RecyclerView实现滚动轮

实现原理使用LinearSnalphelper实现元素居中（如果对SnapHelper不了解的话建议百度下），使用ViewType实现偏移。

具体效果：

实现：

package com.david.mytest.test.wheeltest;

import android.content.Context;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Paint;
import android.support.annotation.Nullable;
import android.support.v7.widget.LinearLayoutManager;
import android.support.v7.widget.LinearSnapHelper;
import android.support.v7.widget.RecyclerView;
import android.util.AttributeSet;
import android.util.TypedValue;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.TextView;

import com.david.mytest.R;
import com.david.mytest.ui.pulltorefresh.pulltorefreshorigin.progress.Utils;

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

/**

• Created by wb-cuiweixing on 2016/7/5.
  */
  public class RecyclerWheelView extends RecyclerView {
  public interface OnSelectListener{
  void onSelect(int position);
  }

  private ArrayList mData;
  private int mOffset = 2;//默认每页显示五条
  private float mItemHeight;
  private int mWidth;
  private LinearLayoutManager mManager;
  private LinearSnapHelper mSnapHelper;

  private OnSelectListener mOnSelectListener;

  public RecyclerWheelView(Context context) {
  super(context);
  initData();
  }

  public RecyclerWheelView(Context context, @Nullable AttributeSet attrs) {
  super(context, attrs);
  initData();
  }

  public RecyclerWheelView(Context context, @Nullable AttributeSet attrs, int defStyle) {
  super(context, attrs, defStyle);
  initData();
  }

  private void initData() {
  mData = new ArrayList<>();

   mItemHeight = TypedValue.applyDimension(TypedValue.COMPLEX_UNIT_DIP, 45, getResources().getDisplayMetrics());
   mManager = new LinearLayoutManager(getContext());
   mManager.setOrientation(LinearLayoutManager.VERTICAL);
  
   if (null == paint) {
       paint = new Paint();
       paint.setColor(Color.parseColor("#83cde6"));
       paint.setStrokeWidth(2f);
   }
   post(new Runnable() {
       @Override
       public void run() {//RecyclerView还未初始化完成不能直接调用其方法否则会报空指针，类构造方法中只能进行初始化成员变量
           getLayoutParams().height = (int) (mItemHeight * (mOffset * 2 + 1));
           setLayoutManager(mManager);
  
           setAdapter(new MySpaceAdapter());
  
           getAdapter().notifyDataSetChanged();
  
           mWidth = getWidth();
       }
   });
  
   mSnapHelper = new LinearSnapHelper();
   mSnapHelper.attachToRecyclerView(this);
  

  }

  public ArrayList getData() {
  if (mData.size() < 1) {
  return null;
  }
  ArrayList data = new ArrayList<>();
  for (int i = 1; i < mData.size() - 1; i++) {
  data.add(mData.get(i));
  }
  return data;
  }

  public void setData(ArrayList data) {
  this.mData.clear();
  this.mData.addAll(data);
  mData.add(0, null);
  mData.add(null);
  if (getAdapter() != null)
  getAdapter().notifyDataSetChanged();
  }

  private List textViews;

  /**

  • RecyclerView实现WheelView
    */
    class MySpaceAdapter extends RecyclerView.Adapter {

    MySpaceAdapter() {
    textViews = new ArrayList<>();
    }

    @Override
    public RecyclerView.ViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
    if (viewType == 1) {
    return new SpaceViewHolder(new View(getContext()));
    } else {
    View view = LayoutInflater.from(getContext()).inflate(R.layout.item_recycler_wheel, parent, false);
    textViews.add((TextView) view);
    return new NormalViewHolder(view);
    }
    }

    @Override
    public void onBindViewHolder(RecyclerView.ViewHolder holder, int position) {
    if (holder instanceof NormalViewHolder) {
    TextView textView = ((NormalViewHolder) holder).mText;
    textView.setText(mData.get(position));
    }
    }

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

    @Override
    public int getItemViewType(int position) {
    return (position == 0 || position == mData.size() - 1) ? 1 : 0;
    }
    }

  class NormalViewHolder extends RecyclerView.ViewHolder {
  TextView mText;

   NormalViewHolder(View itemView) {
       super(itemView);
       mText = (TextView) itemView;
       mText.getLayoutParams().height = (int) mItemHeight;
   }
  

  }

  class SpaceViewHolder extends RecyclerView.ViewHolder {
  SpaceViewHolder(View itemView) {
  super(itemView);
  //根据每一条高度及偏移量设置高度
  float height = mOffset * mItemHeight;
  itemView.setLayoutParams(new ViewGroup.LayoutParams(ViewGroup.LayoutParams.MATCH_PARENT, (int) height));
  }
  }

  @Override
  protected void onScrollChanged(int l, int t, int oldl, int oldt) {
  super.onScrollChanged(l, t, oldl, oldt);
  /**
  * 手动滑动或者惯性滑动时触发该方法，不过由于本身没有滑动所以l,t,oldl,oldt都是0
  * 此处只是在滑动时设置相应状态
  */
  View viewContainer = mSnapHelper.findSnapView(mManager);//获取中间位置的view
  TextView textView = ((NormalViewHolder) getChildViewHolder(viewContainer)).mText;

   int centerPosition = mData.indexOf(textView.getText().toString());
   if (mCenterPosition == centerPosition) {
       return;
   }
   mCenterPosition = centerPosition;
  
   for (TextView view : textViews) {//设置选中颜色
       view.setTextColor(Color.parseColor("#dddddd"));
       if (view == textView) {
           view.setTextColor(Color.parseColor("#0288ce"));
       }
   }
  
   if (mOnSelectListener != null) {
       //第一条是占位条
       mOnSelectListener.onSelect(mCenterPosition - 1);
   }
  

  }

  private int mCenterPosition;//获取选中位置时要减一（有占位条）
  private Paint paint;

  /**

  • 获取选中区域的边界
    */
    private int[] selectedAreaBorder;

  private int[] obtainSelectedAreaBorder() {
  if (null == selectedAreaBorder) {
  selectedAreaBorder = new int[2];
  selectedAreaBorder[0] = (int) (mItemHeight * mOffset);
  selectedAreaBorder[1] = (int) (mItemHeight * (mOffset + 1));
  }
  return selectedAreaBorder;
  }

  @Override
  public void onDraw(Canvas c) {
  super.onDraw©;
  c.drawLine(mWidth * 1.0F / 6, obtainSelectedAreaBorder()[0], mWidth * 5 / 6, obtainSelectedAreaBorder()[0], paint);
  c.drawLine(mWidth * 1.0F / 6, obtainSelectedAreaBorder()[1], mWidth * 5 / 6, obtainSelectedAreaBorder()[1], paint);
  }

  public void setmOnSelectListener(OnSelectListener mOnSelectListener) {
  this.mOnSelectListener = mOnSelectListener;
  }
  }

一般是用点击确定后获取选中位置，OnSelectListener是在滑动选中时执行的。