Android应用开发中RecyclerView组件使用入门教程

RecyclerView是一种列表容器, 发布很久了, 才想起来写点什么.

RecyclerView相比于ListView, 在回收重用时更具有灵活性, 也就是低耦合, 并且提供了扩展. 加载多个视图时, 应该多用RecyclerView代替ListView.

那么我们来看看这东西应该怎么用? 比如生成一个瀑布流的视图.

首先我们从一个HelloWorld写起, 看看如何构建一个RecyclerView.

1. 依赖库
Gradle配置, 添加Recycler库

compile 'com.android.support:recyclerview-v7:+'

2. 资源文件
资源文件

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

3. 代码
LayoutManager: 管理RecyclerView的结构.
Adapter: 处理每个Item的显示.
ItemDecoration: 添加每个Item的装饰.
ItemAnimator: 负责添加\移除\重排序时的动画效果.

LayoutManager\Adapter是必须, ItemDecoration\ItemAnimator是可选.
 
 private void initRecyclerView(RecyclerView recyclerView) {
  recyclerView.setHasFixedSize(true); // 设置固定大小
  initRecyclerLayoutManager(recyclerView); // 初始化布局
  initRecyclerAdapter(recyclerView); // 初始化适配器
  initItemDecoration(recyclerView); // 初始化装饰
  initItemAnimator(recyclerView); // 初始化动画效果
 }

4. LayoutManager
管理RecyclerView的布局结构.

 private void initRecyclerLayoutManager(RecyclerView recyclerView) {
  // 错列网格布局
  recyclerView.setLayoutManager(new StaggeredGridLayoutManager(4,
    StaggeredGridLayoutManager.VERTICAL));
 }

提供了多种LayoutManager, 瀑布流使用错列网格布局.
5. Adapter
适配器, 处理RecyclerView的Item事务.

 private void initRecyclerAdapter(RecyclerView recyclerView) {
  mAdapter = new MyAdapter(getData());
  recyclerView.setAdapter(mAdapter);
 }

对于Adapter, 我们需要展开来说, 先看看类.

public class MyAdapter extends RecyclerView.Adapter<MyViewHolder> {
 private List<DataModel> mDataModels;
 private List<Integer> mHeights;
 MyAdapter(List<DataModel> dataModels) {
  if (dataModels == null) {
   throw new IllegalArgumentException("DataModel must not be null");
  }
  mDataModels = dataModels;
  mHeights = new ArrayList<>();
 }
 @Override
 public MyViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
  View itemView = LayoutInflater.from(parent.getContext())
    .inflate(R.layout.item_recycler_view, parent, false);
  return new MyViewHolder(itemView);
 }
 @Override
 public void onBindViewHolder(MyViewHolder holder, int position) {
  DataModel dataModel = mDataModels.get(position);
  // 随机高度, 模拟瀑布效果.
  if (mHeights.size() <= position) {
   mHeights.add((int) (100 + Math.random() * 300));
  }
  ViewGroup.LayoutParams lp = holder.getTvLabel().getLayoutParams();
  lp.height = mHeights.get(position);
  holder.getTvLabel().setLayoutParams(lp);
  holder.getTvLabel().setText(dataModel.getLabel());
  holder.getTvDateTime().setText(new SimpleDateFormat("yyyy-MM-dd", Locale.ENGLISH)
    .format(dataModel.getDateTime()));
 }
 @Override
 public int getItemCount() {
  return mDataModels.size();
 }
 public void addData(int position) {
  DataModel model = new DataModel();
  model.setDateTime(getBeforeDay(new Date(), position));
  model.setLabel("No. " + (int) (new Random().nextDouble() * 20.0f));
  mDataModels.add(position, model);
  notifyItemInserted(position);
 }
 public void removeData(int position) {
  mDataModels.remove(position);
  notifyItemRemoved(position);
 }
 
 private static Date getBeforeDay(Date date, int i) {
  Calendar calendar = Calendar.getInstance();
  calendar.setTime(date);
  calendar.add(Calendar.DAY_OF_YEAR, i * (-1));
  return calendar.getTime();
 }
}

（1）onCreateViewHolder创建ViewHolder.

（2）onBindViewHolder绑定每一项数据.

（3）getItemCount返回列表长度.

