Pinned groups in ExpandableListView

Question

Is there a standard way to pin group item to the top of screen while scrolling group's items. I saw similar examples with ListView. What interfaces should I implement or what methods override ?

Answer 1

I found solution based on Pinned Header ListView of Peter Kuterna and android sample ExpandableList1.java. PinnedHeaderExpListView.java

package com.example;

import com.example.ExpandableList.MyExpandableListAdapter;

import android.content.Context;
import android.graphics.Canvas;
import android.util.AttributeSet;
import android.view.View;
import android.widget.BaseExpandableListAdapter;
import android.widget.ExpandableListAdapter;
import android.widget.ExpandableListView;
import android.widget.TextView;

/**
 * A ListView that maintains a header pinned at the top of the list. The
 * pinned header can be pushed up and dissolved as needed.
 */
public class PinnedHeaderExpListView extends ExpandableListView{

    /**
     * Adapter interface.  The list adapter must implement this interface.
     */
    public interface PinnedHeaderAdapter {

        /**
         * Pinned header state: don't show the header.
         */
        public static final int PINNED_HEADER_GONE = 0;

        /**
         * Pinned header state: show the header at the top of the list.
         */
        public static final int PINNED_HEADER_VISIBLE = 1;

        /**
         * Pinned header state: show the header. If the header extends beyond
         * the bottom of the first shown element, push it up and clip.
         */
        public static final int PINNED_HEADER_PUSHED_UP = 2;

        /**
         * Configures the pinned header view to match the first visible list item.
         *
         * @param header pinned header view.
         * @param position position of the first visible list item.
         * @param alpha fading of the header view, between 0 and 255.
         */
        void configurePinnedHeader(View header, int position, int alpha);
    }

    private static final int MAX_ALPHA = 255;

    private MyExpandableListAdapter mAdapter;
    private View mHeaderView;
    private boolean mHeaderViewVisible;

    private int mHeaderViewWidth;

    private int mHeaderViewHeight;

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

    public PinnedHeaderExpListView(Context context, AttributeSet attrs) {
        super(context, attrs);
    }

    public PinnedHeaderExpListView(Context context, AttributeSet attrs, int defStyle) {
        super(context, attrs, defStyle);
    }

    public void setPinnedHeaderView(View view) {
        mHeaderView = view;

        // Disable vertical fading when the pinned header is present
        // TODO change ListView to allow separate measures for top and bottom fading edge;
        // in this particular case we would like to disable the top, but not the bottom edge.
        if (mHeaderView != null) {
            setFadingEdgeLength(0);
        }
        requestLayout();
    }

    @Override
    public void setAdapter(ExpandableListAdapter adapter) {
        super.setAdapter(adapter);
        mAdapter = (MyExpandableListAdapter)adapter;
    }

    @Override
    protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
        super.onMeasure(widthMeasureSpec, heightMeasureSpec);
        if (mHeaderView != null) {
            measureChild(mHeaderView, widthMeasureSpec, heightMeasureSpec);
            mHeaderViewWidth = mHeaderView.getMeasuredWidth();
            mHeaderViewHeight = mHeaderView.getMeasuredHeight();
        }
    }

    @Override
    protected void onLayout(boolean changed, int left, int top, int right, int bottom) {
        super.onLayout(changed, left, top, right, bottom);
        if (mHeaderView != null) {
            mHeaderView.layout(0, 0, mHeaderViewWidth, mHeaderViewHeight);
            configureHeaderView(getFirstVisiblePosition());
        }
    }

