Add a Header to a GridView (Android)


Ask by : robsf February 09, 2015 21:03

I'm aware that the GridView does NOT support a header or footer. I'm extensively using GridViews and I would like to have headers that scroll with it.

What is the best way to approach the problem? Extending the GridView? Extending the ScrollView or ListView?

Any pointer or suggestion would be really appreciated! Thanks!

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Answer by : toobsco42August 06, 2014 16:41

Google's implementation of HeaderGridView addresses this problem. They are subclassing GridView.

HeaderGridView

I believe this is either part of the Google+ Photos app or the Gallery native app.

/*
 * Copyright (C) 2013 The Android Open Source Project
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package com.android.photos.views;
import android.content.Context;
import android.database.DataSetObservable;
import android.database.DataSetObserver;
import android.util.AttributeSet;
import android.view.View;
import android.view.ViewGroup;
import android.widget.AdapterView;
import android.widget.Filter;
import android.widget.Filterable;
import android.widget.FrameLayout;
import android.widget.GridView;
import android.widget.ListAdapter;
import android.widget.WrapperListAdapter;
import java.util.ArrayList;
/**
 * A {@link GridView} that supports adding header rows in a
 * very similar way to {@link ListView}.
 * See {@link HeaderGridView#addHeaderView(View, Object, boolean)}
 */
public class HeaderGridView extends GridView {
    private static final String TAG = "HeaderGridView";
    /**
     * A class that represents a fixed view in a list, for example a header at the top
     * or a footer at the bottom.
     */
    private static class FixedViewInfo {
        /** The view to add to the grid */
        public View view;
        public ViewGroup viewContainer;
        /** The data backing the view. This is returned from {@link ListAdapter#getItem(int)}. */
        public Object data;
        /** <code>true</code> if the fixed view should be selectable in the grid */
        public boolean isSelectable;
    }
    private ArrayList<FixedViewInfo> mHeaderViewInfos = new ArrayList<FixedViewInfo>();
    private void initHeaderGridView() {
        super.setClipChildren(false);
    }
    public HeaderGridView(Context context) {
        super(context);
        initHeaderGridView();
    }
    public HeaderGridView(Context context, AttributeSet attrs) {
        super(context, attrs);
        initHeaderGridView();
    }
    public HeaderGridView(Context context, AttributeSet attrs, int defStyle) {
        super(context, attrs, defStyle);
        initHeaderGridView();
    }
    @Override
    protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
        super.onMeasure(widthMeasureSpec, heightMeasureSpec);
        ListAdapter adapter = getAdapter();
        if (adapter != null && adapter instanceof HeaderViewGridAdapter) {
            ((HeaderViewGridAdapter) adapter).setNumColumns(getNumColumns());
        }
    }
    @Override
    public void setClipChildren(boolean clipChildren) {
       // Ignore, since the header rows depend on not being clipped
    }
    /**
     * Add a fixed view to appear at the top of the grid. If addHeaderView is
     * called more than once, the views will appear in the order they were
     * added. Views added using this call can take focus if they want.
     * <p>
     * NOTE: Call this before calling setAdapter. This is so HeaderGridView can wrap
     * the supplied cursor with one that will also account for header views.
     *
     * @param v The view to add.
     * @param data Data to associate with this view
     * @param isSelectable whether the item is selectable
     */
    public void addHeaderView(View v, Object data, boolean isSelectable) {
        ListAdapter adapter = getAdapter();
        if (adapter != null && ! (adapter instanceof HeaderViewGridAdapter)) {
            throw new IllegalStateException(
                    "Cannot add header view to grid -- setAdapter has already been called.");
        }
        FixedViewInfo info = new FixedViewInfo();
        FrameLayout fl = new FullWidthFixedViewLayout(getContext());
        fl.addView(v);
        info.view = v;
        info.viewContainer = fl;
        info.data = data;
        info.isSelectable = isSelectable;
        mHeaderViewInfos.add(info);
        // in the case of re-adding a header view, or adding one later on,
        // we need to notify the observer
        if (adapter != null) {
            ((HeaderViewGridAdapter) adapter).notifyDataSetChanged();
        }
    }
    /**
     * Add a fixed view to appear at the top of the grid. If addHeaderView is
     * called more than once, the views will appear in the order they were
     * added. Views added using this call can take focus if they want.
     * <p>
     * NOTE: Call this before calling setAdapter. This is so HeaderGridView can wrap
     * the supplied cursor with one that will also account for header views.
     *
     * @param v The view to add.
     */
    public void addHeaderView(View v) {
        addHeaderView(v, null, true);
    }
    public int getHeaderViewCount() {
        return mHeaderViewInfos.size();
    }
    /**
     * Removes a previously-added header view.
     *
     * @param v The view to remove
     * @return true if the view was removed, false if the view was not a header
     *         view
     */
    public boolean removeHeaderView(View v) {
        if (mHeaderViewInfos.size() > 0) {
            boolean result = false;
