RecyclerView 的简单使用

最新推荐文章于 2025-01-08 09:50:15 发布

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最新推荐文章于 2025-01-08 09:50:15 发布

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本文深入探讨了RecyclerView的性能优化技术，包括ViewHolder机制的应用，以及如何在Android6.0环境下实现流畅的瀑布流布局。通过自定义分割线与监听事件的巧妙结合，展示了动态瀑布流布局的实现过程。

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RecyclerView是经典的ListView的进化与升华，它比ListView更加灵活(在android5.0 以后会逐步替代 ListView),但也因此引入了一定的复杂性。

我们知道，ListView通过使用ViewHolder来提升性能（ListView 的二级优化）。ViewHolder通过保存item中使用到的控件的引用来减少findViewById的调用，以此使ListView滑动得更加顺畅。但这种模式即使不使用也无妨。

同ListView一样，RecyclerView也需要使用Adapter。Adapter的作用主要是负责一个item中视图的布局以及信息的展示。

</pre><pre name="code" class="java">使用开发工具为 AndroidStudio ，在genymotion模拟器上运行，版本为android 6.0。 在 build.gradle 中进行如下图所示的配置（红色框部分）：

所需的布局文件：content_main.xml ：

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:paddingLeft="@dimen/activity_horizontal_margin"
    android:paddingRight="@dimen/activity_horizontal_margin"
    android:paddingTop="@dimen/activity_vertical_margin"
    android:paddingBottom="@dimen/activity_vertical_margin"
    tools:context=".MainActivity">

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

</RelativeLayout>

布局文件 home_item.xml ：

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="72dp"
    android:layout_margin="5dp"
    android:background="#9ffff0">

    <TextView
        android:id="@+id/tv_num"
        android:layout_width="100dp"
        android:layout_height="wrap_content"
        android:layout_gravity="center"
        android:gravity="center"/>

</LinearLayout>

布局文件 staggered_item.xml ：

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:layout_margin="5dp"
    android:background="#9ffff0">

    <TextView
        android:id="@+id/tv_stagger"
        android:layout_width="100dp"
        android:layout_height="wrap_content"
        android:layout_gravity="center"
        android:gravity="center"/>

</LinearLayout>

自定义分割线需要在 styles.xml 中(主题)，如果使用分割线，则不能实现动态图中的最后一个“ 瀑布流”。把 MainActivity 中adapter监听及重载方法注释掉（当然这样有些类就没有其作用），可看到如下图所示：

如下就是没有使用分割线，得到的动态图：

MainActivity 类：

package com.crazy.crazyanti;

import android.app.Activity;
import android.content.Context;
import android.content.Intent;
import android.graphics.drawable.Drawable;
import android.os.Bundle;
import android.support.v4.content.ContextCompat;
import android.support.v7.widget.GridLayoutManager;
import android.support.v7.widget.LinearLayoutManager;
import android.support.v7.widget.RecyclerView;
import android.support.v7.widget.StaggeredGridLayoutManager;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.widget.Toast;

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

public class MainActivity extends Activity {

    private RecyclerView mRecyclerView;

    private List<String> mDatas;

    private MyAdapter adapter;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.content_main);

        mRecyclerView = (RecyclerView) findViewById(R.id.rv_Info);

        // 设置布局容器
        LinearLayoutManager layoutManager = new LinearLayoutManager(this);
        mRecyclerView.setLayoutManager(layoutManager);

        // 初始化数据
        initData();

        // 适配器
        adapter = new MyAdapter(this, mDatas);
        mRecyclerView.setAdapter(adapter);

        // 添加分割线（为了实现动态图的效果，此处不能添加分割线，分割线在 github 上下载）
      //  mRecyclerView.addItemDecoration(new DividerItemDecoration(this, LinearLayoutManager.VERTICAL));
        // 设置监听
        adapter.setmOnItemClickListener(new MyAdapter.OnItemClickListener() {
            @Override
            public void onItemClick(View view, int position) {
                Toast.makeText(MainActivity.this, "position" + position + "Click", Toast.LENGTH_SHORT).show();
            }

