最近做项目，遇到一个需要实现滚动选择的需求。以前做过一个自定义实现滚动选择的view(/u014763302/article/details/53104814)，但发现不大符合需求。本着快速实现的目标，就找到了这为大神的博客（/zhongkejingwang/article/details/38513301），看了下实现的差不多了，就拿过来用，顺便加了一些小功能，并对存在的bug做了一些优化，特记录。
目前需求：
上下可循环滚动选择点击按钮自动上下滚动一格效果如下：
思路讲解：
由于代码本身是基于上面博文的基础上来的，逻辑大部分还是没变，需要细节的请移步开头的链接，博文中思路细节大神讲的很明白。
说下我添加的功能及优化的地方：
点击按钮自动滚动一格：原来的滚动实现是基于触摸事件+记录滑动距离，因此自动滚动也基于一样的逻辑：主动调用触摸方法模拟触摸事件。原博文存在瞬滑时回滚很多造成不友好现象，修复是在ACTION_UP时通过计算矫正滑动位置和data item的对应关系。
下面上代码。
package com.example.wheelview;import android.animation.Animator;import android.animation.AnimatorListenerAdapter;import android.animation.ValueAnimator;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;import android.view.animation.LinearInterpolator;import java.util.ArrayList;import java.util.List;/*** 滚动选择器,/zhongkejingwang/article/details/38513301** @author huanghp*/public class PickerView extends View {public static final String TAG = "PickerView";//minTextSize和text之间间距之比public static final float MARGIN_ALPHA = 1.56f;//自动回滚到中间的速度public static final byte SPEED = 2;public static final byte PERIOD = 10;public static final byte CODE = 0X10;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;private float mMaxTextSize = 48;private float mMinTextSize = 32;private float mMaxTextAlpha = 255;private float mMinTextAlpha = 120;private int mColorText = 0xffffff;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 volatile boolean isInAnimate;private Handler updateHandler = new Handler() {@Overridepublic void handleMessage(Message msg) {if (Math.abs(mMoveLen) < SPEED) {mMoveLen = 0;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;sendEmptyMessageDelayed(CODE, PERIOD);}invalidate();}};public PickerView(Context context) {this(context, null);}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) {if (datas != null) {mDataList.addAll(datas);}mCurrentSelected = mDataList.size() / 2;performSelect();invalidate();}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);}@Overrideprotected 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() {mDataList = new ArrayList<>();mPaint = new Paint(Paint.ANTI_ALIAS_FLAG);mPaint.setStyle(Style.FILL);mPaint.setTextAlign(Align.CENTER);mPaint.setColor(mColorText);// mPaint.setTypeface(Typeface.create("eurostile", Typeface.NORMAL));}@Overrideprotected void onDraw(Canvas canvas) {super.onDraw(canvas);if (isInit) drawData(canvas);}private void drawData(Canvas canvas) {if (mDataList.isEmpty()) return;// 先绘制选中的text再往上往下绘制其余的textfloat 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);FontMetricsInt fmi = mPaint.getFontMetricsInt();float baseline = (float) (y - (fmi.bottom / 2.0 + fmi.top / 2.0));//这里是经过简化后的公式canvas.drawText(mDataList.get(mCurrentSelected), x, baseline, mPaint);// 绘制上方datafor (int i = 1; (mCurrentSelected - i) >= 0; i++) {drawOtherText(canvas, i, -1);}// 绘制下方datafor (int i = 1; (mCurrentSelected + i) < mDataList.size(); i++) {drawOtherText(canvas, i, 1);}}/*** @param canvas* @param position 距离mCurrentSelected的差值* @param type1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);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;}@Overridepublic 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) {updateHandler.removeMessages(CODE);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;}//这段是为了修正瞬滑导致回滚较多现象，屏蔽亦可if (Math.abs(mMoveLen) > MARGIN_ALPHA * mMinTextSize / 2) {int m = (int) (Math.abs(mMoveLen) / (MARGIN_ALPHA * mMinTextSize / 2));for (int i = 0; i < m; i++) {if (mMoveLen > 0) moveTailToHead();else moveHeadToTail();}if (mMoveLen > 0) mMoveLen -= MARGIN_ALPHA * mMinTextSize * m / 2;else mMoveLen += MARGIN_ALPHA * mMinTextSize * m / 2;}updateHandler.removeMessages(CODE);updateHandler.sendEmptyMessage(CODE);}/*** @param up 是否向上滑动*/public void autoScroll(boolean up) {if (isInAnimate) return;isInAnimate = true;final float[] values = up ? new float[]{MARGIN_ALPHA * mMinTextSize + 1, 0} : new float[]{0, MARGIN_ALPHA * mMinTextSize + 1};ValueAnimator va = ValueAnimator.ofFloat(values);va.setDuration(100);va.setInterpolator(new LinearInterpolator());va.addUpdateListener(new ValueAnimator.AnimatorUpdateListener() {@Overridepublic void onAnimationUpdate(ValueAnimator animation) {float v = (float) animation.getAnimatedValue();doMove(MotionEvent.obtain(System.currentTimeMillis(), 0, 0, 0f, v, 0));}});va.addListener(new AnimatorListenerAdapter() {@Overridepublic void onAnimationEnd(Animator animation) {doUp(null);isInAnimate = false;}@Overridepublic void onAnimationStart(Animator animation) {doDown(MotionEvent.obtain(System.currentTimeMillis(), 0, 0, 0f, values[0], 0));}});va.start();}public interface onSelectListener {void onSelect(String text);}}
谢谢！
