Android RecyclerView线性布局详解(1)

2019-12-12 03:36:05

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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：

这里写图片描述

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：

这里写图片描述

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：

这里写图片描述

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 }; /* orientation 方向 */ public LinearDivider(Context context, int orientation) { final TypedArray ta = context.obtainStyledAttributes(ATRRS); this.mDividerDarwable = ta.getDrawable(0); ta.recycle(); setOrientation(orientation); } /* int orientation 方向 int dividerHight 分割线的线宽 Drawable dividerDrawable 充当分割线的图片 */ public LinearDivider(Context context, int orientation, int dividerHight, Drawable dividerDrawable) { this(context, orientation); mDividerHight = dividerHight; mDividerDarwable = dividerDrawable; } /* int orientation 方向 int dividerHight 分割线的线宽 int dividerColor 分割线的颜色 */ 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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