PickerView可以滑动选择的pickerView工具类（转载）

package com.service.ybs.view;

import java.util.ArrayList;
import java.util.List;
import java.util.Timer;
import java.util.TimerTask;

import android.content.Context;
import android.graphics.Canvas;
import android.graphics.Paint;
import android.graphics.Paint.Align;
import android.graphics.Paint.FontMetricsInt;
import android.graphics.Paint.Style;
import android.os.Handler;
import android.os.Message;
import android.util.AttributeSet;
import android.view.MotionEvent;
import android.view.View;

public class PickerView extends View{
    public static final String TAG = "PickerView";
    /**
     * text之间间距和minTextSize之比
     */
    public static final float MARGIN_ALPHA = 2.8f;
    /**
     * 自动回滚到中间的速度
     */
    public static final float SPEED = 2;
 
    private List<String> mDataList;
    /**
     * 选中的位置，这个位置是mDataList的中心位置，一直不变
     */
    private int mCurrentSelected;
    private Paint mPaint;
 //min 40 max 80
    private float mMaxTextSize = 55;
    private float mMinTextSize = 40;
 
    private float mMaxTextAlpha = 255;
    private float mMinTextAlpha = 120;
 
    private int mColorText = 0x333333;
 
    private int mViewHeight;
    private int mViewWidth;
 
    private float mLastDownY;
    /**
     * 滑动的距离
     */
    private float mMoveLen = 0;
    private boolean isInit = false;
    private onSelectListener mSelectListener;
    private Timer timer;
    private MyTimerTask mTask;
 
    Handler updateHandler = new Handler()
    {
 
        @Override
        public void handleMessage(Message msg)
        {
            if (Math.abs(mMoveLen) < SPEED)
            {
                mMoveLen = 0;
                if (mTask != null)
                {
                    mTask.cancel();
                    mTask = null;
                    performSelect();
                }
            } else
                // 这里mMoveLen / Math.abs(mMoveLen)是为了保有mMoveLen的正负号，以实现上滚或下滚
                mMoveLen = mMoveLen - mMoveLen / Math.abs(mMoveLen) * SPEED;
            invalidate();
        }
 
    };
 
    public PickerView(Context context)
    {
        super(context);
        init();
    }
 
    public PickerView(Context context, AttributeSet attrs)
    {
        super(context, attrs);
        init();
    }
 
    public void setOnSelectListener(onSelectListener listener)
    {
        mSelectListener = listener;
    }
 
    private void performSelect()
    {
        if (mSelectListener != null)
            mSelectListener.onSelect(mDataList.get(mCurrentSelected));
    }
 
    public void setData(List<String> datas)
    {
        mDataList = datas;
        mCurrentSelected = datas.size() / 2;
        invalidate();
    }
 
    public void setSelected(int selected)
    {
        mCurrentSelected = selected;
    }
 
    private void moveHeadToTail()
    {
        String head = mDataList.get(0);
        mDataList.remove(0);
        mDataList.add(head);
    }
 
    private void moveTailToHead()
    {
        String tail = mDataList.get(mDataList.size() - 1);
        mDataList.remove(mDataList.size() - 1);
        mDataList.add(0, tail);
    }
 
    @Override
    protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec)
    {
        super.onMeasure(widthMeasureSpec, heightMeasureSpec);
        mViewHeight = getMeasuredHeight();
        mViewWidth = getMeasuredWidth();
        // 按照View的高度计算字体大小
        //4.0f
        mMaxTextSize = mViewHeight / 8.0f;
        mMinTextSize = mMaxTextSize /2f;
        isInit = true;
        invalidate();
    }
 
    private void init()
    {
        timer = new Timer();
        mDataList = new ArrayList<String>();
        mPaint = new Paint(Paint.ANTI_ALIAS_FLAG);
        mPaint.setStyle(Style.FILL);
        mPaint.setTextAlign(Align.CENTER);
        mPaint.setColor(mColorText);
    }
 
    @Override
    protected void onDraw(Canvas canvas)
    {
        super.onDraw(canvas);
        // 根据index绘制view
        if (isInit)
            drawData(canvas);
    }
 
    private void drawData(Canvas canvas)
    {
        // 先绘制选中的text再往上往下绘制其余的text 4.0
        float scale = parabola(mViewHeight / 5.0f, mMoveLen);
        float size = (mMaxTextSize - mMinTextSize) * scale + mMinTextSize;
        mPaint.setTextSize(size);
        mPaint.setAlpha((int) ((mMaxTextAlpha - mMinTextAlpha) * scale + mMinTextAlpha));
        // text居中绘制，注意baseline的计算才能达到居中，y值是text中心坐标
        float x = (float) (mViewWidth / 2.0);
        float y = (float) (mViewHeight / 2.0 + mMoveLen);
        FontMetricsInt fmi = mPaint.getFontMetricsInt();
        float baseline = (float) (y - (fmi.bottom / 2.0 + fmi.top / 2.0));
 
        canvas.drawText(mDataList.get(mCurrentSelected), x, baseline, mPaint);
        // 绘制上方data
        for (int i = 1; (mCurrentSelected - i) >= 0; i++)
        {
            drawOtherText(canvas, i, -1);
        }
        // 绘制下方data
        for (int i = 1; (mCurrentSelected + i) < mDataList.size(); i++)
        {
            drawOtherText(canvas, i, 1);
        }
 
