RecyclerView怎么在Android中使用
RecyclerView怎么在Android中使用?相信很多没有经验的人对此束手无策,为此本文总结了问题出现的原因和解决方法,通过这篇文章希望你能解决这个问题。
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首先ListView与RecyclerView两者非常相似,两者提供view都是依赖适配器。只不过就是5.0版本推出RecyclerView后,Google将adapter和viewHolder做了一系列的优化和封装。不像之前为了复用Listview里面的converView,要类似在getView里面实现下列的代码:
上面代码看起来挺眼熟吧~
二、对比RecyclerView,google进行的优化
在RecyclerView依赖的适配器中,无论是适配器还是ViewHolder,从源码我们可以看出,都存在RecyclerView的匿名内部类。相对于Listview,RecyclerView内置了多级缓存、RecyclerViewPool(从线程的角度,可以理解成类似线程池的东西,即多个RecyclerView可以公用一个view)、ViewHolder(已经实现了复用,相对于Listview的BaseAdapter中getView方法需要开发者自己引入复用问题方便很多)等等。这里我们简单说下两个方法:
public ViewHolder onCreateViewHolder(ViewGroup parent, int viewType)
public void onBindViewHolder(ViewHolder holder, int position)
在以前的BaseAdapter中,所有视图加载、数据绑定以及复用,都需要我们直接在getView里面进行操作。onCreateViewHolder负责视图加载并且内部完成复用,onBindViewHolder负责数据绑定并且内部完成一系列的缓存机制。这里满足了视图层与逻辑层的分离,典型的mvp模式。
三、RecyclerView的头部与尾部实现
RecyclerView不像ListView拥有addHeaderView()与addFooterView()的方法简单添加头部尾部即可,而且RecyclerView也没有像ListView的列表点击监听方法(setItemOnclickListener),这里我也不明白为什么官方会取消了这些独有的属性,不过我们依然可以在onBindViewHolder方法中进行事件绑定!
具体头部与尾部实现方法,这里有个诀窍,这里先看一个方法:
public int getItemViewType(int position)
getItemViewType方法是在执行onCreateViewHolder(ViewGroup parent, int viewType)前回调用viewType,目的是为了根据viewType不同创建不同的视图。我们可以通过在onCreateViewHolder创建视图的时候,对viewType进行判断,如果添加了头部,在position = 0的时候回调头部的viewType给onCreateViewHolder,从而创建头部。尾部创建方法于此类同,直接看下代码,适配器的实现:
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{ private RecyclerView mRecyclerView; private List 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 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 { //避免出现宽度自适应 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、实现方法
简单的初始化RecycerView,以及设置适配器,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、注意的问题
笔者在添加头部尾部的时候,发现在配置RecyclerView,如果模式是配置GridLayoutManager的时候,发现头部会跑到第一格,也就是不是自己想要独立一行的效果,这里贴上关键代码,可以解决(简单数学问题啦哈~):
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; } }); } }
看完上述内容,你们掌握RecyclerView怎么在Android中使用的方法了吗?如果还想学到更多技能或想了解更多相关内容,欢迎关注创新互联行业资讯频道,感谢各位的阅读!
名称栏目:RecyclerView怎么在Android中使用
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