    /** 
     * animating header pushing
     * @param position
     */
    public void configureHeaderView(int position) {
        final int group = getPackedPositionGroup(getExpandableListPosition(position));
        int groupView = getFlatListPosition(getPackedPositionForGroup(group));

        if (mHeaderView == null) {
            return;
        }

        mHeaderView.setOnClickListener(new OnClickListener() {

            public void onClick(View header) {
                if(!expandGroup(group)) collapseGroup(group); 
            }
        }); 

        int state,nextSectionPosition = getFlatListPosition(getPackedPositionForGroup(group+1));

        if (mAdapter.getGroupCount()== 0) {
            state = PinnedHeaderAdapter.PINNED_HEADER_GONE;
        }else if (position < 0) {
            state = PinnedHeaderAdapter.PINNED_HEADER_GONE;
        }else if (nextSectionPosition != -1 && position == nextSectionPosition - 1) {
            state=PinnedHeaderAdapter.PINNED_HEADER_PUSHED_UP;
        }else  state=PinnedHeaderAdapter.PINNED_HEADER_VISIBLE;

        switch (state) {    
            case PinnedHeaderAdapter.PINNED_HEADER_GONE: {
                mHeaderViewVisible = false;
                break;
            }

            case PinnedHeaderAdapter.PINNED_HEADER_VISIBLE: {
                mAdapter.configurePinnedHeader(mHeaderView, group, MAX_ALPHA);
                if (mHeaderView.getTop() != 0) {
                    mHeaderView.layout(0, 0, mHeaderViewWidth, mHeaderViewHeight);
                }
                mHeaderViewVisible = true;
                break;
            }

            case PinnedHeaderAdapter.PINNED_HEADER_PUSHED_UP: {
                View firstView = getChildAt(0);
                if(firstView==null){
                    if (mHeaderView.getTop() != 0) {
                        mHeaderView.layout(0, 0, mHeaderViewWidth, mHeaderViewHeight);
                    }
                    mHeaderViewVisible = true;
                    break;
                }
                int bottom = firstView.getBottom();
                int itemHeight = firstView.getHeight();
                int headerHeight = mHeaderView.getHeight();
                int y;
                int alpha;
                if (bottom < headerHeight) {
                    y = (bottom - headerHeight);
                    alpha = MAX_ALPHA * (headerHeight + y) / headerHeight;
                } else {
                    y = 0;
                    alpha = MAX_ALPHA;
                }
                mAdapter.configurePinnedHeader(mHeaderView, group, alpha);
                //выползание
                if (mHeaderView.getTop() != y) {
                    mHeaderView.layout(0, y, mHeaderViewWidth, mHeaderViewHeight + y);
                }
                mHeaderViewVisible = true;
                break;
            }
        }
    }

    @Override
    protected void dispatchDraw(Canvas canvas) {
        super.dispatchDraw(canvas);
        if (mHeaderViewVisible) {
            drawChild(canvas, mHeaderView, getDrawingTime());
        }
    }

}

ExpandableList.java

package com.example;


import android.app.Activity;
import android.graphics.Color;
import android.os.Bundle;
import android.view.Gravity;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.AbsListView;
import android.widget.AbsListView.LayoutParams;
import android.widget.AbsListView.OnScrollListener;
import android.widget.AdapterView;
import android.widget.AdapterView.OnItemClickListener;
import android.widget.BaseExpandableListAdapter;
import android.widget.ExpandableListAdapter;
import android.widget.SectionIndexer;
import android.widget.TextView;
import android.widget.Toast;

import com.example.PinnedHeaderExpListView.PinnedHeaderAdapter;



/**
 * Demonstrates expandable lists using a custom {@link ExpandableListAdapter}
 * from {@link BaseExpandableListAdapter}.
 */
public class ExpandableList extends Activity {

    MyExpandableListAdapter mAdapter;
    PinnedHeaderExpListView elv;

    private int mPinnedHeaderBackgroundColor;
    private int mPinnedHeaderTextColor;

    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);