            ListAdapter adapter = getAdapter();
            if (adapter != null && ((HeaderViewGridAdapter) adapter).removeHeader(v)) {
                result = true;
            }
            removeFixedViewInfo(v, mHeaderViewInfos);
            return result;
        }
        return false;
    }
    private void removeFixedViewInfo(View v, ArrayList<FixedViewInfo> where) {
        int len = where.size();
        for (int i = 0; i < len; ++i) {
            FixedViewInfo info = where.get(i);
            if (info.view == v) {
                where.remove(i);
                break;
            }
        }
    }
    @Override
    public void setAdapter(ListAdapter adapter) {
        if (mHeaderViewInfos.size() > 0) {
            HeaderViewGridAdapter hadapter = new HeaderViewGridAdapter(mHeaderViewInfos, adapter);
            int numColumns = getNumColumns();
            if (numColumns > 1) {
                hadapter.setNumColumns(numColumns);
            }
            super.setAdapter(hadapter);
        } else {
            super.setAdapter(adapter);
        }
    }
    private class FullWidthFixedViewLayout extends FrameLayout {
        public FullWidthFixedViewLayout(Context context) {
            super(context);
        }
        @Override
        protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
            int targetWidth = HeaderGridView.this.getMeasuredWidth()
                    - HeaderGridView.this.getPaddingLeft()
                    - HeaderGridView.this.getPaddingRight();
            widthMeasureSpec = MeasureSpec.makeMeasureSpec(targetWidth,
                    MeasureSpec.getMode(widthMeasureSpec));
            super.onMeasure(widthMeasureSpec, heightMeasureSpec);
        }
    }
    /**
     * ListAdapter used when a HeaderGridView has header views. This ListAdapter
     * wraps another one and also keeps track of the header views and their
     * associated data objects.
     *<p>This is intended as a base class; you will probably not need to
     * use this class directly in your own code.
     */
    private static class HeaderViewGridAdapter implements WrapperListAdapter, Filterable {
        // This is used to notify the container of updates relating to number of columns
        // or headers changing, which changes the number of placeholders needed
        private final DataSetObservable mDataSetObservable = new DataSetObservable();
        private final ListAdapter mAdapter;
        private int mNumColumns = 1;
        // This ArrayList is assumed to NOT be null.
        ArrayList<FixedViewInfo> mHeaderViewInfos;
        boolean mAreAllFixedViewsSelectable;
        private final boolean mIsFilterable;
        public HeaderViewGridAdapter(ArrayList<FixedViewInfo> headerViewInfos, ListAdapter adapter) {
            mAdapter = adapter;
            mIsFilterable = adapter instanceof Filterable;
            if (headerViewInfos == null) {
                throw new IllegalArgumentException("headerViewInfos cannot be null");
            }
            mHeaderViewInfos = headerViewInfos;
            mAreAllFixedViewsSelectable = areAllListInfosSelectable(mHeaderViewInfos);
        }
        public int getHeadersCount() {
            return mHeaderViewInfos.size();
        }
        @Override
        public boolean isEmpty() {
            return (mAdapter == null || mAdapter.isEmpty()) && getHeadersCount() == 0;
        }
        public void setNumColumns(int numColumns) {
            if (numColumns < 1) {
                throw new IllegalArgumentException("Number of columns must be 1 or more");
            }
            if (mNumColumns != numColumns) {
                mNumColumns = numColumns;
                notifyDataSetChanged();
            }
        }
        private boolean areAllListInfosSelectable(ArrayList<FixedViewInfo> infos) {
            if (infos != null) {
                for (FixedViewInfo info : infos) {
                    if (!info.isSelectable) {
                        return false;
                    }
                }
            }
            return true;
        }
        public boolean removeHeader(View v) {
            for (int i = 0; i < mHeaderViewInfos.size(); i++) {
                FixedViewInfo info = mHeaderViewInfos.get(i);
                if (info.view == v) {
                    mHeaderViewInfos.remove(i);
                    mAreAllFixedViewsSelectable = areAllListInfosSelectable(mHeaderViewInfos);
                    mDataSetObservable.notifyChanged();
                    return true;
                }
            }
            return false;
        }
        @Override
        public int getCount() {
            if (mAdapter != null) {
                return getHeadersCount() * mNumColumns + mAdapter.getCount();
            } else {
                return getHeadersCount() * mNumColumns;
            }
        }
        @Override
        public boolean areAllItemsEnabled() {
            if (mAdapter != null) {
                return mAreAllFixedViewsSelectable && mAdapter.areAllItemsEnabled();
            } else {
                return true;
            }
        }
        @Override
        public boolean isEnabled(int position) {
            // Header (negative positions will throw an ArrayIndexOutOfBoundsException)
            int numHeadersAndPlaceholders = getHeadersCount() * mNumColumns;
            if (position < numHeadersAndPlaceholders) {
                return (position % mNumColumns == 0)
                        && mHeaderViewInfos.get(position / mNumColumns).isSelectable;
            }
            // Adapter
