RecyclerView - How highlight central visible item during scroll

Question

I need a RecyclerView like this:

It should does:

• show 7 items per time (DONE)

• center the RecyclerView on the central visible item (DONE)

• when I scroll to right/left, the central item will be "highlighted" (the button is selected > blue color) (need HELP)

• when I click on a button, it will be centered with a smooth scrool (need HELP)

I used SnapHelper class to center the RecyclerView on the central items (I retrieve the central visible item getting the nearest child to the screen center)

MY ADAPTER:

public class RvTrendsGraphAdapter extends RecyclerView.Adapter<RvTrendsGraphAdapter.ViewHolder> {

    private float deviceWidth;
    private float itemWidth;

    private List<RvTrendsGraphModel> models;
    private Context context;

    public RvTrendsGraphAdapter(Context context, List<RvTrendsGraphModel> models) {
        this.models = models;
        this.context = context;
    }

    private Context getContext() {
        return context;
    }

    public class ViewHolder extends RecyclerView.ViewHolder {
        @BindView(R.id.rv_trends_graph_layout) PercentRelativeLayout rootLayout;
        @BindView(R.id.rv_trends_graph_layout_superiore) PercentRelativeLayout layoutSuperiore;
        @BindView(R.id.rv_trends_graph_layout_inferiore) RelativeLayout layoutInferiore;
        @BindView(R.id.rv_trends_graph_vertical_progressbar) ProgressBar verticalProgressBar;
        @BindView(R.id.rv_trends_graph_button) Button timeLapseButton;

        public ViewHolder(View itemView) {
            super(itemView);
            ButterKnife.bind(this, itemView);
        }
    }


    @Override
    public RvTrendsGraphAdapter.ViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
        Context context = parent.getContext();
        LayoutInflater inflater = LayoutInflater.from(context);
        View view = inflater.inflate(R.layout.recycler_trends_graph, parent, false);

        // Set the width to show 7 elements
        DisplayMetrics displayMetrics = new DisplayMetrics();
        WindowManager windowmanager = (WindowManager) getContext().getSystemService(Context.WINDOW_SERVICE);
        windowmanager.getDefaultDisplay().getMetrics(displayMetrics);
        deviceWidth = displayMetrics.widthPixels;
        float progressBarWidth = getContext().getResources().getDimension(R.dimen.picker_time_lapse_progressbar_width);
        itemWidth = ((deviceWidth + progressBarWidth) / 8f + 1f);
        view.getLayoutParams().width = (int) itemWidth;

        return new ViewHolder(view);
    }

    @Override
    public void onBindViewHolder(RvTrendsGraphAdapter.ViewHolder viewHolder, int position) {
        RvTrendsGraphModel model = models.get(position);

        PercentRelativeLayout rootLayout = viewHolder.rootLayout;
        ProgressBar verticalProgressBar = viewHolder.verticalProgressBar;
        Button timeLapseButton = viewHolder.timeLapseButton;

        verticalProgressBar.setProgress(model.getProgress());
        setTimeLapseButton(timeLapseButton, model.getTimeLapseValue());
    }

    @Override
    public int getItemCount() {
        return models.size();
    }

    public RvTrendsGraphModel getItem(int position) {
        return models.get(position);
    }

    /* UTILS */

    private void setTimeLapseButton(Button button, String text) {
        //button.setSelected(false);
        button.setText(text);
    }

}

SETUP RECYCLER VIEW:

mLayoutManager = new LinearLayoutManager(getActivity(), LinearLayoutManager.HORIZONTAL, false);
mRecyclerView.setLayoutManager(mLayoutManager);

SnapHelper snapHelper = new LinearSnapHelper();
snapHelper.attachToRecyclerView(mRecyclerView);

POPULATE RECYCLER VIEW:

list = new ArrayList<>();
/* Create foo list... */
list.add(new RvTrendsGraphModel(75, String.valueOf(list.size())));
list.add(new RvTrendsGraphModel(33, String.valueOf(list.size())));
// ...

adapter = new RvTrendsGraphAdapter(getActivity(), list);
mRecyclerView.setAdapter(adapter);
adapter.notifyDataSetChanged();

mRecyclerView.smoothScrollToPosition(list.size() - 1);

SCROLL MANAGEMENT:

mRecyclerView.addOnScrollListener(new RecyclerView.OnScrollListener() {
            @Override
            public void onScrolled(RecyclerView recyclerView, int dx, int dy) {
                // Get adapter position of the central item
                PercentRelativeLayout root = (PercentRelativeLayout) mRecyclerView.findChildViewUnder(centralX, 0);
                pos = mRecyclerView.getChildAdapterPosition(root);

