最近開啟SDK Manager蚣抗，突然發(fā)現(xiàn)android7.0的都有了瘫怜，這迭代升級(jí)還真快扇售。不過國內(nèi)普遍手機(jī)還是停留在4.4+，多則是是處于5.0版本的膝藕。Android5.0變化非常大式廷，引入material design，加強(qiáng)權(quán)限管理束莫、減少功耗...好像扯遠(yuǎn)了0 0±撩蓿現(xiàn)在直接進(jìn)入主題。在這里先感謝讀者的支持＠缆獭策严！
筆者前陣子寫了一個(gè)萬能適配器，提供了上拉加載饿敲、上拉刷新的基礎(chǔ)功能妻导，重要的是一個(gè)基礎(chǔ)baseAdapter能夠支持ListView與RecyclerView，后期提供傳送門怀各，現(xiàn)在我打算一步驟一步驟講下我的實(shí)現(xiàn)思路倔韭。
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<h3 align = "center">實(shí)戰(zhàn)RecyclerView頭部尾部添加方法 </h4>
效果圖如下：
一、前提
首先ListView與RecyclerView兩者非常相似瓢对，兩者提供view都是依賴適配器寿酌。只不過就是5.0版本推出RecyclerView后，Google將adapter和viewHolder做了一系列的優(yōu)化和封裝硕蛹。不像之前為了復(fù)用Listview里面的converView醇疼，要類似在getView里面實(shí)現(xiàn)下列的代碼：
上面代碼看起來挺眼熟吧~
二、對(duì)比RecyclerView法焰，google進(jìn)行的優(yōu)化
在RecyclerView依賴的適配器中秧荆，無論是適配器還是ViewHolder，從源碼我們可以看出埃仪，都存在RecyclerView的匿名內(nèi)部類乙濒。相對(duì)于Listview，RecyclerView內(nèi)置了多級(jí)緩存卵蛉、RecyclerViewPool（從線程的角度颁股，可以理解成類似線程池的東西么库，即多個(gè)RecyclerView可以公用一個(gè)view）、ViewHolder(已經(jīng)實(shí)現(xiàn)了復(fù)用豌蟋，相對(duì)于Listview的BaseAdapter中g(shù)etView方法需要開發(fā)者自己引入復(fù)用問題方便很多)等等廊散。這里我們簡單說下兩個(gè)方法：
public ViewHolder onCreateViewHolder(ViewGroup parent, int viewType)
public void onBindViewHolder(ViewHolder holder, int position)
在以前的BaseAdapter中,所有視圖加載、數(shù)據(jù)綁定以及復(fù)用梧疲，都需要我們直接在getView里面進(jìn)行操作。onCreateViewHolder負(fù)責(zé)視圖加載并且內(nèi)部完成復(fù)用运准，onBindViewHolder負(fù)責(zé)數(shù)據(jù)綁定并且內(nèi)部完成一系列的緩存機(jī)制幌氮。這里滿足了視圖層與邏輯層的分離，典型的mvp模式胁澳。
三该互、RecyclerView的頭部與尾部實(shí)現(xiàn)
RecyclerView不像ListView擁有addHeaderView()與addFooterView()的方法簡單添加頭部尾部即可，而且RecyclerView也沒有像ListView的列表點(diǎn)擊監(jiān)聽方法（setItemOnclickListener）韭畸，這里我也不明白為什么官方會(huì)取消了這些獨(dú)有的屬性宇智，不過我們依然可以在onBindViewHolder方法中進(jìn)行事件綁定！
具體頭部與尾部實(shí)現(xiàn)方法胰丁，這里有個(gè)訣竅随橘，這里先看一個(gè)方法：
public int getItemViewType(int position)
getItemViewType方法是在執(zhí)行onCreateViewHolder(ViewGroup parent, int viewType)前回調(diào)用viewType，目的是為了根據(jù)viewType不同創(chuàng)建不同的視圖锦庸。我們可以通過在onCreateViewHolder創(chuàng)建視圖的時(shí)候机蔗，對(duì)viewType進(jìn)行判斷，如果添加了頭部甘萧，在position = 0的時(shí)候回調(diào)頭部的viewType給onCreateViewHolder萝嘁，從而創(chuàng)建頭部。尾部創(chuàng)建方法于此類同扬卷，直接看下代碼牙言，適配器的實(shí)現(xiàn)：
package cn.wsy.recyclerdemo;
import android.content.Context;
import android.support.v7.widget.GridLayoutManager;
import android.support.v7.widget.RecyclerView;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.TextView;
import java.util.ArrayList;
import java.util.List;
/**
* Created by wsy on 2016/8/4.
