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这篇文章主要介绍Android RecyclerView如何实现多种item布局,文中介绍的非常详细,具有一定的参考价值,感兴趣的小伙伴们一定要看完!
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在项目中列表是基本都会用到的,然而在显示列表时,我们需要的数据可能需要不止一种item显示,对于复杂的数据就需要多种item,以不同的样式显示出来,这样效果是很棒的,我们先看一下效果
我们可以看到,这个RecyclerView中有多种item显示出来,那么具体怎么实现呢,其实在RecyclerView中,我们可以重写方法getItemViewType(),这个方法会传进一个参数position表示当前是第几个Item,然后我们可以通过position拿到当前的Item对象,然后判断这个item对象需要那种视图,返回一个int类型的视图标志,然后在onCreatViewHolder方法中给引入布局,这样就能够实现多种item显示了,讲了这么多我们看一下具体的例子
@Override public int getItemViewType(int position) { if(list.size() == 0){ return EMPTY_VIEW; } else if(list.get(position) == null){ return PROGRESS_VIEW; } else if(list.get(position).getType().equals(News.IMAGE_NEWS)){ return IMAGE_VIEW; } else { return super.getItemViewType(position); } }
首先我们重写了getItemViewType这个方法,在这个方法中根据position对item对象做了一些判断,如果存储item对象的集合大小为空,返回空view标识(这里为1),如果item对象为null,返回进度条标识,这个主要是用于实现下拉加载更多,如果item对象类型属于图片类型,就返回图片类型对应的Item,这个就是效果图中的第一个Item类型,否则就是其它类型,也就是效果图中的另一种item布局,然后我们在onCreatViewHolder中具体的为每一种类型引入其布局
@Override public RecyclerView.ViewHolder onCreateViewHolder(ViewGroup parent, int viewType) { View view; if(viewType == PROGRESS_VIEW){ view = LayoutInflater.from(parent.getContext()).inflate(R.layout.progressbar_item, parent, false); return new ProgressViewHolder(view); } else if(viewType == EMPTY_VIEW){ return null; } else if(viewType == IMAGE_VIEW){ view = LayoutInflater.from(parent.getContext()).inflate(R.layout.image_news_item, parent, false); return new ImageViewHolder(view); } else { view = LayoutInflater.from(parent.getContext()).inflate(R.layout.news_item, parent, false); return new NewsViewHolder(view); } }
上面的代码就是具体为每种viewType引入其对应的布局,这样就基本实现了多种item布局,但是仅仅是这些还不够,因为我们还要对每种item设置数据,所以还要对每种item写一个VIewHolder来为item显示数据
class NewsViewHolder extends RecyclerView.ViewHolder{ @BindView(R.id.news_title)TextView title; @BindView(R.id.news_digest)TextView digest; @BindView(R.id.news_time)TextView time; @BindView(R.id.news_src)ImageView image; public NewsViewHolder(View itemView) { super(itemView); ButterKnife.bind(this, itemView); } } class ImageViewHolder extends RecyclerView.ViewHolder{ @BindView(R.id.news_title) TextView title; @BindView(R.id.image_left) ImageView imageLeft; @BindView(R.id.image_right) ImageView imageRight; @BindView(R.id.image_middle) ImageView imageMiddle; @BindView(R.id.news_time) TextView time; public ImageViewHolder(View itemView) { super(itemView); ButterKnife.bind(this, itemView); } } class ProgressViewHolder extends RecyclerView.ViewHolder { @BindView(R.id.progressBar) ProgressBar progressBar; @BindView(R.id.textView) TextView textView; public ProgressViewHolder(View itemView) { super(itemView); ButterKnife.bind(this, itemView); } }
上面就是item对应的几个ViewHolder,判断viewHolder属于那种对象,然后在onBindViewHolder中根据对应的ViewHolder对其控件设置数据并显示
@Override public void onBindViewHolder(RecyclerView.ViewHolder holder, final int position) { holder.itemView.setOnClickListener(new View.OnClickListener() { @Override public void onClick(View v) { clickListener.onItemClick(v, position); } }); if(holder instanceof NewsViewHolder){ NewsViewHolder viewHolder = (NewsViewHolder)holder; viewHolder.title.setText(list.get(position).getTitle()); viewHolder.time.setText(list.get(position).getTime()); /** * Glide加载图片 */ Glide.with(context).load(list.get(position).getImageUrl().get(0)) .override(dpToPx(72), dpToPx(72)).centerCrop().into(viewHolder.image); if(list.get(position).getType().equals(News.TEXT_NEWS)){ viewHolder.digest.setText(list.get(position).getDigest()); } else { viewHolder.digest.setText(""); } } else if(holder instanceof ImageViewHolder){ ImageViewHolder viewHolder = (ImageViewHolder)holder; viewHolder.title.setText(list.get(position).getTitle()); viewHolder.time.setText(list.get(position).getTime()); setItemImage(viewHolder, list, position); } else if(holder instanceof ProgressViewHolder){ ProgressViewHolder viewHolder = (ProgressViewHolder)holder; viewHolder.progressBar.setIndeterminate(true); } }
