android RecyclerView使用（一）

在项目中我们经常用到recyclerView来实现各种列表。RecyclerView相对于LIstView的优点：

1.RecyclerView封装了ViewHolder的回收复用

2.提供了一种插拔式的体验，高度的解耦，异常的灵活，针对一个Item的显示，RecyclerView专门抽取出了相应的类，来控制Item的显示，使其的扩展性非常强。

3.可以控制Item的增删动画，可以通过ItemAnimator这个类控制

下面介绍一下RecyclerVeiw的基本用法。

首先我们要gradle的依赖库中添加

 compile 'com.android.support:recyclerview-v7:26.0.0-alpha1'

在activity_main.xml中添加控件

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:id="@+id/activity_main"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
   >
    <android.support.v7.widget.RecyclerView
        android:id="@+id/rv"
        android:layout_width="match_parent"
        android:layout_height="wrap_content">
    </android.support.v7.widget.RecyclerView>
</RelativeLayout>

新建一个布局文件，作为item布局

recyclerview_item.xml

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:orientation="horizontal" android:layout_width="match_parent"
    android:layout_height="wrap_content">
    <ImageView
        android:id="@+id/iv_item"
        android:layout_width="50dp"
        android:layout_height="50dp"
        android:background="@color/colorAccent"/>
    <TextView
        android:id="@+id/tv_item"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content" 
        />
</LinearLayout>

Recyclerview的主要有四个步骤，

1.设置Adapter

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2.设置布局管理器

3.设置item分割线

4.设置item增删动画

/**
* 设置Adapter
*/
mRecyclerView.setAdapter(mListAdapter);
/**
* 设置布局管理器
*/
mRecyclerView.setLayoutManager(linearLayoutManager);
/**
* 设置item分割线
*/
mRecyclerView.addItemDecoration(itemDecoration);
/**
* 设置item动画
*/
mRecyclerView.setItemAnimator(new DefaultItemAnimator());

RecyclerView.Adapter需要实现3个方法

1.onCreateViewHolder() 用来展现视图和它的持有者

2.onBindViewHolder() 主要用来把数据绑定到视图上。

3.getItemCount() 返回item的数量

package rv.hq.com.recyclerviewdemo;

import android.content.Context;
import android.support.v7.widget.RecyclerView;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.TextView;

import java.util.List;

/**
 * Created by asus on 2018/3/27.
 */

public class MyAdapter extends RecyclerView.Adapter<MyAdapter.MyViewHolder>{
    private List<String> data;
    private Context mContext;
    private LayoutInflater mInflater;
    public MyAdapter(Context context, List<String> mData){
        this.mContext = context;
        this.data = mData;
        this.mInflater = LayoutInflater.from(context);
    }

    @Override
    public MyViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {

        View view = mInflater.inflate (R.layout.recyclerview_item,parent, false);
        MyViewHolder viewHolder = new MyViewHolder (view);
        return viewHolder;

    }

    @Override
    public void onBindViewHolder(MyViewHolder holder, int position) {
        holder.textView.setText(data.get(position));

    }

    @Override
    public int getItemCount() {
        return data.size();
    }
    class MyViewHolder extends RecyclerView.ViewHolder{
        private TextView textView;

        public MyViewHolder(View view){
            super(view);
            textView = view.findViewById(R.id.tv_item);
        }
    }
}

RecyclerView常用的布局管理器有三种：

1.LinearLayoutManager：展示了水平或者垂直的滚动列表，相当于之前学习的ListView，但是没有页眉和页尾。

2.GridLayoutManager：在网格中展示条目，相当于之前学习的GridView。

3.StaggeredGridLayoutManager：在错落的网格中展示条目，比如常见的瀑布流。

系统给我们提供了一个叫做ItemDecoration的抽象类，却并没有提供它的实现类供我们使用，所以我们必须通过自定义它去使用它，这里我就不重复造轮子啦，网上有很多现成的ItemDecoration的实现类，我们挑一个比较好用的来实现分割线效果:

package rv.hq.com.recyclerviewdemo;

import android.content.Context;
import android.content.res.TypedArray;
import android.graphics.Canvas;
import android.graphics.Rect;
import android.graphics.drawable.Drawable;
import android.support.v7.widget.LinearLayoutManager;
import android.support.v7.widget.RecyclerView;
import android.view.View;