（4）RecyclerView强制使用ViewHolder.

public class MyViewHolder extends RecyclerView.ViewHolder {
 private TextView mTvLabel; // 标签
 private TextView mTvDateTime; // 日期
 public MyViewHolder(View itemView) {
  super(itemView);
  mTvLabel = (TextView) itemView.findViewById(R.id.item_text);
  mTvDateTime = (TextView) itemView.findViewById(R.id.item_date);
 }
 public TextView getTvLabel() {
  return mTvLabel;
 }
 public TextView getTvDateTime() {
  return mTvDateTime;
 }
}

在onCreateViewHolder方法, 创建类; 在onBindViewHolder方法, 绑定数据.
DataModel

public class DataModel {
 private String mLabel;
 private Date mDateTime;
 public String getLabel() {
  return mLabel;
 }
 public void setLabel(String label) {
  mLabel = label;
 }
 public Date getDateTime() {
  return mDateTime;
 }
 public void setDateTime(Date dateTime) {
  mDateTime = dateTime;
 }
}

6. ItemDecoration
项的装饰, 比如ListView中的分割线, 在本例中, 左右两条粉线.

 private void initItemDecoration(RecyclerView recyclerView) {
  recyclerView.addItemDecoration(new MyItemDecoration(this));
 }

ItemDecoration, 注意parent和child的使用方式.

public class MyItemDecoration extends RecyclerView.ItemDecoration {
 private static final int[] ATTRS = new int[]{android.R.attr.listDivider};
 private Drawable mDivider;
 public MyItemDecoration(Context context) {
  final TypedArray array = context.obtainStyledAttributes(ATTRS);
  mDivider = array.getDrawable(0);
  array.recycle();
 }
 @Override
 public void onDraw(Canvas c, RecyclerView parent, State state) {
  drawHorizontal(c, parent);
  drawVertical(c, parent);
 }
 // 水平线
 public void drawHorizontal(Canvas c, RecyclerView parent) {
  final int childCount = parent.getChildCount();
  // 在每一个子控件的底部画线
  for (int i = 0; i < childCount; i++) {
   final View child = parent.getChildAt(i);
   final int left = child.getLeft() + child.getPaddingLeft();
   final int right = child.getWidth() + child.getLeft() - child.getPaddingRight();
   final int top = child.getBottom() - mDivider.getIntrinsicHeight() - child.getPaddingBottom();
   final int bottom = top + mDivider.getIntrinsicHeight();
   mDivider.setBounds(left, top, right, bottom);
   mDivider.draw(c);
  }
 }
 // 竖直线
 public void drawVertical(Canvas c, RecyclerView parent) {
  final int childCount = parent.getChildCount();
  // 在每一个子控件的右侧画线
  for (int i = 0; i < childCount; i++) {
   final View child = parent.getChildAt(i);
   int right = child.getRight() - child.getPaddingRight();
   int left = right - mDivider.getIntrinsicWidth();
   final int top = child.getTop() + child.getPaddingTop();
   final int bottom = child.getTop() + child.getHeight() - child.getPaddingBottom();
   mDivider.setBounds(left, top, right, bottom);
   mDivider.draw(c);
  }
 }
 // Item之间的留白
 @Override
 public void getItemOffsets(Rect outRect, View view, RecyclerView parent, State state) {
  outRect.set(0, 0, mDivider.getIntrinsicWidth(), mDivider.getIntrinsicHeight());
 }
}

本例重写了listDivider

 <style name="AppTheme" parent="Theme.AppCompat.Light.DarkActionBar">
  ...
  <item name="android:listDivider">@drawable/divider_bg</item>
 </style>
<?xml version="1.0" encoding="utf-8"?>
<shape xmlns:android="http://schemas.android.com/apk/res/android"
  android:shape="rectangle">
 <solid android:color="#ff00ff"/>
 <size android:height="4dp"/>
 <size android:width="4dp"/>
</shape>

7. ItemAnimator
动画效果比较复杂, 使用默认动画. 如要定制的话, 继承DefaultItemAnimator; 如设置null, 则不显示任何动画.

 private void initItemAnimator(RecyclerView recyclerView) {
  recyclerView.setItemAnimator(new DefaultItemAnimator()); // 默认动画
 }

8. 最终Activity

public class MainActivity extends AppCompatActivity {
 private MyAdapter mAdapter;
 @Override
 protected void onCreate(Bundle savedInstanceState) {
  super.onCreate(savedInstanceState);
  setContentView(R.layout.activity_main);
  Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
  setSupportActionBar(toolbar);
  FloatingActionButton fab = (FloatingActionButton) findViewById(R.id.fab);
  fab.setOnClickListener(new View.OnClickListener() {
   @Override
   public void onClick(View view) {
    Snackbar.make(view, "Replace with your own action", Snackbar.LENGTH_LONG)
      .setAction("Action", null).show();
   }
  });
  // 初始化RecyclerView
  initRecyclerView((RecyclerView) findViewById(R.id.test_recycler_view));
 }
 
 private void initRecyclerView(RecyclerView recyclerView) {
  recyclerView.setHasFixedSize(true); // 设置固定大小
  initRecyclerLayoutManager(recyclerView); // 初始化LayoutManager
  initRecyclerAdapter(recyclerView); // 初始化Adapter
  initItemDecoration(recyclerView); // 初始化边界装饰
  initItemAnimator(recyclerView); // 初始化动画效果
 }
 