整个过程基本就是这样,这种方式在项目中经常会用到,我们就可以这样去处理,下拉加载更多就可以这样实现,在加载完数据后再往对象集合中传入null,然后判断如果出现null就加载progressBar布局,再加上Google官方的SwipeRefreshLayout,下拉刷新,上拉加载就搞定了,其实很容易,而且也有点Material Design 的感觉~~~~~~
看下Adapter的全部代码
package com.zmt.e_read.Adapter; import android.content.Context; import android.support.v7.widget.RecyclerView; import android.util.DisplayMetrics; import android.view.LayoutInflater; import android.view.View; import android.view.ViewGroup; import android.widget.ImageView; import android.widget.TextView; import com.bumptech.glide.Glide; import com.zmt.e_read.Module.News; import com.zmt.e_read.Module.OnItemClickListener; import com.zmt.e_read.R; import com.zmt.e_read.Utils.ProgressViewHolder; import java.util.Collection; import java.util.Collections; import java.util.List; import butterknife.BindView; import butterknife.ButterKnife; /** * Created by Dangelo on 2016/9/27. */ public class NewsAdapter extends RecyclerView.Adapter{ private final int EMPTY_VIEW = 1; private final int PROGRESS_VIEW = 2; private final int IMAGE_VIEW = 3; private Context context; private List list; private OnItemClickListener clickListener; public NewsAdapter(Context context, List list, OnItemClickListener clickListener) { this.context = context; this.list = list; this.clickListener = clickListener; } public void addOnItemClickListener(OnItemClickListener clickListener){ this.clickListener = clickListener; } @Override public int getItemViewType(int position) { if(list.size() == 0){ return EMPTY_VIEW; } else if(list.get(position) == null){ return PROGRESS_VIEW; } else if(list.get(position).getType().equals(News.IMAGE_NEWS)){ return IMAGE_VIEW; } else { return super.getItemViewType(position); } } @Override public RecyclerView.ViewHolder onCreateViewHolder(ViewGroup parent, int viewType) { View view; if(viewType == PROGRESS_VIEW){ view = LayoutInflater.from(parent.getContext()).inflate(R.layout.progressbar_item, parent, false); return new ProgressViewHolder(view); } else if(viewType == EMPTY_VIEW){ return null; } else if(viewType == IMAGE_VIEW){ view = LayoutInflater.from(parent.getContext()).inflate(R.layout.image_news_item, parent, false); return new ImageViewHolder(view); } else { view = LayoutInflater.from(parent.getContext()).inflate(R.layout.news_item, parent, false); return new NewsViewHolder(view); } } @Override public void onBindViewHolder(RecyclerView.ViewHolder holder, final int position) { holder.itemView.setOnClickListener(new View.OnClickListener() { @Override public void onClick(View v) { clickListener.onItemClick(v, position); } }); if(holder instanceof NewsViewHolder){ NewsViewHolder viewHolder = (NewsViewHolder)holder; viewHolder.title.setText(list.get(position).getTitle()); viewHolder.time.setText(list.get(position).getTime()); /** * Glide加载图片 */ Glide.with(context).load(list.get(position).getImageUrl().get(0)) .override(dpToPx(72), dpToPx(72)).centerCrop().into(viewHolder.image); if(list.get(position).getType().equals(News.TEXT_NEWS)){ viewHolder.digest.setText(list.get(position).getDigest()); } else { viewHolder.digest.setText(""); } } else