How to make alphabetical list on left in RecyclerView?

Question

Android

I want to implement such a thing (group name/image on the left)

But I can't figure out how.
All that comes to mind is to put one list into another, but this option is confusing.
Prompt the literature, or an example what.

Answer 1

After reading the RecyclerView documentation for a hundred rows, I came across such a thing RecyclerView.ItemDecoration With it, you can change the list item according to a certain condition. I searched for examples on this topic and came across this . Changed the drawVertical method like this:

public void drawVertical(Canvas c, RecyclerView parent) {
        final int left = this.dpToPx(72);
        final int right = parent.getWidth() - this.dpToPx(16);

        String firstLetter = "";
        String previousFirstLetter = "";
        TextView studentName;
        TextView nextStudentName;
        String nextFirstLetter = "";

        TextView groupMarkerText;

        final int childCount = parent.getChildCount();
        for (int i = 0; i < childCount; i++) {
            final View child = parent.getChildAt(i);
            final View nextChild = parent.getChildAt(i + 1);

            studentName = (TextView) child.findViewById(R.id.studentName);
            groupMarkerText = (TextView) child.findViewById(R.id.groupMarkerText);
            if (nextChild != null) {
                nextStudentName = (TextView) nextChild.findViewById(R.id.studentName);
                nextFirstLetter = (String) nextStudentName.getText().subSequence(0,1);
            }

            firstLetter = (String) studentName.getText().subSequence(0, 1);

            if (!firstLetter.equals(previousFirstLetter)) {
                groupMarkerText.setText(firstLetter);
                groupMarkerText.setVisibility(View.VISIBLE);
            }

            if (!nextFirstLetter.equals(firstLetter)) {
                final RecyclerView.LayoutParams params = (RecyclerView.LayoutParams) child
                        .getLayoutParams();
                final int top = child.getBottom() + params.bottomMargin;
                final int bottom = top + mDivider.getIntrinsicHeight();
                mDivider.setBounds(left, top, right, bottom);
                mDivider.draw(c);
            }

            previousFirstLetter = firstLetter;
        }

and here's what I got in the end:
What I wrote is nonsense, in fact, this approach is not suitable for RecyclerView due to its features. So parent.getChildCount(); will show the number of only visible lines, and while loading new ones, the drawVertical method will be called constantly. As a result, all new lines will be labeled.
Well, now I know where to dig.

Answer 2

This and This will help you