检测当前在RecyclerView中滚动到哪个项目

Question

I'm trying to implement an autoplay feature for video items in a RecyclerView (linear vertical layout). I can't figure out how to know when a certain item is currently on/off the screen so I can autoplay/pause the video. If I put the code in onBindViewHolder method all videos start playing simultaniously. Couldn't find a solution by googling it either. Help, please!

Answer 1

For Recyclerview you should rely on your layout manager to give you this information.

https://developer.android.com/reference/android/support/v7/widget/GridLayoutManager or https://developer.android.com/reference/android/support/v7/widget/LinearLayoutManager

Assign a layout to the RecyclerView when you assign the adapter. Then use it to see what is visible.

Let me help a bit more with some Psedo Kotlin code for you to help with the player aspect.

Let's pretend you have some object that is bound into each row that can trigger the playing and has a unique ID. Let's call that an ActiveRowPlayer for this example.

NOTE* If you are using databinding, it is simple to bind your video player playing content to a property in your model that is populating the row, but that's different story for a different post.

You can make an interface like:

interface IActivePlayerUpdater{
    fun onUpdateCurrentPlayer
}

You can make a helper method like:

in your activity, you can implement an interface like :IActivePlayerUpdater and override the methods for it.

override fun onUpdateCurrentPlayer(){
    var activeRowPlayer = recyclerView.layoutManager.findFirstCompletelyVisibleItemPosition()
    if(activeRowplayer.someID != currentRowPlayer.someID){
        currentRowPlayer.stopPlaying
        currentRowPlayer = activeRowPlayer
        activeRowPlayer.startPlaying
    }
}

Then pass it into your adapter and just monitor your onBind method and anytime a new onBind is called that means the content has moved enough to trigger a new row item.

MyAdapterConstructor(IActivePlayerUpdater myCallback)

fun recyclerView.onBindMethod(stuffThatComesHere){
    //do normal stuff
    myCallback.onUpdateCurrentPlayer()
}

Keep in mind, this is just pseudo to help you on your journey. not intended to be direct copy and paste.

----NOTE* REQUESTED FROM COMMENT TO SUPPLY HOW TO TOUCH VIEWMODEL FROM OUTSIDE OF ADAPTER---

@Goran, this example I had setup a long time ago to avoid notifyDataSetChanged on selection changed to toggle a checkbox for each item. I eventually moved to a better option, but you asked how do you get the viewmodel, here is a sample. rvCameraRoll was my recyclerView, I was using it to display camera media, but that is not relevant, just focus on getting the viewModel piece.

The only part you should care about is getting the ViewHolder, I just left the rest there in case it helps you with anything else.

     int count = rvCameraRoll.getChildCount();
    for (int i = 0; i < count; i++) {
        MediaModelGridAdapter.ViewHolder childRow = (MediaModelGridAdapter.ViewHolder)rvCameraRoll.getChildViewHolder(rvCameraRoll.getChildAt(i));
        if(isVisible) {
            childRow.imgCellSelected.setVisibility(View.VISIBLE);
            if(getMediaModelList().get(i).getIsSelected()){
                childRow.imgCellSelected.setBackgroundResource(R.drawable.ic_ap_selected_on);
            }

        }else{
            //check that exists, because after fresh delete list may be short while updating cells
            if(getMediaModelList().size() > i) {
                getMediaModelList().get(i).setIsSelected(false);
            }
            childRow.imgCellSelected.setBackgroundResource(R.drawable.ic_ap_selected_off);
            childRow.imgCellSelected.setVisibility(View.GONE);

        }

    }

OLD

leaving this for anyone using a ListView

There is a OnScrollListener for ListView

You can override the

onScrollStateChanged(AbsListView view, int scrollState)

and the

onScroll(AbsListView view, int firstVisibleItem, int visibleItemCount, int totalItemCount)

this will give you the ListView item that is visible. So by using the onScroll you can detect which items are visible and determine which one to play and stop playing.

if you use with recyclerview https://developer.android.com/reference/android/support/v7/widget/RecyclerView.OnScrollListener

Answer 2

The RecyclerView is only holding the items and the LayoutManager is responsible for displaying the items, so in order to get the ones that are visible to the user, assuming that you use LinearLayoutManager, you should call : ((LinearLayoutManager)recyclerView.getLayoutManager()).findFirstVisibleItemPosition(); or ((LinearLayoutManager)recyclerView.getLayoutManager()).findLastVisibleItemPosition();