 private void initRecyclerLayoutManager(RecyclerView recyclerView) {
  // 错列网格布局
  recyclerView.setLayoutManager(new StaggeredGridLayoutManager(4,
    StaggeredGridLayoutManager.VERTICAL));
 }
 
 private void initRecyclerAdapter(RecyclerView recyclerView) {
  mAdapter = new MyAdapter(getData());
  recyclerView.setAdapter(mAdapter);
 }
 
 private void initItemDecoration(RecyclerView recyclerView) {
  recyclerView.addItemDecoration(new MyItemDecoration(this));
 }
 
 private void initItemAnimator(RecyclerView recyclerView) {
  recyclerView.setItemAnimator(new DefaultItemAnimator()); // 默认动画
 }
 
 private ArrayList<DataModel> getData() {
  int count = 57;
  ArrayList<DataModel> data = new ArrayList<>();
  for (int i = 0; i < count; i++) {
   DataModel model = new DataModel();
   model.setDateTime(getBeforeDay(new Date(), i));
   model.setLabel("No. " + i);
   data.add(model);
  }
  return data;
 }
 
 private static Date getBeforeDay(Date date, int i) {
  Calendar calendar = Calendar.getInstance();
  calendar.setTime(date);
  calendar.add(Calendar.DAY_OF_YEAR, i * (-1));
  return calendar.getTime();
 }
 @Override
 public boolean onCreateOptionsMenu(Menu menu) {
  // Inflate the menu; this adds items to the action bar if it is present.
  getMenuInflater().inflate(R.menu.menu_main, menu);
  return true;
 }
 @Override
 public boolean onOptionsItemSelected(MenuItem item) {
  // Handle action bar item clicks here. The action bar will
  // automatically handle clicks on the Home/Up button, so long
  // as you specify a parent activity in AndroidManifest.xml.
  int id = item.getItemId();
  switch (item.getItemId()) {
   case R.id.id_action_add:
    mAdapter.addData(1);
    break;
   case R.id.id_action_delete:
    mAdapter.removeData(1);
    break;
  }
  //noinspection SimplifiableIfStatement
  if (id == R.id.action_settings) {
   return true;
  }
  return super.onOptionsItemSelected(item);
 }
}

为了测试动画, Menu额外添加两个按钮。

9.运行ReactNative示例
既然感觉ReactNative开发靠谱, 那么我们就来看看ReactNative都能做哪些好玩的东西, 和原生的有哪些区别?
示例图

按照文档安装一些命令行工具, 再下载Git代码.
Github: https://github.com/facebook/react-native

内容很多, 包含一些依赖库和示例(Example), 下载的有点慢, 耐心等待.

下载完成后, 在react-native内, 执行npm install.

Android项目执行, 参考ReactAndroid的README.md.

在react-native目录, 新建local.properties

sdk.dir=/Users/wangchenlong/Installations/android-sdk
ndk.dir=/Users/wangchenlong/Installations/android-ndk-r10e

执行

cd react-native
./gradlew :ReactAndroid:assembleDebug

再执行

./gradlew :ReactAndroid:installArchives

启动服务

./packager/packager.sh

安装项目

cd react-native
./gradlew :Examples:UIExplorer:android:app:installDebug

一定要先启动服务, 再安装项目.
出现transforming 100%, 即导入成功.

在最新版本中, 我的红米note4无法运行项目.
报错: Upload package to device fails.
原因是编译的gradle版本太高, 默认1.5.0, 实际1.2.0~1.3.0都可以运行.
我的是1.2.3.
真机调试, 本人红米note(Android 4.2)
摇动手机, 选择Dev Settings->Debug sever host & port for device. 设置IP地址, 观察本机的IP, 填入即可. 我当前的是

192.168.2.202:8081
注意设置端口8081, 否则无法加载. 有些情况可以直接输入IP即可.
Android5.0以上, 直接设置端口即可.

adb reverse tcp:8081 tcp:8081

参考Android的真机调试文档.

IOS模拟器, 太穷没有iPhone. 直接打开open UIExplorer.xcodeproj项目, 执行就可以显示.

开发有两种选择, 一种是直接基于ReactNative开发, 一种是把ReactNative集成到现有的App中, 对于第二种, 我们就需要关注, ReactNative会增大多少代码呢?

使用最基本的HelloWorld做测试, ReactNative也是生成一个简单HelloWorld的JS. 最新生成的HelloWorld的大小是1.4M, 加上ReactNative的是7.6M, 框架大约6.2M左右, 各位可以权衡一下使用.

ReactNative的UIExplorer已经包含了大量示例, 很接近原生, 非常绚丽, 速度也很快. 如Android的ViewPager

OK, 好的开始是成功的一半, 继续探索吧! Enjoy it!

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