Java tutorial
/* * Copyright 2014 Eduardo Barrenechea * * 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.youth.xframe.adapter.decoration; import android.graphics.Canvas; import android.graphics.Rect; import android.support.v4.view.ViewCompat; import android.support.v7.widget.RecyclerView; import android.view.View; import android.view.ViewGroup; import com.youth.xframe.adapter.XRecyclerViewAdapter; import java.util.HashMap; import java.util.Map; /** * A sticky header decoration for android's RecyclerView. */ public class StickyHeaderDecoration extends RecyclerView.ItemDecoration { /** * The adapter to assist the {@link StickyHeaderDecoration} in creating and binding the header views. * * @param <T> the header view holder */ public interface IStickyHeaderAdapter<T extends RecyclerView.ViewHolder> { /** * Returns the header id for the item at the given position. * The item in one group should return the same HeaderId. * * @param position the item position * @return the header id */ long getHeaderId(int position); /** * Creates a new header ViewHolder. * * @param parent the header's view parent * @return a view holder for the created view */ T onCreateHeaderViewHolder(ViewGroup parent); /** * Updates the header view to reflect the header data for the given position * @param viewholder the header view holder * @param position the header's item position */ void onBindHeaderViewHolder(T viewholder, int position); } public static final long NO_HEADER_ID = -1L; private Map<Long, RecyclerView.ViewHolder> mHeaderCache; private IStickyHeaderAdapter mAdapter; private boolean mRenderInline; private boolean mIncludeHeader = false; /** * @param adapter * the sticky header adapter to use */ public StickyHeaderDecoration(IStickyHeaderAdapter adapter) { this(adapter, false); } /** * @param adapter * the sticky header adapter to use */ public StickyHeaderDecoration(IStickyHeaderAdapter adapter, boolean renderInline) { mAdapter = adapter; mHeaderCache = new HashMap<>(); mRenderInline = renderInline; } public void setIncludeHeader(boolean mIncludeHeader) { this.mIncludeHeader = mIncludeHeader; } /** * {@inheritDoc} */ @Override public void getItemOffsets(Rect outRect, View view, RecyclerView parent, RecyclerView.State state) { int position = parent.getChildAdapterPosition(view); int headerHeight = 0; if (!mIncludeHeader) { if (parent.getAdapter() instanceof XRecyclerViewAdapter) { int headerCount = ((XRecyclerViewAdapter) parent.getAdapter()).getHeaderCount(); int footerCount = ((XRecyclerViewAdapter) parent.getAdapter()).getFooterCount(); int dataCount = ((XRecyclerViewAdapter) parent.getAdapter()).getDataCount(); if (position < headerCount) { return; } if (position >= headerCount + dataCount) { return; } if (position >= headerCount) { position -= headerCount; } } } if (position != RecyclerView.NO_POSITION && hasHeader(position) && showHeaderAboveItem(position)) { View header = getHeader(parent, position).itemView; headerHeight = getHeaderHeightForLayout(header); } outRect.set(0, headerHeight, 0, 0); } private boolean showHeaderAboveItem(int itemAdapterPosition) { if (itemAdapterPosition == 0) { return true; } return mAdapter.getHeaderId(itemAdapterPosition - 1) != mAdapter.getHeaderId(itemAdapterPosition); } /** * Clears the header view cache. Headers will be recreated and * rebound on list scroll after this method has been called. */ public void clearHeaderCache() { mHeaderCache.clear(); } public View findHeaderViewUnder(float x, float y) { for (RecyclerView.ViewHolder holder : mHeaderCache.values()) { final View child = holder.itemView; final float translationX = ViewCompat.getTranslationX(child); final float translationY = ViewCompat.getTranslationY(child); if (x >= child.getLeft() + translationX && x <= child.getRight() + translationX && y >= child.getTop() + translationY && y <= child.getBottom() + translationY) { return child; } } return null; } private boolean hasHeader(int position) { return mAdapter.getHeaderId(position) != NO_HEADER_ID; } private RecyclerView.ViewHolder getHeader(RecyclerView parent, int position) { final long key = mAdapter.getHeaderId(position); if (mHeaderCache.containsKey(key)) { return mHeaderCache.get(key); } else { final RecyclerView.ViewHolder holder = mAdapter.onCreateHeaderViewHolder(parent); final View header = holder.itemView; //noinspection unchecked mAdapter.onBindHeaderViewHolder(holder, position); int widthSpec = View.MeasureSpec.makeMeasureSpec(parent.getMeasuredWidth(), View.MeasureSpec.EXACTLY); int heightSpec = View.MeasureSpec.makeMeasureSpec(parent.getMeasuredHeight(), View.MeasureSpec.UNSPECIFIED); int childWidth = ViewGroup.getChildMeasureSpec(widthSpec, parent.getPaddingLeft() + parent.getPaddingRight(), header.getLayoutParams().width); int childHeight = ViewGroup.getChildMeasureSpec(heightSpec, parent.getPaddingTop() + parent.getPaddingBottom(), header.getLayoutParams().height); header.measure(childWidth, childHeight); header.layout(0, 0, header.getMeasuredWidth(), header.getMeasuredHeight()); mHeaderCache.put(key, holder); return holder; } } /** * {@inheritDoc} */ @Override public void onDrawOver(Canvas canvas, RecyclerView parent, RecyclerView.State state) { if (parent.getAdapter() == null) { return; } final int count = parent.getChildCount(); long previousHeaderId = -1; for (int layoutPos = 0; layoutPos < count; layoutPos++) { final View child = parent.getChildAt(layoutPos); int adapterPos = parent.getChildAdapterPosition(child); if (!mIncludeHeader) { if (parent.getAdapter() instanceof XRecyclerViewAdapter) { int headerCount = ((XRecyclerViewAdapter) parent.getAdapter()).getHeaderCount(); int footerCount = ((XRecyclerViewAdapter) parent.getAdapter()).getFooterCount(); int dataCount = ((XRecyclerViewAdapter) parent.getAdapter()).getDataCount(); if (adapterPos < headerCount) { continue; } if (adapterPos >= headerCount + dataCount) { continue; } if (adapterPos >= headerCount) { adapterPos -= headerCount; } } } if (adapterPos != RecyclerView.NO_POSITION && hasHeader(adapterPos)) { long headerId = mAdapter.getHeaderId(adapterPos); if (headerId != previousHeaderId) { previousHeaderId = headerId; View header = getHeader(parent, adapterPos).itemView; canvas.save(); final int left = child.getLeft(); final int top = getHeaderTop(parent, child, header, adapterPos, layoutPos); canvas.translate(left, top); header.setTranslationX(left); header.setTranslationY(top); header.draw(canvas); canvas.restore(); } } } } private int getHeaderTop(RecyclerView parent, View child, View header, int adapterPos, int layoutPos) { int headerHeight = getHeaderHeightForLayout(header); int top = ((int) child.getY()) - headerHeight; if (layoutPos == 0) { final int count = parent.getChildCount(); final long currentId = mAdapter.getHeaderId(adapterPos); // find next view with header and compute the offscreen push if needed for (int i = 1; i < count; i++) { int adapterPosHere = parent.getChildAdapterPosition(parent.getChildAt(i)); if (adapterPosHere != RecyclerView.NO_POSITION) { long nextId = mAdapter.getHeaderId(adapterPosHere); if (nextId != currentId) { final View next = parent.getChildAt(i); final int offset = ((int) next.getY()) - (headerHeight + getHeader(parent, adapterPosHere).itemView.getHeight()); if (offset < 0) { return offset; } else { break; } } } } top = Math.max(0, top); } return top; } private int getHeaderHeightForLayout(View header) { return mRenderInline ? 0 : header.getHeight(); } }