明日之星——RecyclerView(一)

　　在Listview中使用了很久的viewholder、setTag、getTag来实现Item复用后， Google大大终于看不下去了。推出了明日之星RecyclerView，现已加入support.v7豪华套餐。顾名思义，RecyclerView本身是不管怎么布局的。它本身只负责，加载看得见的viewHolder，释放看不见的viewHolder。这一功能就代替掉了，ListView中麻烦的Item复用设计。而对于布局的控制，RecyclerView则依赖于LayoutManager。下面，我用一个简单的demo，记录下RecyclerView的用法。

一、如何加入support.v7包(Android Studio中)。

方法1:右键项目->Open Module Settings->Dependencies->绿色加号->Library dependency -> recyclerview-v7->OK

方法2:

dependencies {
    compile fileTree(include: ['*.jar'], dir: 'libs')
    compile 'com.android.support:appcompat-v7:22.1.1'
    compile 'com.android.support:recyclerview-v7:22.1.1'
}

in build.gradle

二、我自定义了MyRecyclerView继承RecyclerView，这不是必需的，我只是为了方便以后扩展。

三、完成布局文件中　　activity_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">

    <fallflowscrollviewdemo.com.dream.fishbonelsy.recyclerdemo.MyRecyclerView
        android:id="@+id/recycler_view_id"
        android:layout_width="match_parent"
        android:layout_height="match_parent">

    </fallflowscrollviewdemo.com.dream.fishbonelsy.recyclerdemo.MyRecyclerView>

</RelativeLayout>

四、完成Item的布局　　normal_item_layout.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:orientation="vertical">

    <TextView
        android:id="@+id/normal_item_id"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_marginLeft="3dp"
        android:layout_marginRight="3dp"
        android:layout_marginTop="5dp"
        android:background="#44ff0000"
        android:gravity="center"
        android:textSize="30sp" />

</LinearLayout>

五、完成Item的ViewHolder，并给予子控件实例。　　MyRecyclerViewHold.java

import android.support.v7.widget.RecyclerView;
import android.view.View;
import android.widget.TextView;

/**
 * Created by fishboneLsy on 2015/7/2.
 */
public class MyRecyclerViewHold<E extends Object> extends RecyclerView.ViewHolder {

    private TextView textView;

    public MyRecyclerViewHold(View itemView) {
        super(itemView);
        textView = (TextView) itemView.findViewById(R.id.normal_item_id);
    }

    public void setItemContent(E data){
        textView.setText(data.toString());
    }
}

六、实现RecyclerView的适配器RecyclerViewAdapter。　　MyRecyclerViewAdapter.java

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

import java.util.List;

/**
 * Created by fishboneLsy on 2015/7/2.
 */
public class MyRecyclerViewAdapter extends RecyclerView.Adapter<MyRecyclerViewHold> {

    private Context mContext;
    private List<?> mDataList;
    private int mNormalItemLayout;

　　 /**

　　 * MyRecyclerViewAdapter Construct
 　　* @param context
 　　* @param dataList  
 　　* @param layoutId  ItemLayoutId
 　　*/

    public MyRecyclerViewAdapter(Context context, List<?> dataList, int layoutId) {
        mContext = context;
        mDataList = dataList;
        mNormalItemLayout = layoutId;
    }

    @Override
    public int getItemViewType(int position) {
        return super.getItemViewType(position);
    }

    @Override
    public MyRecyclerViewHold onCreateViewHolder(ViewGroup parent, int viewType) {
      
        View view = LayoutInflater.from(mContext).inflate(mNormalItemLayout, parent, false);
        MyRecyclerViewHold viewHold = new MyRecyclerViewHold(view);
        return viewHold;                
    }

    @Override
    public void onBindViewHolder(MyRecyclerViewHold holder, int position) {
        try {
            holder.setItemContent(mDataList.get(position));
        }catch (Exception e){
            e.printStackTrace();
        }
    }

    @Override
    public int getItemCount() {
        if (mDataList != null && mDataList.size() > 0) {
            return mDataList.size();
        }
        return 0;
    }
}

adapter中包含了四个方法，它们分别是：

1、public int getItemViewType(int position) 获取Item的类型，默认是0。

2、public MyRecyclerViewHold onCreateViewHolder(ViewGroup parent, int viewType) 生成Item的ViewHolder

3、public void onBindViewHolder(MyRecyclerViewHold holder, int position)将Item的ViewHolder与数据List连接

4、public int getItemCount()获取Item总数

七、在Activity中创建RecyclerView并配置参数、输入数据。

import android.app.Activity;
import android.support.v7.app.ActionBarActivity;
import android.os.Bundle;
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 MainActivity extends Activity {


    private MyRecyclerView recyclerView;
    private MyRecyclerViewAdapter adapter;
    private List<String> mDataList;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        recyclerView = (MyRecyclerView) findViewById(R.id.recycler_view_id);
        /* create LayoutManager */
        RecyclerView.LayoutManager layoutManager = new LinearLayoutManager(this);
        recyclerView.setLayoutManager(layoutManager);
        mDataList = new ArrayList<String>();
        adapter = new MyRecyclerViewAdapter(this , mDataList , R.layout.normal_item_layout);
        recyclerView.setAdapter(adapter);

        // create data for test
        for (int i = 0 ; i < 40 ; i++){
            StringBuilder stringBuilder = new StringBuilder();
            stringBuilder.append("test:").append(i);
            for (int j = 0 ; j < (int)(Math.random()*10) ; j++){
                stringBuilder.append("
"+j);
            }
            mDataList.add(stringBuilder.toString());
        }
        adapter.notifyDataSetChanged();
    }
}

其中，LayoutManager决定了RecyclerView的布局方式。可以通过更换LayoutManager来改变RecyclerView的布局方式。

按照上面的代码，呈现的效果如下：

我们可以将：

RecyclerView.LayoutManager layoutManager = new LinearLayoutManager(this);

改为：

RecyclerView.LayoutManager layoutManager = new StaggeredGridLayoutManager(4 , StaggeredGridLayoutManager.VERTICAL);

就可以轻松地完成4列瀑布流效果：

至此，RecyclerView的简单使用算是完成。但是RecyclerView也有一些缺点。比如，它没有headerView。这在一些需要头部的地方会显得很不方便。所以我在一开始就用了自定义的MyRecyclerView来继承RecyclerView为后面的扩展留了空间。

Done!