/**
 * Created by asus on 2018/3/27.
 */

public class DividerItemDecoration extends RecyclerView.ItemDecoration{
    private static final int[] ATTRS = new int[]{
            android.R.attr.listDivider
    };

    public static final int HORIZONTAL_LIST = LinearLayoutManager.HORIZONTAL;

    public static final int VERTICAL_LIST = LinearLayoutManager.VERTICAL;

    private Drawable mDivider;

    private int mOrientation;

    public DividerItemDecoration(Context context, int orientation) {
        final TypedArray a = context.obtainStyledAttributes(ATTRS);
        mDivider = a.getDrawable(0);
        a.recycle();
        setOrientation(orientation);
    }

    public void setOrientation(int orientation) {
        if (orientation != HORIZONTAL_LIST && orientation != VERTICAL_LIST) {
            throw new IllegalArgumentException("invalid orientation");
        }
        mOrientation = orientation;
    }

    @Override
    public void onDraw(Canvas c, RecyclerView parent) {
        if (mOrientation == VERTICAL_LIST) {
            drawVertical(c, parent);
        } else {
            drawHorizontal(c, parent);
        }
    }

    public void drawVertical(Canvas c, RecyclerView parent) {
        final int left = parent.getPaddingLeft();
        final 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 + mDivider.getIntrinsicHeight();
            mDivider.setBounds(left, top, right, bottom);
            mDivider.draw(c);
        }
    }

    public void drawHorizontal(Canvas c, RecyclerView parent) {
        final int top = parent.getPaddingTop();
        final int bottom = parent.getHeight() - parent.getPaddingBottom();

        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 left = child.getRight() + params.rightMargin;
            final int right = left + mDivider.getIntrinsicHeight();
            mDivider.setBounds(left, top, right, bottom);
            mDivider.draw(c);
        }
    }

    @Override
    public void getItemOffsets(Rect outRect, int itemPosition, RecyclerView parent) {
        if (mOrientation == VERTICAL_LIST) {
            outRect.set(0, 0, 0, mDivider.getIntrinsicHeight());
        } else {
            outRect.set(0, 0, mDivider.getIntrinsicWidth(), 0);
        }
    }


}

最后在MainActivity.class里设置

package rv.hq.com.recyclerviewdemo;

import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.support.v7.widget.LinearLayoutManager;
import android.support.v7.widget.RecyclerView;

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

public class MainActivity extends AppCompatActivity {
    private RecyclerView mRecyclerView;
    private MyAdapter adapter;
    private List<String> data;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        mRecyclerView = (RecyclerView) findViewById(R.id.rv);
        initData();
        adapter = new MyAdapter(MainActivity.this,data);
        mRecyclerView.setAdapter(adapter);
        LinearLayoutManager layoutManager = new LinearLayoutManager(this);
        mRecyclerView.setLayoutManager(layoutManager);
        mRecyclerView.addItemDecoration(new DividerItemDecoration (this,
                DividerItemDecoration.VERTICAL_LIST));
    }
    private void initData(){
        data = new ArrayList<>();
        for(int i = 0;i < 6;i++){
            data.add("测试数据"+i);
        }
    }
}

最后如图效果：

在简单介绍了recyclerView的线性布局之后，我们来了解下网格布局和常见的瀑布流布局。

其实和线性布局差不多，主要是布局管理器的改变，和一些属性的使用。

一.网格布局

网格布局管理器--GridLayoutManager

只需将布局管理进行修改，就可以变成网格状了，如下：

//mRecyclerView.setLayoutManager(new LinearLayoutManager(this));
        mRecyclerView.setLayoutManager(new GridLayoutManager(this,4))

二.瀑布流式的布局

瀑布流布局管理器--StaggeredGridLayoutManager

mRecyclerView.setLayoutManager(new StaggeredGridLayoutManager(4, StaggeredGridLayoutManager.VERTICAL));

demo下载：https://download.csdn.net/download/hua93/10312269

android RecyclerView使用（一）

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