RecyclerView - Scroll To Position Not Working Every Time

问题

I have implemented a horizontal scrollable RecyclerView. My RecyclerView uses a LinearLayoutManager, and the problem I am facing is that when I try to use scrollToPosition(position) or smoothScrollToPosition(position) or from LinearLayoutManager's scrollToPositionWithOffset(position). Neither works for me. Either a scroll call doesn't scroll to the desired location or it doesn't invoke the OnScrollListener.

So far I have tried so many different combinations of code that I cannot post them all here. Following is the one that works for me (But only partially):

public void smoothUserScrollTo(final int position) {

    if (position < 0 || position > getAdapter().getItemCount()) {
        Log.e(TAG, "An attempt to scroll out of adapter size has been stopped.");
        return;
    }

    if (getLayoutManager() == null) {
        Log.e(TAG, "Cannot scroll to position a LayoutManager is not set. " +
                "Call setLayoutManager with a non-null layout.");
        return;
    }

    if (getChildAdapterPosition(getCenterView()) == position) {
        return;
    }

    stopScroll();

    scrollToPosition(position);

    if (lastScrollPosition == position) {

        addOnLayoutChangeListener(new OnLayoutChangeListener() {
            @Override
            public void onLayoutChange(View v, int left, int top, int right, int bottom, int oldLeft, int oldTop, int oldRight, int oldBottom) {

                if (left == oldLeft && right == oldRight && top == oldTop && bottom == oldBottom) {
                    removeOnLayoutChangeListener(this);

                    updateViews();

                    // removing the following line causes a position - 3 effect.
                    scrollToView(getChildAt(0));
                }
            }
        });
    }

    lastScrollPosition = position;
}

@Override
public void scrollToPosition(int position) {
    if (position < 0 || position > getAdapter().getItemCount()) {
        Log.e(TAG, "An attempt to scroll out of adapter size has been stopped.");
        return;
    }

    if (getLayoutManager() == null) {
        Log.e(TAG, "Cannot scroll to position a LayoutManager is not set. " +
                "Call setLayoutManager with a non-null layout.");
        return;
    }

//      stopScroll();

        ((LinearLayoutManager) getLayoutManager()).scrollToPositionWithOffset(position, 0);
//        getLayoutManager().scrollToPosition(position);
    }

I opted for scrollToPositionWithOffset() because of this but the case perhaps is different as I use a LinearLayoutManager instead of GridLayoutManager. But the solution does work for me too, but as I said earlier only partially.

When the call to scroll is from 0th position to totalSize - 7 scroll works like a charm.
When scroll is from totalSize - 7 to totalSize - 3, First time I only scroll to 7th last item in the list. The second time however I can scroll fine
When scrolling from totalSize - 3 to totalSize, I start getting unexpected behavior.

If anyone has found a work around I'd Appreciate it. Here's the gist to my code of custom ReyclerView.

回答1:

I had the same issue some weeks ago, and found only a really bad solution to solve it. Had to use a postDelayed with 200-300ms.

new Handler().postDelayed(new Runnable() {
    @Override
    public void run() {
        yourList.scrollToPosition(position);
    }
}, 200);

If you found a better solution, please let me know! Good luck!

回答2:

Turns out I was having a similar issue until I utilized

myRecyclerview.scrollToPosition(objectlist.size()-1)

It would always stay at the top when only putting in the objectlist size. This was until i decided to set the size equal to a variable. Again, that didn't work. Then I assumed that perhaps it was handling an outofboundsexception without telling me. So I subtracted it by 1. Then it worked.

回答3:

You can use LinearSmoothScroller this worked every time in my case:

First create an instance of LinearSmoothScroller:

  LinearSmoothScroller smoothScroller=new LinearSmoothScroller(activity){
            @Override
            protected int getVerticalSnapPreference() {
                return LinearSmoothScroller.SNAP_TO_START;
            }
        };

And then when you want to scroll recycler view to any position do this:

smoothScroller.setTargetPosition(pos);  // pos on which item you want to scroll recycler view
recyclerView.getLayoutManager().startSmoothScroll(smoothScroller);

Done.

回答4:

None of the methods seems to be working for me. Only the below single line of code worked

((LinearLayoutManager)mRecyclerView.getLayoutManager()).scrollToPositionWithOffset(adapter.currentPosition(),200);

The second parameter refers to offset, which is actually the distance (in pixels) between the start edge of the item view and start edge of the RecyclerView. I have supplied it with a constant value to make the top items also visible.

Check for more reference over here

回答5:

The accepted answer will work, but it may also break. The main reason for this issue is that the recycler view may not be ready by the time you ask it to scroll. The best solution for the same is to wait for the recycler view to be ready and then scroll. Luckily android has provided one such option. Below solution is for Kotlin, you can try the java alternative for the same, it will work.

newsRecyclerView.post {
    layoutManager?.scrollToPosition(viewModel.selectedItemPosition)
}

The post runnable method is available for every View elements and will execute once the view is ready, hence ensuring the code is executed exactly when required.