        // Set up our adapter
        mAdapter = new MyExpandableListAdapter();
        elv = (PinnedHeaderExpListView) findViewById(R.id.list);

        elv.setAdapter(mAdapter);

        mPinnedHeaderBackgroundColor = getResources().getColor(android.R.color.black);
        mPinnedHeaderTextColor = getResources().getColor(android.R.color.white);

        elv.setGroupIndicator(null);
        View h = LayoutInflater.from(this).inflate(R.layout.header, (ViewGroup) findViewById(R.id.root), false);
        elv.setPinnedHeaderView(h);
        elv.setOnScrollListener((OnScrollListener) mAdapter);
        elv.setDividerHeight(0);
    }

    /**
     * A simple adapter which maintains an ArrayList of photo resource Ids. 
     * Each photo is displayed as an image. This adapter supports clearing the
     * list of photos and adding a new photo.
     *
     */
    public class MyExpandableListAdapter extends BaseExpandableListAdapter implements PinnedHeaderAdapter, OnScrollListener{
        // Sample data set.  children[i] contains the children (String[]) for groups[i].
        private String[] groups = { "People Names", "Dog Names", "Cat Names", "Fish Names" };
        private String[][] children = {
                { "Arnold", "Barry", "Chuck", "David", "Stas", "Oleg", "Max","Alex","Romeo", "Adolf" },
                { "Ace", "Bandit", "Cha-Cha", "Deuce", "Nokki", "Baron", "Sharik", "Toshka","SObaka","Belka","Strelka","Zhuchka"},
                { "Fluffy", "Snuggles","Cate", "Yasha","Bars" },
                { "Goldy", "Bubbles","Fluffy", "Snuggles","Guffy", "Snoopy" }
        };

        public Object getChild(int groupPosition, int childPosition) {
            return children[groupPosition][childPosition];
        }

        public long getChildId(int groupPosition, int childPosition) {
            return childPosition;
        }

        public int getChildrenCount(int groupPosition) {
            return children[groupPosition].length;
        }

        public TextView getGenericView() {
            // Layout parameters for the ExpandableListView
            AbsListView.LayoutParams lp = new AbsListView.LayoutParams(
                    ViewGroup.LayoutParams.MATCH_PARENT, 64);

            TextView textView = new TextView(ExpandableList.this);
            textView.setLayoutParams(lp);
            // Center the text vertically
            textView.setGravity(Gravity.CENTER_VERTICAL | Gravity.LEFT);
            // Set the text starting position
            textView.setPadding(36, 0, 0, 0);
            return textView;
        }

        public View getChildView(int groupPosition, int childPosition, boolean isLastChild,
                View convertView, ViewGroup parent) {
            TextView textView = getGenericView();
            textView.setText(getChild(groupPosition, childPosition).toString());
            return textView;
        }


        public Object getGroup(int groupPosition) {
            return groups[groupPosition];
        }

        public int getGroupCount() {
            return groups.length;
        }

        public long getGroupId(int groupPosition) {
            return groupPosition;
        }

        public View getGroupView(int groupPosition, boolean isExpanded, View convertView,
                ViewGroup parent) {
            TextView textView = (TextView) LayoutInflater.from(getApplicationContext()).inflate(R.layout.header, parent, false);
            textView.setText(getGroup(groupPosition).toString());
            return textView;
        }

        public boolean isChildSelectable(int groupPosition, int childPosition) {
            return true;
        }

        public boolean hasStableIds() {
            return true;
        }


        /**
         * размытие/пропадание хэдера
         */
        public void configurePinnedHeader(View v, int position, int alpha) {
            TextView header = (TextView) v;
            final String title = (String) getGroup(position);

            header.setText(title);
            if (alpha == 255) {
                header.setBackgroundColor(mPinnedHeaderBackgroundColor);
                header.setTextColor(mPinnedHeaderTextColor);
            } else {
                header.setBackgroundColor(Color.argb(alpha, 
                        Color.red(mPinnedHeaderBackgroundColor),
                        Color.green(mPinnedHeaderBackgroundColor),
                        Color.blue(mPinnedHeaderBackgroundColor)));
                header.setTextColor(Color.argb(alpha, 
                        Color.red(mPinnedHeaderTextColor),
                        Color.green(mPinnedHeaderTextColor),
                        Color.blue(mPinnedHeaderTextColor)));
            }
        }

        public void onScroll(AbsListView view, int firstVisibleItem, int visibleItemCount, int totalItemCount) {
            if (view instanceof PinnedHeaderExpListView) {
                ((PinnedHeaderExpListView) view).configureHeaderView(firstVisibleItem);
            }