            @Override
            public void onItemLongClick(View view, int position) {
                Toast.makeText(MainActivity.this, "position" + position + "Long Click", Toast.LENGTH_SHORT).show();
            }
        });
    }

    private void initData() {
        mDatas = new ArrayList<>();
        for (int i = 'A'; i <= 'z'; i++){
            mDatas.add("" + (char)i);
        }
    }

    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        getMenuInflater().inflate(R.menu.menu_main, menu);
        return true;
    }

    @Override
    public boolean onOptionsItemSelected(MenuItem item) {
        int id = item.getItemId();
        switch (id){
            case R.id.action_GridView:
                mRecyclerView.setLayoutManager(new GridLayoutManager(this, 4));
                break;
            case R.id.action_ListView:
                mRecyclerView.setLayoutManager(new LinearLayoutManager(this));
                break;
            case R.id.action_HorizontalGridView:
                mRecyclerView.setLayoutManager(new StaggeredGridLayoutManager(4,
                        StaggeredGridLayoutManager.HORIZONTAL));
                break;
            case R.id.action_StaggeredGridView:
                Intent intent = new Intent(this, StaggeredActivity.class);
                startActivity(intent);
                break;
        }
        return true;
    }
}

</pre><p></p><p></p><p>DividerItemDecoration  类为 github 上下载的开源框架：</p><p></p><pre name="code" class="java">

package com.crazy.crazyanti;


/*
 * Copyright (C) 2014 The Android Open Source Project
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * limitations under the License.
 */

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;


/**
 * This class is from the v7 samples of the Android SDK. It's not by me!
 * <p/>
 * See the license above for details.
 */
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) {
//        Log.v("recyclerview - itemdecoration", "onDraw()");

        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);
            android.support.v7.widget.RecyclerView v = new android.support.v7.widget.RecyclerView(parent.getContext());
            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);
        }
    }
}

MyAdapter 类：

package com.crazy.crazyanti;

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

import java.util.List;

public class MyAdapter extends RecyclerView.Adapter<MyAdapter.CrazyViewHolder> {

    private List<String> mDatas;

    private LayoutInflater inflater;

    public MyAdapter(Context context, List<String> mDatas){

        inflater = LayoutInflater.from(context);
        this.mDatas = mDatas;
    }

    // 设置监听接口
    public interface OnItemClickListener{
        void onItemClick(View view, int position);
        void onItemLongClick(View view, int position);
    }

    private OnItemClickListener mOnItemClickListener;

    public void setmOnItemClickListener(OnItemClickListener mOnItemClickListener){
        this.mOnItemClickListener = mOnItemClickListener;
    }

    // 创建 ViewHolder
    @Override
    public CrazyViewHolder onCreateViewHolder(ViewGroup viewGroup, int i) {
        View v = inflater.inflate(R.layout.home_item, viewGroup, false);
        return new CrazyViewHolder(v);
    }
    // 把数目绑定到条目上
    @Override
    public void onBindViewHolder(CrazyViewHolder crazyViewHolder, final int i) {
        String num = mDatas.get(i);
        crazyViewHolder.tvNum.setText(num);

        // 如果用户设置了回调，则设置点击事件
        if (mOnItemClickListener != null){

            crazyViewHolder.tvNum.setOnClickListener(new View.OnClickListener() {
                @Override
                public void onClick(View v) {
                    mOnItemClickListener.onItemClick(v, i);
                }
            });

            crazyViewHolder.tvNum.setOnLongClickListener(new View.OnLongClickListener() {
                @Override
                public boolean onLongClick(View v) {
                    mOnItemClickListener.onItemLongClick(v, i);
                    return false;
                }
            });
        }
    }

    @Override
    public int getItemCount() {
        return mDatas.size();
    }

    public class CrazyViewHolder extends RecyclerView.ViewHolder{

        TextView tvNum;

        public CrazyViewHolder(View itemView) {
            super(itemView);
            tvNum = (TextView)itemView.findViewById(R.id.tv_num);
        }
    }
}

StaggeredActivity 类：

package com.crazy.crazyanti;

import android.app.Activity;
import android.os.Bundle;
import android.support.v7.widget.GridLayoutManager;
import android.support.v7.widget.LinearLayoutManager;
import android.support.v7.widget.RecyclerView;
import android.support.v7.widget.StaggeredGridLayoutManager;
import android.view.Menu;
import android.view.MenuItem;