    }
 
    /**
     * @param canvas
     * @param position
     *            距离mCurrentSelected的差值
     * @param type
     *            1表示向下绘制，-1表示向上绘制
     */
    private void drawOtherText(Canvas canvas, int position, int type)
    {
        float d = (float) (MARGIN_ALPHA * mMinTextSize * position + type
                * mMoveLen);
        //4.0
        float scale = parabola(mViewHeight / 5.0f, d);
        float size = (mMaxTextSize - mMinTextSize) * scale + mMinTextSize;
        mPaint.setTextSize(size);
        mPaint.setAlpha((int) ((mMaxTextAlpha - mMinTextAlpha) * scale + mMinTextAlpha));
        float y = (float) (mViewHeight / 2.0 + type * d);
        FontMetricsInt fmi = mPaint.getFontMetricsInt();
        float baseline = (float) (y - (fmi.bottom / 2.0 + fmi.top / 2.0));
        canvas.drawText(mDataList.get(mCurrentSelected + type * position),
                (float) (mViewWidth / 2.0), baseline, mPaint);
    }
 
    /**
     * 抛物线
     *
     * @param zero
     *            零点坐标
     * @param x
     *            偏移量
     * @return scale
     */
    private float parabola(float zero, float x)
    {
        float f = (float) (1 - Math.pow(x / zero, 2));
        return f < 0 ? 0 : f;
    }
 
    @Override
    public boolean onTouchEvent(MotionEvent event)
    {
        switch (event.getActionMasked())
        {
        case MotionEvent.ACTION_DOWN:
            doDown(event);
            break;
        case MotionEvent.ACTION_MOVE:
            doMove(event);
            break;
        case MotionEvent.ACTION_UP:
            doUp(event);
            break;
        }
        return true;
    }
 
    private void doDown(MotionEvent event)
    {
        if (mTask != null)
        {
            mTask.cancel();
            mTask = null;
        }
        mLastDownY = event.getY();
    }
 
    private void doMove(MotionEvent event)
    {
 
        mMoveLen += (event.getY() - mLastDownY);
 
        if (mMoveLen > MARGIN_ALPHA * mMinTextSize / 2)
        {
            // 往下滑超过离开距离
            moveTailToHead();
            mMoveLen = mMoveLen - MARGIN_ALPHA * mMinTextSize;
        } else if (mMoveLen < -MARGIN_ALPHA * mMinTextSize / 2)
        {
            // 往上滑超过离开距离
            moveHeadToTail();
            mMoveLen = mMoveLen + MARGIN_ALPHA * mMinTextSize;
        }
 
        mLastDownY = event.getY();
        invalidate();
    }
 
    private void doUp(MotionEvent event)
    {
        // 抬起手后mCurrentSelected的位置由当前位置move到中间选中位置
        if (Math.abs(mMoveLen) < 0.0001)
        {
            mMoveLen = 0;
            return;
        }
        if (mTask != null)
        {
            mTask.cancel();
            mTask = null;
        }
        mTask = new MyTimerTask(updateHandler);
        timer.schedule(mTask, 0, 10);
    }
 
    class MyTimerTask extends TimerTask
    {
        Handler handler;
 
        public MyTimerTask(Handler handler)
        {
            this.handler = handler;
        }
 
        @Override
        public void run()
        {
            handler.sendMessage(handler.obtainMessage());
        }
 
    }
 
    public interface onSelectListener
    {
        void onSelect(String text);
    }
}

//xml中的使用

<com.service.ybs.view.PickerView
                android:id="@+id/second_pv"
                android:layout_width="wrap_content"
                android:layout_height="160dp" />

//activity中的使用

second_pv = (PickerView) findViewById(R.id.second_pv);

lists_city = new ArrayList<String>();

lists.add("粤");
        lists.add("豫");
        lists.add("川");
        lists.add("京");
        lists.add("津");
        lists.add("冀 ");
        lists.add("晋");
        lists.add("辽");
        lists.add("吉");

second_pv.setData(lists_city);
                second_pv.setOnSelectListener(new onSelectListener() {

                    @Override
                    public void onSelect(String text) {
                        cityTv.setText(text);
                    }
                });
            }
        });