) and plus or minus the number of items moved into or out of that section (0 moved in, 0 moved out).'

on the same code. Any ideas or hints?

Thx!

LEo

[srdanrasic]

Hi @ramirez, hmm, that sounds bad. Could you post the code related to ObservableCollection and a Collection View and how are using it?

[ramirez]

Hi,

my problem seems to be that I keep changing the contents of the collection I'm using, based on an observed value. I have a ViewModel that has:

var localPosts:ObservableCollection<[Post]> = ObservableCollection<[Post]>([])

and I observe a variable that triggers a repopulation of the collection (One suspect that I have is that I put that in Init. Maybe I should do that binding later):

init () {
selectedUser.observe { event in
            Account.listPosts()
                .observeNext {
                    value in
                    self.localPosts.removeAll()
                    self.localPosts.insertContentsOf(value, at: 0)
            }
        }
}

In my view I bind the observable collection to my collectionView:

func bindView() {
        viewModel.localPosts.bindTo(collectionView) { (indexPath, dataSource, tableView) -> UICollectionViewCell in
            let cell = self.collectionView.dequeueReusableCellWithReuseIdentifier(reuseIdentifier, forIndexPath: indexPath) as! PostCollectionCellView
            let post = dataSource[indexPath.row]
            let cellViewModel = PostCollectionCellViewModel(post: post)
            cell.viewModel = cellViewModel
            post.updateFromBackend()
            return cell
            }.disposeIn(rBag)
    }

That's mostly it. The rest of the code is just layout.

The malloc error is reported in a line of
public class RKCollectionViewDataSource<C: ObservableCollectionType where C.Collection.Index == Int>: NSObject, UICollectionViewDataSource

in particular the init method:

public init(collection: C, collectionView: UICollectionView, animated: Bool = true, proxyDataSource: RKCollectionViewProxyDataSource?, createCell: (NSIndexPath, C.Collection, UICollectionView) -> UICollectionViewCell)

when calling: `uSelf.collectionView.performBatchUpdates``

Could it be that I'm modifying the collection before doing the binding to the collectionView a problem?
Cheers,

LEo

[srdanrasic]

Hmm, we might have a bug in the binding...

What happens if you replace

self.localPosts.removeAll()
self.localPosts.insertContentsOf(value, at: 0)

with

self.localPosts.replace(value)

That basically does the same thing, just in one line.

I'll try to reproduce modifying the collection before doing the binding - but that should also work.

[ramirez]

I tried but I get the same. The only way I found to make it work is by doing the binding before ever touching the collection.

[srdanrasic]

Hi @ramirez, I've traced the issue to table/collection view binding. Just released ReactiveUIKit 1.0.9 with the issue fixed. Please confirm if it works. Thanks!

[ramirez]

Works. Thx!

LEo

[retsohuang]

I use ReactiveUIKit 1.0.9 unfortunately it crashes after I update the data
Here's log

*** Terminating app due to uncaught exception 'NSInternalInconsistencyException', reason: 'attempt to insert item 8 into section 0, but there are only 8 items in section 0 after the update'

And I use the same function self.localPosts.replace(value)

[srdanrasic]

Looks like I have to spend some more time on this :) @retsohuang is it collection or table view?

[retsohuang]

That issue appears both CollectionView and TableView.

[srdanrasic]

Hi @retsohuang, could you provide some more context around the issues? I'm having hard time reproducing this...

[retsohuang]

I'll try to create demo project that reproduce this issue.

[AnthonyMDev]

This looks like its related to ReactiveKit/ReactiveUIKit#3.

Try removing the skip(1) as is described in that issues and see if that fixes the issue like it did for me.

[AnthonyMDev]

I'm 99% sure that this is fixed by ReactiveKit/ReactiveUIKit#5. I'd love to get this pulled in ASAP @srdanrasic
Thanks!