if(holder instanceof ImageViewHolder){ ImageViewHolder viewHolder = (ImageViewHolder)holder; viewHolder.title.setText(list.get(position).getTitle()); viewHolder.time.setText(list.get(position).getTime()); setItemImage(viewHolder, list, position); } else if(holder instanceof ProgressViewHolder){ ProgressViewHolder viewHolder = (ProgressViewHolder)holder; viewHolder.progressBar.setIndeterminate(true); } } public void setItemImage(ImageViewHolder viewHolder, List list, int position){ viewHolder.imageMiddle.setVisibility(View.VISIBLE); viewHolder.imageRight.setVisibility(View.VISIBLE); DisplayMetrics displayMetrics = context.getResources().getDisplayMetrics(); if(list.get(position).getImageUrl().size() == 1){ Glide.with(context).load(list.get(position).getImageUrl().get(0)) .override(displayMetrics.widthPixels - dpToPx(10), dpToPx(90)) .centerCrop().into(viewHolder.imageLeft); viewHolder.imageMiddle.setVisibility(View.GONE); viewHolder.imageRight.setVisibility(View.GONE); } else if(list.get(position).getImageUrl().size() == 2){ int imageWidth = (displayMetrics.widthPixels - dpToPx(20)) / 2; Glide.with(context).load(list.get(position).getImageUrl().get(0)) .override(imageWidth, dpToPx(90)) .centerCrop().into(viewHolder.imageLeft); Glide.with(context).load(list.get(position).getImageUrl().get(1)) .override(imageWidth, dpToPx(90)) .centerCrop().into(viewHolder.imageMiddle); viewHolder.imageRight.setVisibility(View.GONE); } else if(list.get(position).getImageUrl().size() >= 3){ int imageWidth = (displayMetrics.widthPixels - dpToPx(30)) / 3; Glide.with(context).load(list.get(position).getImageUrl().get(0)) .override(imageWidth, dpToPx(90)) .centerCrop().into(viewHolder.imageLeft); Glide.with(context).load(list.get(position).getImageUrl().get(1)) .override(imageWidth, dpToPx(90)) .centerCrop().into(viewHolder.imageMiddle); Glide.with(context).load(list.get(position).getImageUrl().get(2)) .override(imageWidth, dpToPx(90)) .centerCrop().into(viewHolder.imageRight); } } @Override public int getItemCount() { return list.size(); } public int dpToPx(float dp){ float px = context.getResources().getDisplayMetrics().density; return (int)(dp * px + 0.5f); } class NewsViewHolder extends RecyclerView.ViewHolder{ @BindView(R.id.news_title)TextView title; @BindView(R.id.news_digest)TextView digest; @BindView(R.id.news_time)TextView time; @BindView(R.id.news_src)ImageView image; public NewsViewHolder(View itemView) { super(itemView); ButterKnife.bind(this, itemView); } } class ImageViewHolder extends RecyclerView.ViewHolder{ @BindView(R.id.news_title) TextView title; @BindView(R.id.image_left) ImageView imageLeft; @BindView(R.id.image_right) ImageView imageRight; @BindView(R.id.image_middle) ImageView imageMiddle; @BindView(R.id.news_time) TextView time; public ImageViewHolder(View itemView) { super(itemView); ButterKnife.bind(this, itemView); } } class ProgressViewHolder extends RecyclerView.ViewHolder { @BindView(R.id.progressBar) ProgressBar progressBar; @BindView(R.id.textView) TextView textView; public ProgressViewHolder(View itemView) { super(itemView); ButterKnife.bind(this, itemView); } } }
最后说一下为什么为什么用RecyclerView取代ListView。
用过ListView的都知道,在ListView中若要复用视图缓存,就要在getView()方法中手动判断convertView是否为空,若不为空则复用视图缓存,若为空则重新加载视图,而RecyclerView相当于对ListView的Adapter进行了再次封装,把ListView手动判断是否有缓存的代码封装到RecyclerView内部,使这部分逻辑不可见,我们只需要通过getItemCount()方法告诉RecyclerView有多少项数据,然后在onCreateViewHolder()中加载item布局实例化ViewHolder,然后在onBindViewHolder()中完成数据的绑定即可。
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