进击的RecyclerView入门一（简单上手）

虽然RecyclerView面世有一段时间了，但由于它的学习成本相对较高，很多码友只是粗略的认识了一下而没有细致的品味RecyclerView的真谛。

那么从现在开始我将带你装逼带你飞，一起领略Google工程师们赋予RecyclerView独特的魅力。

首先我们看一下官方文档是怎么介绍RecyclerView的简介：

A flexible view for providing a limited window into a large data set.

Google的工程师写文档还真够精辟的，写的什么鬼？这不等于没写吗？OK，别激动，我们慢慢来。先看看怎么样把RecyclerView跑起来？

接下来简单写一个使用RecyclerView加载网络图片的demo。

布局文件如下：

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context="com.zqlite.android.recyclerviewadvance.MainActivity">

    <android.support.v7.widget.RecyclerView
        android:id="@+id/recyclerView"
        android:layout_width="match_parent"
        android:layout_height="match_parent">
    </android.support.v7.widget.RecyclerView>
</RelativeLayout>

Activity文件如下：

package com.zqlite.android.recyclerviewadvance;

import android.media.Image;
import android.os.Handler;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.support.v7.widget.CardView;
import android.support.v7.widget.DefaultItemAnimator;
import android.support.v7.widget.GridLayoutManager;
import android.support.v7.widget.LinearLayoutManager;
import android.support.v7.widget.RecyclerView;
import android.view.Gravity;
import android.view.View;
import android.view.ViewGroup;
import android.widget.ImageView;
import android.widget.LinearLayout;

import com.squareup.picasso.Picasso;

import java.util.ArrayList;
import java.util.List;
import java.util.Random;

public class MainActivity extends AppCompatActivity {

    private RecyclerView recyclerView;

    private Handler handler = new Handler();

    public static final int ADD_DATA_DURATION = 2000;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        initView();
    }

    private void initView(){
        recyclerView = (RecyclerView) findViewById(R.id.recyclerView);

        final RecyclerView.LayoutManager layoutManager = new GridLayoutManager(this,3);
        recyclerView.setLayoutManager(layoutManager);
        recyclerView.setHasFixedSize(true);
        RecyclerView.ItemAnimator itemAnimator = new DefaultItemAnimator();
        recyclerView.setItemAnimator(itemAnimator);

        final MyAdapter adapter = new MyAdapter();
        recyclerView.setAdapter(adapter);

        handler.postDelayed(new Runnable() {
            @Override
            public void run() {
                adapter.addData();
                handler.postDelayed(this, ADD_DATA_DURATION);
                layoutManager.scrollToPosition(adapter.getSize());
            }
        },ADD_DATA_DURATION);
    }

    private class MyAdapter extends RecyclerView.Adapter{

        private final String[] imageUrlArray = {
                "http://o6p4e1uhv.bkt.clouddn.com/tu24967_22.jpg",
                "http://o6p4e1uhv.bkt.clouddn.com/cce4b48f8c5494ee7008eb9528f5e0fe98257eca.jpg",
                "http://o6p4e1uhv.bkt.clouddn.com/tu25422_4.jpg",
                "http://o6p4e1uhv.bkt.clouddn.com/ad7fd688d43f879424026deed01b0ef41ad53a2e.jpg",
                "http://o6p4e1uhv.bkt.clouddn.com/tu25422_6.jpg",
                "http://o6p4e1uhv.bkt.clouddn.com/refsdg.jpg",
                "http://o6p4e1uhv.bkt.clouddn.com/ggfnvbn.jpg",
                "http://o6p4e1uhv.bkt.clouddn.com/sghgfsh.jpg",
                "http://o6p4e1uhv.bkt.clouddn.com/asfasdf.jpg",
                "http://o6p4e1uhv.bkt.clouddn.com/fsbgbsfg.jpg",
                "http://o6p4e1uhv.bkt.clouddn.com/gsfdtrysrtsfdg.jpg",
                "http://o6p4e1uhv.bkt.clouddn.com/sdfgsrters.jpg"};

        private List<String> datas = new ArrayList<>();

        public MyAdapter(){
        }

        public void addData(){
            Random random = new Random();
            datas.add(imageUrlArray[random.nextInt(imageUrlArray.length)]);
            notifyItemInserted(datas.size());
        }

        public int getSize(){
            return datas.size();
        }
        @Override
        public RecyclerView.ViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {

            RecyclerView.LayoutParams reLP = new RecyclerView.LayoutParams(RecyclerView.LayoutParams.MATCH_PARENT,RecyclerView.LayoutParams.WRAP_CONTENT);
            reLP.setMargins(20, 20, 20, 20);
            CardView cardView = new CardView(parent.getContext());
            cardView.setLayoutParams(reLP);

            CardView.LayoutParams cLP = new CardView.LayoutParams(parent.getMeasuredWidth()/3,(int)(parent.getMeasuredWidth()/3*1.3));
            ImageView imageView = new ImageView(parent.getContext());
            imageView.setLayoutParams(cLP);
            imageView.setScaleType(ImageView.ScaleType.FIT_XY);
            cardView.addView(imageView);

            MyHolder holder = new MyHolder(cardView);

            return holder;
        }

        @Override
        public void onBindViewHolder(RecyclerView.ViewHolder holder, int position) {
            MyHolder myHolder = (MyHolder)holder;
            ImageView imageView = myHolder.imageView;
            Picasso.with(imageView.getContext()).load(datas.get(position)).into(imageView);
        }

        @Override
        public int getItemCount() {
            return datas.size();
        }

        private class MyHolder extends RecyclerView.ViewHolder{

            public ImageView imageView ;
            public MyHolder(View itemView) {
                super(itemView);
                imageView = (ImageView) ((CardView)itemView).getChildAt(0);
            }
        }
    }
}

使用RecyclerView以下几个东西是必备的：

1. RecyclerView.LayoutManager
2. RecyclerView.Adapter
   
   其中LayoutManager负责布局，Adapter负责数据集。
   
   该demo运行结果如下：

后面我们对RecyclerView的研究就给予这个demo，demo完整源码地址：

https://github.com/ZhangQinglian/RecyclerViewAdvance