Android RecyclerView 详解(1)---线性布局

来源：互联网发布：flashcs4软件下载编辑：程序博客网时间：2024/05/21 22:25

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：

LinearLayoutManager
线性布局管理器，支持水平布局和垂直布局两种
GridLayoutManager
网格布局管理器
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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