回答6:

So the problem for me was that I had a RecyclerView in a NestedScrollView. Took me some time to figure out this was the problem. The solution for this is (Kotlin):

val childY = recycler_view.y + recycler_view.getChildAt(position).y
nested_scrollview.smoothScrollTo(0, childY.toInt())

Java (credits to Himagi https://stackoverflow.com/a/50367883/2917564)

float y = recyclerView.getY() + recyclerView.getChildAt(selectedPosition).getY();    
scrollView.smoothScrollTo(0, (int) y);

The trick is to scroll the nested scrollview to the Y instead of the RecyclerView. This works decently at Android 5.0 Samsung J5 and Huawei P30 pro with Android 9.

回答7:

I had the same issue while creating a cyclic/circular adapter, where I could only scroll downward but not upward considering the position initialises to 0. I first considered using Robert's approach, but it was too unreliable as the Handler only fired once, and if I was unlucky the position wouldn't get initialised in some cases.

To resolve this, I create an interval Observable that checks every XXX amount of time to see whether the initialisation succeeded and afterward disposes of it. This approach worked very reliably for my use case.

private fun initialisePositionToAllowBidirectionalScrolling(layoutManager: LinearLayoutManager, realItemCount: Int) {
        val compositeDisposable = CompositeDisposable() // Added here for clarity, make this into a private global variable and clear in onDetach()/onPause() in case auto-disposal wouldn't ever occur here
        val initPosition = realItemCount * 1000

        Observable.interval(INIT_DELAY_MS, TimeUnit.MILLISECONDS)
                .observeOn(AndroidSchedulers.mainThread())
                .subscribe ({
                    if (layoutManager.findFirstVisibleItemPosition() == 0) {
                        layoutManager.scrollToPositionWithOffset(initPosition, 0)

                        if (layoutManager.findFirstCompletelyVisibleItemPosition() == initPosition) {
                            Timber.d("Adapter initialised, setting position to $initPosition and disposing interval subscription!")
                            compositeDisposable.clear()
                        }
                    }
                }, {
                    Timber.e("Failed to initialise position!\n$it")
                    compositeDisposable.clear()
                }).let { compositeDisposable.add(it) }
    }

回答8:

Had the same issue. My problem was, that I refilled the view with data in an async task, after I tried to scroll. From onPostExecute ofc fixed this problem. A Delay fixed this issue too, because when the scroll executed, the list had already been refilled.

回答9:

I use below solution to make the selected item in recycler view visible after the recycler view is reloaded (orientation change, etc). It overrides LinearLayoutManager and uses onSaveInstanceState to save current recycler position. Then in onRestoreInstanceState the saved position is restored. Finaly, in onLayoutCompleted, scrollToPosition(mRecyclerPosition) is used to make the previously selected recycler position visible again, but as Robert Banyai stated, for it to work reliably a certain delay must be inserted. I guess it is needed to provide enough time for adapter to load the data before scrollToPosition is called.

private class MyLayoutManager extends LinearLayoutManager{
    private boolean isRestored;

    public MyLayoutManager(Context context) {
        super(context);
    }

    public MyLayoutManager(Context context, int orientation, boolean reverseLayout) {
        super(context, orientation, reverseLayout);
    }

    public MyLayoutManager(Context context, AttributeSet attrs, int defStyleAttr, int defStyleRes) {
        super(context, attrs, defStyleAttr, defStyleRes);
    }

    @Override
    public void onLayoutCompleted(RecyclerView.State state) {
        super.onLayoutCompleted(state);
        if(isRestored && mRecyclerPosition >-1) {
            Handler handler=new Handler();
            handler.postDelayed(new Runnable() {
                @Override
                public void run() {
                    MyLayoutManager.this.scrollToPosition(mRecyclerPosition);
                }
            },200);

        }
        isRestored=false;
    }

    @Override
    public Parcelable onSaveInstanceState() {
        Parcelable savedInstanceState = super.onSaveInstanceState();
        Bundle bundle=new Bundle();
        bundle.putParcelable("saved_state",savedInstanceState);
        bundle.putInt("position", mRecyclerPosition);
        return bundle;
    }

    @Override
    public void onRestoreInstanceState(Parcelable state) {
        Parcelable savedState = ((Bundle)state).getParcelable("saved_state");
        mRecyclerPosition = ((Bundle)state).getInt("position",-1);
        isRestored=true;
        super.onRestoreInstanceState(savedState);
    }
}

回答10:

If you use recyclerview in nestedScrollView you must scroll nestScrollview

nestedScrollview.smoothScrollTo(0,0)

来源：https://stackoverflow.com/questions/36426129/recyclerview-scroll-to-position-not-working-every-time

标签

android

android-recyclerview

linearlayoutmanager