                // first try (very bad)
                if (lastPos != pos) {
                    pos = lastPos;
                    adapter.notifyDataSetChanged();
                }

                // second try (I cannot call notifyitemchanged during the scroll
                if () {
                    final int pos = mRecyclerView.getChildAdapterPosition(root);
                    adapter.getItem(pos).setCentered(true);
                    adapter.notifyItemChanged(pos);
                }
            }
        });

ITEM LAYOUT:

<?xml version="1.0" encoding="utf-8"?>
<android.support.percent.PercentRelativeLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:id="@+id/rv_trends_graph_layout"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:ignore="MissingPrefix">

    <android.support.percent.PercentRelativeLayout
        android:id="@+id/rv_trends_graph_layout_superiore"
        android:layout_width="match_parent"
        android:layout_height="0dp"
        app:layout_heightPercent="75%">

        <ProgressBar
            android:id="@+id/rv_trends_graph_vertical_progressbar"
            style="@style/Widget.ProgressBar.Vertical"
            android:layout_width="@dimen/picker_time_lapse_progressbar_width"
            android:layout_height="match_parent"
            android:layout_alignParentBottom="true"
            android:layout_centerHorizontal="true"
            android:progress="50"
            />
    </android.support.percent.PercentRelativeLayout>

    <RelativeLayout
        android:id="@+id/rv_trends_graph_layout_inferiore"
        android:layout_width="match_parent"
        android:layout_height="0dp"
        android:layout_below="@+id/rv_trends_graph_layout_superiore"
        app:layout_heightPercent="25%">

        <Button
            android:id="@+id/rv_trends_graph_button"
            fontPath="fonts/Roboto-Light.ttf"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_centerInParent="true"
            android:background="@drawable/picker_time_lapse_selector"
            android:minHeight="0dp"
            android:minWidth="0dp"
            android:textAllCaps="true"
            android:textColor="@color/picker_time_lapse_text_color_selector"
            android:textSize="@dimen/text_size_medium"
            tools:ignore="ContentDescription"
            tools:text="16"/>

    </RelativeLayout>

</android.support.percent.PercentRelativeLayout>

Answer 1

Hope this helps -

Note that this is a hacky solution, especially the highlighting on scroll. Also, I have not profiled any performance. You should probably check it. I also changed timeLapseButton to TextView since changing background on Button will collapse other layout properties.

If you don't like hacky solution, you could check out some chart libraries.

ex:) https://github.com/PhilJay/MPAndroidChart

Adapter class

public interface TimeLapseButtonClickListener {
    void onClick(int position);
}

private TimeLapseButtonClickListener timeLapseButtonListener;

public void setTimeLapseButtonClickListener(TimeLapseButtonClickListener listener) {
    this.timeLapseButtonListener = listener;
}

private void setTimeLapseButton(Button button, String text, final int position) {
    button.setText(text);

    button.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View view) {
            this.timeLapseButtonListener.onClick(position);
        }
    });
}

Activity or Fragment where you have recyclerView & adapter

...

private int prevCenterPos; // Keep track the previous pos to dehighlight

...

// Click and smooth scroll to get clicked item in the middle
adapter.setListener(new RvTrendsGraphAdapter.TimeLapseButtonClickListener() {
    @Override
    public void onClick(int position) {
        View view = mRecyclerView.getLayoutManager().findViewByPosition(position);
        int middle = mRecyclerView.getWidth() / 2;
        mRecyclerView.smoothScrollBy(view.getLeft() - middle, 0, new AccelerateDecelerateInterpolator());
    }
});

// Highlight view in the middle on scroll
mRecyclerView.addOnScrollListener(new RecyclerView.OnScrollListener() {

    @Override
    public void onScrolled(RecyclerView recyclerView, int dx, int dy) {
        super.onScrolled(recyclerView, dx, dy);

        int center = mRecyclerView.getWidth() / 2;
        View centerView = mRecyclerView.findChildViewUnder(center, mRecyclerView.getTop());
        int centerPos = mRecyclerView.getChildAdapterPosition(centerView);

        if (prevCenterPos != centerPos) {
            // dehighlight the previously highlighted view
            View prevView = mRecyclerView.getLayoutManager().findViewByPosition(prevCenterPos);
            if (prevView != null) {
                View button = prevView.findViewById(R.id.rv_trends_graph_button);
                int white = ContextCompat.getColor(context, R.color.white);
                button.setBackgroundColor(white);
            }

            // highlight view in the middle 
            if (centerView != null) {
                View button = centerView.findViewById(R.id.rv_trends_graph_button);
                int highlightColor = ContextCompat.getColor(context, R.color.colorAccent);
                button.setBackgroundColor(highlightColor);
            }

            prevCenterPos = centerPos;
        }
    }
});