RecyclerView corrupts view using notifyItemMoved()

问题:

I'm having a problem with using the notifyItemMoved() method. It seems to be incorrectly displaying unmoved views.

My list has 4 element in it. What I want to do is animate a swap between item 1 and item 3. Items 1 and 3 swap correctly, but item 2 displays what was at item 3!

So the list starts off looking something like this:

Item 0 Item 1 Item 2 Item 3 

And ends like this:

Item 0 Item 3 Item 3 <!-- What the heck has this changed for? Item 1 

My adapter is backed by a List mProductList. I call the following code:

public void sortBackingListUsingSortingList(List<ProductWrapper> newProductItems) {     Log.e("", "Before:");     for(ProductWrapper wrapper : mProductItems) wrapper.log();     for(int i = 0; i < newProductItems.size(); i++) {         ProductWrapper currentItem   = mProductItems.get(i);         ProductWrapper correctItem   = newProductItems.get(i);          if(!currentItem.equals(correctItem)) {             // Item in wrong place             int indexOfCorrectItem = getIndexOfItemInList(mProductItems, correctItem);             Collections.swap(mProductItems, i, indexOfCorrectItem);             notifyItemMoved(i, indexOfCorrectItem);             Log.e("", "notifyItemMoved(" + i + ", " + indexOfCorrectItem+")");             Log.e("", "After:");             for(ProductWrapper wrapper : mProductItems) wrapper.log();         }     } } 

I've also added logging to onBindViewHolder to check if my view logic is being called:

@Override public void onBindViewHolder(HolderBasic holder, int position) {     Log.e("", "onBindViewHolder(holder, " + position + ")");     holder.fill(mProductItems.get(position)); } 

My logs look like this:

09-02 14:39:17.853  ： Before: 09-02 14:39:17.853  : Item 0 09-02 14:39:17.853  : Item 1 09-02 14:39:17.853  : Item 2 09-02 14:39:17.853  : Item 3  09-02 14:39:17.854  ： notifyItemMoved(1, 3)  09-02 14:39:17.854  ： After: 09-02 14:39:17.854  : Item 0 09-02 14:39:17.854  : Item 3 09-02 14:39:17.854  : Item 2 09-02 14:39:17.854  : Item 1  09-02 14:39:17.867  ： onBindViewHolder(holder, 1) 09-02 14:39:17.874  ： onBindViewHolder(holder, 3) 

As you can see, no reason for Item 2 to have change it's display at all - and yet, it does. Anybody know why?

EDIT

I can get around above by looping through the entire adapter and calling notifyItemChanged() on every item. Inefficient and not a good solution, but is invisible to the user.

回答1:

Thank you to @david.mihola for leading me to what I'm doing wrong.

This took so long to figure out as the symptom didn't make the problem obvious!

I was doing this:

Collections.swap(mProductItems, i, indexOfCorrectItem); notifyItemMoved(i, indexOfCorrectItem) 

But, I obviously didn't think through what notifyItemMoved() was actually doing. It is only notifying the adapter that item i has moved to indexOfCorrectItem it isn't telling the adapter that indexOfCorrectItem has also moved to i.

Under the covers it was doing the following:

1. Move item 1 to 3
2. Move what was at 2 to 1 to fill the gap
3. Move what was at 3 to 2 to fill the gap
4. notifyItemChanged(1);
5. notifyItemChanged(3);

The above of course leaves item 3 moved down to item 2 without a refreshed view! It was steps 4 and 5 which were hiding the problem by making item1 and item3 display correctly and leaving item2 incorrect!

As soon as I realised this I tried the following code:

notifyItemMoved(indexOfCorrectItem, i); notifyItemMoved(i, indexOfCorrectItem); 

This left the list in the correct order, but it short circuited the animation.

So, instead, I dumped swapping altogether:

mProductItems.remove(indexOfCorrectItem); mProductItems.add(i, correctItem); notifyItemMoved(indexOfCorrectItem, i); 

回答2:

I had the same issue. RecyclerView-Items are corrupt on drag&drop. But I have found a simple solution: In your RecyclerView.Adapter.class be sure to have the following

@Override public long getItemId(int position) {     // here code for getting the right itemID,      // i.e. return super.getItemId(mPosition);     // where mPosition ist the Position in the Collection. } 

You must return the right itemID for the position. From now on the Items are not corrupt.

回答3:

To get the actual position of your item after a drag&drop, add this method to your adapter:

private int getItemPosition(Item item){ // (<-- replace with your item)     int i = 0;     // (replace with your items and methods here)     for (Item currentItem : mItems) {         if (currentItem.getItemId() == item.getItemId()) break;         i++;     }     return i; } 

and call this instead of the position given by the viewHolder.

回答4:

Well, I handled it in a slightly different way, might help others.

        Collections.swap(mItemList, fromPosition, toPosition);         // Need to do below, because NotifyItemMove only handle one sided move         Item fromItem = mItemList.get(fromPosition);         Item toItem = mItemList.get(toPosition);         notifyItemChanged(fromPosition, toItem);         notifyItemChanged(toPosition, fromItem); 

I had to reorder items on a grid, and save the positions to a file. @Graeme was right, but i didn't wanted to give up on swapping. So just like @saganaut i sticked to notifyItemChanged. But only using notifyItemChanged sometimes left both swapped items on my grid with same items, so I binded the items with notifyItemChanged. It is not killing the animation, and is working as expected.

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