Android RecyclerView线性布局详解(1)

RecyclerView是Android 5.0新增的控件，在android-support-v7下面。官方文档对RecycleView介绍很简洁到位，如下：

A flexible view for providing a limited window into a large data set.
大概意思就是说：在有限大小的窗口里显示大量数据的一个灵活的view。

下面是ReccleView继承图：

看到这里我们自然想到了与之类似的控件ListView，RecyclerView和ListView都是在有限的屏幕区域里维护少量的View来进行显示大量的数据，其实RecyclerView是ListView的升级版，功能更加强大，更加灵活，扩展性更强，Google建议使用RecycleView替代ListView。

下面是RecycleView结构图：

RecycleView主要包括以下几个部件：

1. RecyclerView.Adapter

数据和视图的分离设计是程序解耦和可维护的重要指标，RecycleView作为展示大量数据的view肯定是遵循这个设计的，ListView也不例外。通过继承RecycleView.Adapter即可轻松实现自己的adapter，主要重写RecycleView.Adapter的下面三个方法即可实现：

public MyRecycleViewAdapter.MyViewHolder onCreateViewHolder(ViewGroup parent, int viewType) 
public void onBindViewHolder(MyRecycleViewAdapter.MyViewHolder holder, int position)
public int getItemCount() 

上面MyRecycleViewAdapter是我自己定义的ViewHolder

2. ViewHolder

ViewHolder用来保存列表中item view引用的类，这样做的目的是重用item视图，从而提高性能。
在ListView中，ViewHolder不是ListView自带的，是需要自己定义的，当然你也可以不使用ViewHolder，这样的后果就是ListView每次调用getView()方法的时候都会调用findViewById()方法，要知道findViewById()性能很差，它通过递归的方式去从view树中找特定的子view的，最终往往带来很差的性能体验，所以使用ViewHolder也成了优化ListView最重要的手段。
在RecyclerView中，Android内置了RecyclerView.ViewHolder，这意味着ViewHolder使用成了必须。

3. 分割线 RecycleView.ItemDecoration

ListView添加分割线很简单，只需在ListView的xml中配置”divider”属性即可，如：

android:dividerHeight="2dp"
android:divider="@color/red"

但RecycleView添加分割线是比较麻烦的，并且默认是不带分割线的。但实际开发中一般都需要分割线，使用RecycleView.ItemDecoration为RecycleView添加分割线

4. 布局管理器 LayoutManager

RecycleView支持多种布局模式：

1、LinearLayoutManager
线性布局管理器，支持水平布局和垂直布局两种
2、GridLayoutManager
网格布局管理器
3、StaggerdGridLayoutManager
错列的网格布局管理器，可以实现瀑布流列表

RecycleView使用时和ListView很类似，直接看一个简单的例子，分别展示一个垂直方向和水平方向上的列表，并且都支持使用颜色和图片做分割线，效果图如下：

1. MainActivity

package com.cjl.recycleviewtest;
...
public class MainActivity extends AppCompatActivity {
 private VerticalFragment mVerticalFragment;
 private HorizontalFragment mHorizontalFragment;
 @Override
 protected void onCreate(Bundle savedInstanceState) {
 super.onCreate(savedInstanceState);
 setContentView(R.layout.activity_main);
 //垂直
 mVerticalFragment = new VerticalFragment();
 //水平
 mHorizontalFragment = new HorizontalFragment();
 //默认为设置垂直
 getFragmentManager().beginTransaction().replace(R.id.activity_main, mVerticalFragment).commit();
 }
 @Override
 public boolean onCreateOptionsMenu(Menu menu) {
 MenuInflater inflater = getMenuInflater();
 inflater.inflate(R.menu.menu_recycleview, menu);
 return super.onCreateOptionsMenu(menu);
 }
 @Override
 public boolean onOptionsItemSelected(MenuItem item) {
 int id = item.getItemId();
 switch (id) {
  //垂直方向
  case R.id.vertical:
  VerticalFragment mVerticalFragment = new VerticalFragment();
  getFragmentManager().beginTransaction().replace(R.id.activity_main, mVerticalFragment).commit();
  break;
  //水平方向
  case R.id.horizontal:
 getFragmentManager().beginTransaction().replace(R.id.activity_main, mHorizontalFragment).commit();
  break;
 }
 return super.onOptionsItemSelected(item);
 }
}

MainActivity布局文件 R.layout.activity_main

<?xml version="1.0" encoding="utf-8"?>
<FrameLayout xmlns:android="Http://schemas.android.com/apk/res/android"
 android:id="@+id/activity_main"
 android:layout_width="match_parent"
 android:layout_height="match_parent">
</FrameLayout>

