RecycleView的基本使用(一)

简介

RecycleView是Android5.0引入的控件，不过我们低版本也是可以使用的，只需引入android_support_v7包即可。RecycleView相比ListView,GridView，更加灵活，它只做回收和复用工作，而其他的就需要我们开发者自己去实现。通过设置它提供的不同LayoutManager，ItemDecoration , ItemAnimator就可实现我们想要的效果：

• LayoutManager：控制我们的显示方式
• ItemDecoration ：设置分割线和分割间隔
• ItemAnimator：条目增加，删除的动画
• OnClickListener：需要自己去实现。

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基本使用

我们先按照ListView的方式写一下代码

Activity

    public class MainActivity extends AppCompatActivity {

    private RecyclerView mRecyclerView;
    private ArrayList<String> mLists;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        initData();
        initView();
    }

    private void initView() {
        mRecyclerView = (RecyclerView)findViewById(R.id.main_rlist);
        mRecyclerView.setLayoutManager(new LinearLayoutManager(this));
        MainListAdapter adapter = new MainListAdapter(this, mLists);
        mRecyclerView.setAdapter(adapter);
    }
    private void initData() {
        mLists = new ArrayList<String>();
        for (int i =0;i<20;i++){
            mLists.add("recyclerViewitem::"+i);
        }
    }

}

xml

<?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/main_rlist"
        android:layout_width="match_parent"
        android:layout_height="match_parent"/>
</RelativeLayout>

Adapter

在使用RecycleView，Adapter必须是RecycleView自带的Adapter:

public class MainListAdapter extends RecyclerView.Adapter<MainListAdapter.MyViewHolder>{

    private ArrayList<String> mList;
    private Context mContext;

    public MainListAdapter(Context context,ArrayList<String> lists){
        mList = lists;
        mContext = context;
    }

    @Override
    public int getItemCount() {
        return mList!=null?mList.size():0;
    }

    @Override
    public MyViewHolder onCreateViewHolder(ViewGroup  parent, int viewType) {
        MyViewHolder holder = new MyViewHolder(LayoutInflater.from(mContext).inflate(R.layout.layout_item,parent,false));
        return holder;
    }

    @Override
    public void onBindViewHolder(MyViewHolder holder, int position) {
        holder.tv.setText(mList.get(position));
    }

    static class MyViewHolder extends RecyclerView.ViewHolder{
        TextView tv;
        public MyViewHolder(View view)
        {
            super(view);
            tv = (TextView) view.findViewById(R.id.item_tv);
        }
    }
}

从上面代码我们可以看到，RecycleView已经默认实现ViewHodler了，那么我们只需要按照它的格式书写即可。

下面我们来看下效果：

这样是没有分割线的，需要ItemDecoration，而ItemDecoration是一个抽象类，需要我们自己去实现相应的方法:

 - 顺序：onDraw()--drawChild--onDrawOver()
 - getItemOffsets :可以通过outRect.set()为每个Item设置一定的偏移量，主要用于绘制Decorator

RecyclerItemDecoration

public class RecyclerItemDecoration extends RecyclerView.ItemDecoration {
    private Paint mPaint;
    public RecyclerItemDecoration() {
        super();
    }

    @Override
    public void onDraw(Canvas c, RecyclerView parent, RecyclerView.State state) {
        final int left = parent.getPaddingLeft();
        final int right = parent.getWidth() - parent.getPaddingRight();
        final int childCount = parent.getChildCount();
        if(mPaint==null){
            mPaint = new Paint();
            mPaint.setColor(Color.BLUE);
        }
        if(childCount>0){
            for (int i = 0; i < childCount; i++) {
                View v = parent.getChildAt(i);
                c.drawLine(left,v.getBottom(),right,v.getBottom(),mPaint);
            }
        }

    }

    @Override
    public void onDrawOver(Canvas c, RecyclerView parent, RecyclerView.State state) {
        super.onDrawOver(c, parent, state);
    }

    @Override
    public void getItemOffsets(Rect outRect, View view, RecyclerView parent, RecyclerView.State state) {
          outRect.set(0, 0, 0, 0);
    }

这里，只是在简单画了一条线，看看效果：

这样写RecyclerItemDecoration ，拓展性太差，我们可以这样写：

RecyclerItemsDecoration

public class RecyclerItemsDecoration 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 RecyclerItemsDecoration(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);
            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);
        }
    }
}

使用的时候这样写：

mRecyclerView.addItemDecoration(new RecyclerItemsDecoration(this,RecyclerItemsDecoration.VERTICAL_LIST));

看看效果：

由于我们用的是系统的，这是默认效果，我们还可以在style里去修改样式，比如：
style.xml

<style name="AppTheme" parent="Theme.AppCompat.Light.DarkActionBar">
        <item name="android:listDivider">@drawable/list_divider</item>
    </style>

list_divider，我们自定义一个shapeDrawable:

list_divider.xml

<?xml version="1.0" encoding="utf-8"?>
<shape xmlns:android="http://schemas.android.com/apk/res/android"
    android:shape="rectangle">
    <gradient
        android:centerColor="#3366cc"
        android:endColor="#00cc00"
        android:startColor="#ffcc00"
        android:type="linear"
        />
    <size android:height="2dp"/>
</shape>

看看效果：

所以，我们可以根据项目需求更改分割线，是不是很赞。反正都是自己写，随便整~

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关于如何实现GridView和瀑布流效果，会在下篇文章中记录。