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

public class StaggeredActivity extends Activity {

    private RecyclerView mRecyclerView;

    private List<String> mDatas;

    private StaggeredAdapter adapter;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.content_main);

        mRecyclerView = (RecyclerView) findViewById(R.id.rv_Info);

        // 设置布局容器
        mRecyclerView.setLayoutManager(new StaggeredGridLayoutManager(3,
                StaggeredGridLayoutManager.VERTICAL));

        // 初始化数据
        initData();

        // 适配器
        adapter = new StaggeredAdapter(this, mDatas);
        mRecyclerView.setAdapter(adapter);

        // 添加分割线
      //  mRecyclerView.addItemDecoration(new DividerItemDecoration(this, LinearLayoutManager.VERTICAL));
    }

    private void initData() {
        mDatas = new ArrayList<>();
        for (int i = 'A'; i <= 'z'; i++){
            mDatas.add("" + (char)i);
        }
    }

    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        getMenuInflater().inflate(R.menu.menu_main, menu);
        return true;
    }

    @Override
    public boolean onOptionsItemSelected(MenuItem item) {
        int id = item.getItemId();
        switch (id){
            case R.id.action_GridView:
                mRecyclerView.setLayoutManager(new GridLayoutManager(this, 4));
                break;
            case R.id.action_ListView:
                mRecyclerView.setLayoutManager(new LinearLayoutManager(this));
                break;
            case R.id.action_HorizontalGridView:
                mRecyclerView.setLayoutManager(new StaggeredGridLayoutManager(4,
                        StaggeredGridLayoutManager.HORIZONTAL));
                break;
            case R.id.action_StaggeredGridView:

                break;
        }
        return true;
    }
}

StaggeredAdapter 类：

package com.crazy.crazyanti;

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

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

public class StaggeredAdapter extends Adapter<StaggeredAdapter.CrazyViewHolder> {

    private List<String> mDatas;

    private LayoutInflater inflater;
    // 每一个 item 的高度
    private List<Integer> mHeights;

    public StaggeredAdapter(Context context, List<String> mDatas){

        inflater = LayoutInflater.from(context);
        this.mDatas = mDatas;

        mHeights = new ArrayList<>();

        // 随机产生每个 item 的高度
        for (int i = 0; i < mDatas.size(); i++){
            mHeights.add((int)(100 + Math.random() * 300));
        }
    }
    // 创建 ViewHolder
    @Override
    public CrazyViewHolder onCreateViewHolder(ViewGroup viewGroup, int i) {
        View v = inflater.inflate(R.layout.staggered_item, viewGroup, false);

        return new CrazyViewHolder(v);
    }
    // 把数目绑定到条目上
    @Override
    public void onBindViewHolder(CrazyViewHolder crazyViewHolder, int i) {
        // 动态的去改变每一个 item 对应的 TextView 的高度
        ViewGroup.LayoutParams lp = crazyViewHolder.tvNum.getLayoutParams();
        lp.height = mHeights.get(i);
        crazyViewHolder.tvNum.setLayoutParams(lp);

        String num = mDatas.get(i);
        crazyViewHolder.tvNum.setText(num);
    }

    @Override
    public int getItemCount() {
        return mDatas.size();
    }

    public class CrazyViewHolder extends RecyclerView.ViewHolder{

        TextView tvNum;

        public CrazyViewHolder(View itemView) {
            super(itemView);
            tvNum = (TextView)itemView.findViewById(R.id.tv_stagger);
        }
    }
}

drawable 文件下的 divider_bg.xml :

<?xml version="1.0" encoding="utf-8"?>
<shape xmlns:android="http://schemas.android.com/apk/res/android"
    android:shape="rectangle">

    <gradient
        android:startColor="#ffff0000"
        android:centerColor="#ff00ff00"
        android:endColor="#ff0000ff"
        android:type="linear"/>
    <size android:height="4dp" android:width="4dp"/>

</shape>

在 styles.xml 中定义主题：

<?xml version="1.0" encoding="utf-8"?>
<resources>
    <style name="AppTheme" parent="android:Theme.Material.Light">
        <item name="android:listDivider">@drawable/divider_bg</item>
    </style>
</resources>