2. 垂直方向上 VerticalFragment

public class VerticalFragment extends Fragment implements View.OnClickListener{
 private RecyclerView mRecycleViewDrawable;
 private RecyclerView mRecycleViewColor;
 private LinearLayoutManager mManagerColor;
 private LinearLayoutManager mManagerDrawable;
 private List<String> mData;
 private Button mDrawable;
 private Button mColor;
 private MyRecycleViewAdapter mRecycleViewAdapter;
 @Nullable
 @Override
 public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
 View view = inflater.inflate(R.layout.fragment_vertical_layout, container, false);
 mRecycleViewDrawable = (RecyclerView) view.findViewById(R.id.recycleview_drawable);
 mRecycleViewColor = (RecyclerView) view.findViewById(R.id.recycleview_color);
 mDrawable = (Button) view.findViewById(R.id.btn_drawable);
 mDrawable.setOnClickListener(this);
 mColor = (Button) view.findViewById(R.id.btn_color);
 mColor.setOnClickListener(this);
 //1. 颜色分割线
 mManagerColor = new LinearLayoutManager(getActivity());
 mManagerColor.setOrientation(LinearLayoutManager.VERTICAL);
 mRecycleViewColor.setLayoutManager(mManagerColor);
 //设置颜色分割线
 mRecycleViewColor.addItemDecoration(new LinearDivider(getActivity(), LinearLayoutManager.VERTICAL, 10, this.getResources().getColor(R.color.colorAccent)));
 //2. 图片分割线
 mManagerDrawable = new LinearLayoutManager(getActivity());
 mManagerDrawable.setOrientation(LinearLayoutManager.VERTICAL);
 mRecycleViewDrawable.setLayoutManager(mManagerDrawable);
 //设置图片分割线
 Drawable drawable = ContextCompat.getDrawable(getActivity(), R.mipmap.divider);
 mRecycleViewDrawable.addItemDecoration(new LinearDivider(getActivity(), LinearLayoutManager.VERTICAL, 20, drawable));
 mData = new ArrayList<String>();
 initData(mData);
 //自定义adapter
 mRecycleViewAdapter = new MyRecycleViewAdapter(getActivity(), R.layout.item_vertical_recycleview, mData);
 //设置adapter
 mRecycleViewColor.setAdapter(mRecycleViewAdapter);
 mRecycleViewDrawable.setAdapter(mRecycleViewAdapter);
 return view;
 }
 private void initData(List<String> dataList) {
 for (int i = 0; i < 30; i++) {
  dataList.add("item" + i);
 }
 }
 @Override
 public void onClick(View view) {
 int id = view.getId();
 switch (id){
  case R.id.btn_drawable:
  mRecycleViewColor.setVisibility(View.INVISIBLE);
  mRecycleViewDrawable.setVisibility(View.VISIBLE);
  break;
  case R.id.btn_color:
  mRecycleViewColor.setVisibility(View.VISIBLE);
  mRecycleViewDrawable.setVisibility(View.INVISIBLE);
  break;
 }
 }
}

VerticalFragment 的布局文件 R.layout.fragment_vertical_layout

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
 android:layout_width="match_parent"
 android:layout_height="match_parent">
 <android.support.v7.widget.RecyclerView
 android:id="@+id/recycleview_drawable"
 android:layout_width="match_parent"
 android:layout_height="match_parent"
 android:layout_marginBottom="60dp"/>
 <android.support.v7.widget.RecyclerView
 android:id="@+id/recycleview_color"
 android:layout_width="match_parent"
 android:layout_height="match_parent"
 android:layout_marginBottom="60dp"
 android:visibility="invisible"/>
 <LinearLayout
 android:id="@+id/lilayout"
 android:orientation="horizontal"
 android:layout_width="match_parent"
 android:layout_height="wrap_content"
 android:weightSum="2"
 android:layout_alignParentBottom="true">
 <Button
  android:id="@+id/btn_drawable"
  android:layout_width="wrap_content"
  android:layout_height="50dp"
  android:text="图片分割线"
  android:gravity="center"
  android:layout_weight="1"
  android:background="@color/colorPrimary"/>
 <Button
  android:id="@+id/btn_color"
  android:layout_width="wrap_content"
  android:layout_height="50dp"
  android:text="颜色分割线"
  android:gravity="center"
  android:layout_weight="1"
  android:background="@color/mytv"/>
 </LinearLayout>
</RelativeLayout>

