Android PickerView的实现

话不多说，直接上图

这样子的PickerView，也就是自定义一个View。直接上代码

/*
 * 使用：xml文件中直接引用，需要多少列数据就用多少个PickerView
 * 在Activity中：获取到PickerView实例后，使用setData()方法设置数据，其他方法见103行
 * 关联数据:比如现在第一列选中xx市,可以在监听中为第二个PickerView调用setData()来更新第二列的数据
 */
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;
    /**
     * 默认初始化时选中的位置，这个位置是mDataList的中心位置，一直不变
     */
    private int mCurrentSelected;
    private Paint mPaint;

    private float mMaxTextSize = 80;
    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();
        }

    };

    //构造方法都调用init
    public PickerView(Context context)
    {
        super(context);
        init();
    }

    public PickerView(Context context, AttributeSet attrs)
    {
        super(context, attrs);
        init();
    }
    //以下为主要使用的public方法---------------------------------------------------------------------------------

    /*
     * 获取到当前选中的数据在数据集中的position
     */
    public int getCurrentItem(){
        return mCurrentSelected;
    };
    /*
     * 设置监听,这个onSelectedLisener需要实现一个onSelect(String text)方法
     * text是当前显示的数据
     */
    public void setOnSelectListener(onSelectListener listener)
    {
        mSelectListener = listener;
    }
    /*
     * 设置数据集，参数类型为List
     */
    public void setData(List<String> datas)
    {
        mDataList = datas;
        mCurrentSelected = datas.size() / 2;
        invalidate();
    }
    /*
     * 设置当前选中的数据
     */
    public void setSelected(int selected)
    {
        mCurrentSelected = selected;
    }

    //-------------------------------------------------------------------------------------
    private void performSelect()
    {
        if (mSelectListener != null)
            mSelectListener.onSelect(mDataList.get(mCurrentSelected));
    }



    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
        mMaxTextSize = mViewHeight / 4.0f;
        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(Paint.Style.FILL);
        mPaint.setTextAlign(Paint.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
        float scale = parabola(mViewHeight / 4.0f, 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);
        Paint.FontMetricsInt fmi = mPaint.getFontMetricsInt();
        float baseline = (float) (y - (fmi.bottom / 2.0 + fmi.top / 2.0));

        canvas.drawText(mDataList.get(mCurrentSelected), x, baseline, mPaint);
        Paint linePaint=new Paint();
        linePaint.setColor(Color.LTGRAY);
        linePaint.setStrokeWidth(3);



        // 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);
        float scale = parabola(mViewHeight / 4.0f, 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);
        Paint.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);
    }

在xml中引用

<?xml version="1.0" encoding="utf-8"?>
<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">
    <LinearLayout
        android:layout_centerHorizontal="true"
        android:orientation="horizontal"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content">
        <com.liu.pickerview.PickerView
            android:id="@+id/year_picker"
            android:layout_width="100dp"
            android:layout_height="100dp" />
        <com.liu.pickerview.PickerView
            android:id="@+id/month_picker"
            android:layout_width="100dp"
            android:layout_height="100dp" />
    </LinearLayout>

</RelativeLayout>

在java代码中调用

public class MainActivity extends AppCompatActivity {
    private PickerView year, month;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        year = (PickerView) findViewById(R.id.year_picker);
        month = (PickerView) findViewById(R.id.month_picker);

        ArrayList<String> month_list=new ArrayList<>();
        for (int i=0;i<12;i++){
            month_list.add(i + "");
        }
        ArrayList<String> year_list=new ArrayList<>();
        for (int i=0;i<100;i++){
            year_list.add( i + "");
        }

        year.setData(year_list);
        month.setData(month_list);


        year.setOnSelectListener(new PickerView.onSelectListener() {
            @Override
            public void onSelect(String text) {
                Log.i("tag","选择了"+text);
            }
        });
        month.setOnSelectListener(new PickerView.onSelectListener() {
            @Override
            public void onSelect(String text) {
                Log.i("tag","选择了"+text);
            }
        });
    }
}

demo下载地址:http://download.youkuaiyun.com/detail/u013290075/9304729