*/
public class MyAdapter extends RecyclerView.Adapter<MyAdapter.MyHolder> {
private RecyclerView mRecyclerView;
private List<String> data = new ArrayList<>();
private Context mContext;
private View VIEW_FOOTER;
private View VIEW_HEADER;
//Type
private int TYPE_NORMAL = 1000;
private int TYPE_HEADER = 1001;
private int TYPE_FOOTER = 1002;
public MyAdapter(List<String> data, Context mContext) {
this.data = data;
this.mContext = mContext;
}
@Override
public MyAdapter.MyHolder onCreateViewHolder(ViewGroup parent, int viewType) {
if (viewType == TYPE_FOOTER) {
return new MyHolder(VIEW_FOOTER);
} else if (viewType == TYPE_HEADER) {
return new MyHolder(VIEW_HEADER);
} else {
return new MyHolder(getLayout(R.layout.item_list_layout));
}
}
@Override
public void onBindViewHolder(MyHolder holder, int position) {
if (!isHeaderView(position) && !isFooterView(position)) {
if (haveHeaderView()) position--;
TextView content = (TextView) holder.itemView.findViewById(R.id.item_content);
TextView time = (TextView) holder.itemView.findViewById(R.id.item_time);
content.setText(data.get(position));
time.setText("2016-1-1");
}
}
@Override
public int getItemCount() {
int count = (data == null ? 0 : data.size());
if (VIEW_FOOTER != null) {
count++;
}
if (VIEW_HEADER != null) {
count++;
}
return count;
}
@Override
public int getItemViewType(int position) {
if (isHeaderView(position)) {
return TYPE_HEADER;
} else if (isFooterView(position)) {
return TYPE_FOOTER;
} else {
return TYPE_NORMAL;
}
}
@Override
public void onAttachedToRecyclerView(RecyclerView recyclerView) {
try {
if (mRecyclerView == null && mRecyclerView != recyclerView) {
mRecyclerView = recyclerView;
}
ifGridLayoutManager();
} catch (Exception e) {
e.printStackTrace();
}
}
private View getLayout(int layoutId) {
return LayoutInflater.from(mContext).inflate(layoutId, null);
}
public void addHeaderView(View headerView) {
if (haveHeaderView()) {
throw new IllegalStateException("hearview has already exists!");
} else {
//避免出現(xiàn)寬度自適應(yīng)
ViewGroup.LayoutParams params = new ViewGroup.LayoutParams(ViewGroup.LayoutParams.MATCH_PARENT, ViewGroup.LayoutParams.WRAP_CONTENT);
headerView.setLayoutParams(params);
VIEW_HEADER = headerView;
ifGridLayoutManager();
notifyItemInserted(0);
}
}
public void addFooterView(View footerView) {
if (haveFooterView()) {
throw new IllegalStateException("footerView has already exists!");
} else {
ViewGroup.LayoutParams params = new ViewGroup.LayoutParams(ViewGroup.LayoutParams.MATCH_PARENT, ViewGroup.LayoutParams.WRAP_CONTENT);
footerView.setLayoutParams(params);
VIEW_FOOTER = footerView;
ifGridLayoutManager();
notifyItemInserted(getItemCount() - 1);
}
}
private void ifGridLayoutManager() {
if (mRecyclerView == null) return;
final RecyclerView.LayoutManager layoutManager = mRecyclerView.getLayoutManager();
if (layoutManager instanceof GridLayoutManager) {
final GridLayoutManager.SpanSizeLookup originalSpanSizeLookup =
((GridLayoutManager) layoutManager).getSpanSizeLookup();
((GridLayoutManager) layoutManager).setSpanSizeLookup(new GridLayoutManager.SpanSizeLookup() {
@Override
public int getSpanSize(int position) {
return (isHeaderView(position) || isFooterView(position)) ?
((GridLayoutManager) layoutManager).getSpanCount() :
1;
}
});
}
}
private boolean haveHeaderView() {
return VIEW_HEADER != null;
}
public boolean haveFooterView() {
return VIEW_FOOTER != null;
}
private boolean isHeaderView(int position) {
return haveHeaderView() && position == 0;
}
private boolean isFooterView(int position) {
return haveFooterView() && position == getItemCount() - 1;
}
public static class MyHolder extends RecyclerView.ViewHolder {
public MyHolder(View itemView) {
super(itemView);
}
}
}
四、實(shí)現(xiàn)方法
簡單的初始化RecycerView怪得，以及設(shè)置適配器咱枉，如下：
private void initRecyc() {
// mRecyclerView.setLayoutManager(new GridLayoutManager(this,2));
mRecyclerView.setLayoutManager(new LinearLayoutManager(this));
adapter = new MyAdapter(data, this);
mRecyclerView.setAdapter(adapter);
adapter.addFooterView(LayoutInflater.from(this).inflate(R.layout.item_footer_layout,null));
adapter.addHeaderView(LayoutInflater.from(this).inflate(R.layout.item_header_layout,null));
}
五、注意的問題
筆者在添加頭部尾部的時(shí)候汇恤，發(fā)現(xiàn)在配置RecyclerView庞钢，如果模式是配置GridLayoutManager的時(shí)候，發(fā)現(xiàn)頭部會(huì)跑到第一格因谎，也就是不是自己想要獨(dú)立一行的效果基括，這里貼上關(guān)鍵代碼，可以解決（簡單數(shù)學(xué)問題啦哈~）：
private void ifGridLayoutManager() {
if (mRecyclerView == null) return;
final RecyclerView.LayoutManager layoutManager = mRecyclerView.getLayoutManager();
if (layoutManager instanceof GridLayoutManager) {
final GridLayoutManager.SpanSizeLookup originalSpanSizeLookup =
((GridLayoutManager) layoutManager).getSpanSizeLookup();
((GridLayoutManager) layoutManager).setSpanSizeLookup(new GridLayoutManager.SpanSizeLookup() {
@Override
public int getSpanSize(int position) {
return (isHeaderView(position) || isFooterView(position)) ?
((GridLayoutManager) layoutManager).getSpanCount() :
1;
}
});
}
}
傻小孩b 共勉
寫給一起奮斗的你
2016年8月4日