            final int adjPosition = position - numHeadersAndPlaceholders;
            int adapterCount = 0;
            if (mAdapter != null) {
                adapterCount = mAdapter.getCount();
                if (adjPosition < adapterCount) {
                    return mAdapter.isEnabled(adjPosition);
                }
            }
            throw new ArrayIndexOutOfBoundsException(position);
        }
        @Override
        public Object getItem(int position) {
            // Header (negative positions will throw an ArrayIndexOutOfBoundsException)
            int numHeadersAndPlaceholders = getHeadersCount() * mNumColumns;
            if (position < numHeadersAndPlaceholders) {
                if (position % mNumColumns == 0) {
                    return mHeaderViewInfos.get(position / mNumColumns).data;
                }
                return null;
            }
            // Adapter
            final int adjPosition = position - numHeadersAndPlaceholders;
            int adapterCount = 0;
            if (mAdapter != null) {
                adapterCount = mAdapter.getCount();
                if (adjPosition < adapterCount) {
                    return mAdapter.getItem(adjPosition);
                }
            }
            throw new ArrayIndexOutOfBoundsException(position);
        }
        @Override
        public long getItemId(int position) {
            int numHeadersAndPlaceholders = getHeadersCount() * mNumColumns;
            if (mAdapter != null && position >= numHeadersAndPlaceholders) {
                int adjPosition = position - numHeadersAndPlaceholders;
                int adapterCount = mAdapter.getCount();
                if (adjPosition < adapterCount) {
                    return mAdapter.getItemId(adjPosition);
                }
            }
            return -1;
        }
        @Override
        public boolean hasStableIds() {
            if (mAdapter != null) {
                return mAdapter.hasStableIds();
            }
            return false;
        }
        @Override
        public View getView(int position, View convertView, ViewGroup parent) {
            // Header (negative positions will throw an ArrayIndexOutOfBoundsException)
            int numHeadersAndPlaceholders = getHeadersCount() * mNumColumns ;
            if (position < numHeadersAndPlaceholders) {
                View headerViewContainer = mHeaderViewInfos
                        .get(position / mNumColumns).viewContainer;
                if (position % mNumColumns == 0) {
                    return headerViewContainer;
                } else {
                    if (convertView == null) {
                        convertView = new View(parent.getContext());
                    }
                    // We need to do this because GridView uses the height of the last item
                    // in a row to determine the height for the entire row.
                    convertView.setVisibility(View.INVISIBLE);
                    convertView.setMinimumHeight(headerViewContainer.getHeight());
                    return convertView;
                }
            }
            // Adapter
            final int adjPosition = position - numHeadersAndPlaceholders;
            int adapterCount = 0;
            if (mAdapter != null) {
                adapterCount = mAdapter.getCount();
                if (adjPosition < adapterCount) {
                    return mAdapter.getView(adjPosition, convertView, parent);
                }
            }
            throw new ArrayIndexOutOfBoundsException(position);
        }
        @Override
        public int getItemViewType(int position) {
            int numHeadersAndPlaceholders = getHeadersCount() * mNumColumns;
            if (position < numHeadersAndPlaceholders && (position % mNumColumns != 0)) {
                // Placeholders get the last view type number
                return mAdapter != null ? mAdapter.getViewTypeCount() : 1;
            }
            if (mAdapter != null && position >= numHeadersAndPlaceholders) {
                int adjPosition = position - numHeadersAndPlaceholders;
                int adapterCount = mAdapter.getCount();
                if (adjPosition < adapterCount) {
                    return mAdapter.getItemViewType(adjPosition);
                }
            }
            return AdapterView.ITEM_VIEW_TYPE_HEADER_OR_FOOTER;
        }
        @Override
        public int getViewTypeCount() {
            if (mAdapter != null) {
                return mAdapter.getViewTypeCount() + 1;
            }
            return 2;
        }
        @Override
        public void registerDataSetObserver(DataSetObserver observer) {
            mDataSetObservable.registerObserver(observer);
            if (mAdapter != null) {
                mAdapter.registerDataSetObserver(observer);
            }
        }
        @Override
        public void unregisterDataSetObserver(DataSetObserver observer) {
            mDataSetObservable.unregisterObserver(observer);
            if (mAdapter != null) {
                mAdapter.unregisterDataSetObserver(observer);
            }
        }
        @Override
        public Filter getFilter() {
            if (mIsFilterable) {
                return ((Filterable) mAdapter).getFilter();
            }
            return null;
        }
        @Override
        public ListAdapter getWrappedAdapter() {
            return mAdapter;
        }
        public void notifyDataSetChanged() {
            mDataSetObservable.notifyChanged();
        }
    }
}
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