        }

        public void onScrollStateChanged(AbsListView view, int scrollState) {
            // TODO Auto-generated method stub

        }

    }

}

main.xml

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:id="@+id/root"
    android:orientation="vertical"
    android:layout_width="match_parent"
    android:layout_height="match_parent" >

    <view class="com.example.PinnedHeaderExpListView"
        android:id="@+id/list"
        android:layout_width="match_parent"
        android:layout_height="match_parent" /> 

</LinearLayout>

header.xml

<?xml version="1.0" encoding="utf-8"?>
<TextView xmlns:android="http://schemas.android.com/apk/res/android"
    android:id="@+id/header"
    android:layout_width="match_parent"
    android:layout_height="25dp"
    android:background="@android:color/black" >

</TextView>

It works as expected, except clicking on header. I wish that clicking on header will be equal clicking on group item, but event doesn't even happen and OnClickListener doesnt get control. Why ?

EDIT : clicking on header also works if you add following piece of code inside onCreate() method of ExpandableList.java activity.

        elv.setOnGroupClickListener(new OnGroupClickListener() {

        @Override
        public boolean onGroupClick(ExpandableListView parent, View v,
                int groupPosition, long id) {
            return false;
        }
    });

Answer 2

I've tried to implement Homo Incognito's solution and encounter the same problem of pinned header not being clickable.

The culprit seems to be the ListView itself consuming all the click event thus not passing any to our 'augmented' header view. So you could try digging in ExpandableListView's click handling implementation, which is quite a mess considering its inheritance all the way up to AdapterView.

Instead of trying to highjack the click from ListView, I try circumnavigating such issue by simulating the header click from the list item underneath it. To do so, you need to implement the onChildClick to first see whether the position of the clicked item is underneath the pinned header, if so, then you can relay the click to the true header, if not, then just process the click for that item normally.

In the example below, when the clicked item is underneath the pinned header, I simply made the ListView scrolling to the true header, thus replacing the 'augmented' pinned header with the true header, and the user can take further action from there, e.g. collapsing the group.

Note that such usability flow works only if you don't have any clickable view on the header items, otherwise you will have to do all the click relay and mapping between the pinned virtual header and the true header yourself with onInterceptTouchEvent.

Following Homo Incognito's Code, in PinnedHeaderExpListView.java add the following method:

public int getHeaderViewHeight(){
        return mHeaderViewHeight;
    }

in the activity onCreate, append the following:

elv.setOnChildClickListener(new ExpandableListView.OnChildClickListener() {

        @Override
        public boolean onChildClick(ExpandableListView parent, View v,
                int groupPosition, int childPosition, long id) {

            // we need to obtain the relative y coordinate of the child view, 
            // not its clicked subview, thus first we try to calculate its true index
            long packedPos = ExpandableListView.getPackedPositionForChild(groupPosition, childPosition);
            int viewPos = elv.getFlatListPosition(packedPos) - elv.getFirstVisiblePosition(); 
            View childView = parent.getChildAt(viewPos); // got it


            if (childView.getTop() < elv.getHeaderViewHeight()*.75){
                 // if the clicked child item overlaps more than 25%
                 //  of pinned header, consider it being underneath
                 long groupPackedPos = ExpandableListView.getPackedPositionForGroup(groupPosition);
                 int groupFlatPos = elv.getFlatListPosition(groupPackedPos);
                 elv.smoothScrollToPosition(groupFlatPos);
            }
            return true;
        }
    });