在调用notifydatasetchanged后，Recyclerview滚动到顶部

Question

I have a horizontal recyclerview (with a LinearLayoutManager) and it's child item has an imageview wrapped in a relativelayout. The recyclerview has three horizontal rows that contain child items. When the recyclerview is scrolled, I'm updating the dataset with the response from an http call and calling notifydatasetChanged in the http response callback. If the recyclerview child item's height and width are fixed values (Eg. 150dp, 84dp) the recyclerview behaves as intended ie, loads the new items and stays at the same scroll position but if I set height and width of recyclerview's child item as match_parent and wrap_content, the recyclerview is completely refreshed and scrolls to the first position. Why is this happening? Note: I have checked other similar questions on SO and none of them offer a workable solution.

main_layout

<android.support.v7.widget.RecyclerView
    android:id="@+id/grid_recycler_view"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:layout_marginBottom="110dp"
    android:layout_marginLeft="15dp"
    android:layout_marginTop="80dp"
    android:background="@color/transparent"
    android:outlineProvider="bounds"
    android:elevation="8dp"
    android:padding="0dp"
    android:scrollbars="none" />
....

recycler_view_child_item

<RelativeLayout      xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical"
android:padding="0dp">
<ImageView
    android:id="@+id/thumbnail"
    android:layout_width="wrap_content"
    android:layout_height="match_parent"
    android:adjustViewBounds="true"
    android:maxWidth="126dp"
    android:maxHeight="225dp"
    android:padding="0dp"/>
</RelativeLayout>

Answer 1

I was having the same issue and could not find a solution on SO either. The issue was caused by not setting a LayoutManager for the RecyclerView . I know you say you have a LinearLayoutManager . But make sure you have it set up in the following way. (In my case, I'm using a HorizontalGridView , but the same principle applies for RecyclerView ).

horizontalGridView = (HorizontalGridView) findViewById(R.id.gridView);
GridElementAdapter adapter = newGridElementAdapter(VenueProfileActivity.this, mDeals);
horizontalGridView.setAdapter(adapter);

HorizontalGridView.LayoutManager layoutManager = new LinearLayoutManager(VenueProfileActivity.this, LinearLayoutManager.HORIZONTAL, false);
horizontalGridView.setLayoutManager(layoutManager);
horizontalGridView.setHasFixedSize(true);

Answer 2

The refresh probably happens because you have not specified the size of the child views. First thing I would do is remove the RelativeLayout which reduces the view depth since it doesn't seem to have any purpose. Also if the the child views of the recyclerView are always the same size set it on the childViews themselves instead of the parentView aka the recyclerView. Also did you setHasFixedSize to true on the recyclerView?

Answer 3

I had the same problem and found the answer from mossy321 useful but didn't fix everything for me. In my application I had a list of objects and each one had a time on it which needed to be incremented every 30 seconds or so. I ran one timer in the hosting Fragment but updating the data caused the jumping problem.

My recycler code is as follows:

 orderRecycler = (RecyclerView) rootView.findViewById(R.id.order_recycler_view);
    // use this setting to improve performance if you know that changes
    // in content do not change the layout size of the RecyclerView
    orderRecycler.setHasFixedSize(true);

    //Stops items doing a default flashing animation on individual refresh
    RecyclerView.ItemAnimator animator = orderRecycler.getItemAnimator();
    if (animator instanceof SimpleItemAnimator) {
        ((SimpleItemAnimator) animator).setSupportsChangeAnimations(false);
    }

    orderLayoutManager = new LinearLayoutManager(getActivity());
    orderRecycler.setLayoutManager(orderLayoutManager);
    orderAdapter = new OrderAdapter(orderArrayList, historyArrayList, getActivity());

    orderRecycler.setAdapter(orderAdapter);

Of note here is that the setHasFixedSize is critical. I would guess that on data change, the system has to redraw the views forcing the jump to the top problem, but if it knows they are going to be of the same size, it can just update the changed text in this case.

The other problem was that I could NOT use notifyDatasetChanged or it would still cause the same problem. I had to notify for each item individually. This is what the item animator is for in the recycler declaration. Without that, the items would flash on update.

 for(int i = 0; i < orderArrayList.size(); i++){
                orderAdapter.notifyItemChanged(i);
            }

Answer 4

当您调用notifyDataSetChanged时，可以将RecyclerView滚动到特定位置

recyclerView.scrollToPosition(array.size() - 1);