3. 直接继承RecyclerView.Adapter

public class MyRecycleViewAdapter extends RecyclerView.Adapter<MyRecycleViewAdapter.MyViewHolder> {
 private LayoutInflater mLayoutInflater;
 private List<String> mDataList;
 private int mItemLayout;
 public MyRecycleViewAdapter(Context context, int itemLayout, List<String> datalist) {
 mLayoutInflater = LayoutInflater.from(context);
 mItemLayout = itemLayout;
 mDataList = datalist;
 }
 @Override
 public MyRecycleViewAdapter.MyViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
 return new MyViewHolder(mLayoutInflater.inflate(mItemLayout, parent, false));
 }
 @Override
 public void onBindViewHolder(MyRecycleViewAdapter.MyViewHolder holder, int position) {
 holder.mTextView.setText(mDataList.get(position));
 }
 @Override
 public int getItemCount() {
 return mDataList.size();
 }
 class MyViewHolder extends RecyclerView.ViewHolder {
 private TextView mTextView;
 public MyViewHolder(View itemView) {
  super(itemView);
  mTextView = (TextView) itemView.findViewById(R.id.tv);
 }
 }
}

item布局文件 item_vertical_recycleview.xml

<?xml version="1.0" encoding="utf-8"?>
<FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"
 android:layout_width="match_parent"
 android:layout_height="wrap_content">
 <TextView
 android:id="@+id/tv"
 android:gravity="center"
 android:layout_width="match_parent"
 android:layout_height="60dp"/>
</FrameLayout>

4. 分割线 RecyclerView.ItemDecoration

public class LinearDivider extends RecyclerView.ItemDecoration {
 private Drawable mDividerDarwable;
 private int mOrientation;
 private int mDividerHight = 1;
 private Paint mColorPaint;
 public final int[] ATRRS = new int[]{
  android.R.attr.listDivider
 };
 
 public LinearDivider(Context context, int orientation) {
 final TypedArray ta = context.obtainStyledAttributes(ATRRS);
 this.mDividerDarwable = ta.getDrawable(0);
 ta.recycle();
 setOrientation(orientation);
 }
 
 public LinearDivider(Context context, int orientation, int dividerHight, Drawable dividerDrawable) {
 this(context, orientation);
 mDividerHight = dividerHight;
 mDividerDarwable = dividerDrawable;
 }
 
 public LinearDivider(Context context, int orientation, int dividerHight, int dividerColor) {
 this(context, orientation);
 mDividerHight = dividerHight;
 mColorPaint = new Paint();
 mColorPaint.setColor(dividerColor);
 }
 public void setOrientation(int orientation) {
 if (orientation != LinearLayoutManager.HORIZONTAL && orientation != LinearLayoutManager.VERTICAL) {
  throw new IllegalArgumentException("方向参数错误！");
 }
 mOrientation = orientation;
 }
 @Override
 public void onDraw(canvas c, RecyclerView parent, RecyclerView.State state) {
 super.onDraw(c, parent, state);
 if (mOrientation == LinearLayoutManager.HORIZONTAL) {
  drawHorizontalDivider(c, parent);
 } else {
  drawVirticalDivider(c, parent);
 }
 }
 //画垂直分割线
 public void drawVirticalDivider(Canvas c, RecyclerView parent) {
 int left = parent.getPaddingLeft();
 int right = parent.getWidth() - parent.getPaddingRight();
 final int childCount = parent.getChildCount();
 for (int i = 0; i < childCount; i++) {
  final View child = parent.getChildAt(i);
  final RecyclerView.LayoutParams params = (RecyclerView.LayoutParams) child.getLayoutParams();
  final int top = child.getBottom() + params.bottomMargin;
  final int bottom = top + mDividerHight;
  if (mDividerDarwable != null) {
  mDividerDarwable.setBounds(left, top, right, bottom);
  mDividerDarwable.draw(c);
  }
  if (mColorPaint != null) {
  c.drawRect(left, top, right, bottom, mColorPaint);
  }
 }
 }
 //画水平分割线
 public void drawHorizontalDivider(Canvas c, RecyclerView parent) {
 int top = parent.getPaddingTop();
 int bottom = parent.getHeight() - parent.getPaddingBottom();
 final int childCount = parent.getChildCount();
 for (int i = 0; i < childCount; i++) {
  final View child = parent.getChildAt(i);
  RecyclerView.LayoutParams params = (RecyclerView.LayoutParams) child.getLayoutParams();
  final int left = child.getRight() + params.rightMargin;
  final int right = left + mDividerHight;
  if (mDividerDarwable != null) {
  mDividerDarwable.setBounds(left, top, right, bottom);
  mDividerDarwable.draw(c);
  }
  if (mColorPaint != null) {
  c.drawRect(left, top, right, bottom, mColorPaint);
  }
 }
 }
 @Override
 public void getItemOffsets(Rect outRect, View view, RecyclerView parent, RecyclerView.State state) {
 super.getItemOffsets(outRect, view, parent, state);
 if (mOrientation == LinearLayoutManager.HORIZONTAL) {
  outRect.set(0, 0, 0, mDividerHight);
 } else {
  outRect.set(0, 0, mDividerHight, 0);
 }
 }
}

未完待续……

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