Android仿iPhone的时间轮的工具Demo

相信大家一定都见过iPhone上面的时间滚动轮的效果，类似一样的滚动来选择数据，非常有意思，动画效果也很生动，相比较安卓自带的spinner，TimePicker等控件，用户体验要好很多，但是不知道怎么在android上面去实现这样的效果，后来在网上搜索到了这一效果需要自定义view来实现，下载一个相关的的demo，由于不知道原作者的出处，没有放相关的连接，下下来后自己讲里面详细的进行了注释，整理成一篇blog，记录一下学习的过程，下面先放上我自己改动之后的效果图片：

由于代码比较多，只贴上了自定义view的相关代码，想看实际效果的话请下载整个demo研究

package com.cogent.iPhonewheel.widget;

import java.util.LinkedList;
import java.util.List;

import android.content.Context;
import android.graphics.Canvas;
import android.graphics.Paint;
import android.graphics.Rect;
import android.graphics.drawable.Drawable;
import android.graphics.drawable.GradientDrawable;
import android.graphics.drawable.GradientDrawable.Orientation;
import android.os.Handler;
import android.os.Message;
import android.text.Layout;
import android.text.StaticLayout;
import android.text.TextPaint;
import android.util.AttributeSet;
import android.util.FloatMath;
import android.view.GestureDetector;
import android.view.MotionEvent;
import android.view.View;
import android.view.GestureDetector.SimpleOnGestureListener;
import android.view.animation.Interpolator;
import android.widget.Scroller;

import com.cogent.iPhonewheel.Interface.OnWheelChangedListener;
import com.cogent.iPhonewheel.Interface.OnWheelScrollListener;
import com.cogent.iPhonewheel.Interface.WheelAdapter;
import com.cogent.iPhonewheel.UI.R;

/**
 * 自定义的滚轮view
 * 
 * @author Administrator
 * 
 */
public class WheelView extends View {
	/** 滚动持续的时间 */
	private static final int SCROLLING_DURATION = 400;

	/** 最少滚动的位置 */
	private static final int MIN_DELTA_FOR_SCROLLING = 1;

	/** 当前值和标签的颜色 */
	private static final int VALUE_TEXT_COLOR = 0xF0FF6347;

	/** item文字的颜色 */
	private static final int ITEMS_TEXT_COLOR = 0xFF000000;

	/** 顶部和底部阴影的颜色 */
	private static final int[] SHADOWS_COLORS = new int[] { 0xFF111111,
			0x00AAAAAA, 0x00AAAAAA };

	/** 附加的item的高度 */
	private static final int ADDITIONAL_ITEM_HEIGHT = 15;

	/** 字体大小 */
	private static final int TEXT_SIZE = 30;

	/** 顶部和底部item的偏移值 */
	private static final int ITEM_OFFSET = TEXT_SIZE / 5;

	/** item布局的附加宽度 */
	private static final int ADDITIONAL_ITEMS_SPACE = 10;

	/** 标签偏移值 */
	private static final int LABEL_OFFSET = 8;

	/** 左右padding值 */
	private static final int PADDING = 10;

	/** 默认可见的item数目 */
	private static final int DEF_VISIABLE_ITEMS = 5;

	/** 初始化wheeladpater */
	private WheelAdapter adapter = null;

	/** 当前item位置 */
	private int currentItem = 0;

	/** item宽度 */
	private int itemsWidth = 0;

	/** 标签宽度 */
	private int labelWidth = 0;

	/** 可见item数目 */
	private int visibleItems = DEF_VISIABLE_ITEMS;

	/** item高度 */
	private int itemHeight = 0;

	/** item的字符串属性对象 */
	private TextPaint itemsPaint;

	/** value的字符串属性对象 */
	private TextPaint valuePaint;

	// Layouts
	private StaticLayout itemsLayout, labelLayout, valueLayout;

	private String label;
	private Drawable centerDrawable;

	/** 顶部渐变drawable对象 */
	private GradientDrawable topShadow;

	/** 顶部渐变drawable对象 */
	private GradientDrawable bottomShadow;

	/** 滚动动作是否执行 */
	private boolean isScrollingPerformed;

	/** 滚动偏移量 */
	private int scrollingOffset;

	/** 手势侦测对象 */
	private GestureDetector gestureDetector;

	private Scroller scroller;
	private int lastScrollY;

	/** 是否可循环 */
	private boolean isCyclic = false;

	/** 实例化OnWheelChangedListener */
	private List<OnWheelChangedListener> changingListeners = new LinkedList<OnWheelChangedListener>();

	/** 实例化OnWheelScrollListener */
	private List<OnWheelScrollListener> scrollingListeners = new LinkedList<OnWheelScrollListener>();

	/**
	 * 3个参数构造函数
	 */
	public WheelView(Context context, AttributeSet attrs, int defStyle) {
		super(context, attrs, defStyle);
		initData(context);
	}

	/**
	 * 2个参数构造函数
	 */
	public WheelView(Context context, AttributeSet attrs) {
		super(context, attrs);
		initData(context);
	}

	/**
	 * 1个参数构造函数
	 */
	public WheelView(Context context) {
		super(context);
		initData(context);
	}

	private void initData(Context context) {
		gestureDetector = new GestureDetector(context, gestureListener);
		gestureDetector.setIsLongpressEnabled(false);// 设置手势长按不起作用

		scroller = new Scroller(context);
	}

	/**
	 * 获取滚轮适配器
	 * 
	 * @return
	 */
	public WheelAdapter getAdapter() {
		return adapter;
	}

	/**
	 * 设置滚轮适配器
	 * 
	 * @param adapter
	 */
	public void setAdapter(WheelAdapter adapter) {
		this.adapter = adapter;
		invalidateLayouts();
		invalidate();// 是视图无效

	}

	/**
	 * 设置指定的滚轮动画变化率
	 * 
	 * @param interpolator
	 */
	public void setInterpolator(Interpolator interpolator) {
		scroller.forceFinished(true);
		scroller = new Scroller(getContext(), interpolator);
	}

	/**
	 * 得到可见item的数目
	 * 
	 * @return the count of visible items
	 */
	public int getVisibleItems() {
		return visibleItems;
	}

	/**
	 * 设置可见item的数目
	 * 
	 * @param count
	 *            the new count
	 */
	public void setVisibleItems(int count) {
		visibleItems = count;
		invalidate();
	}

	/**
	 * 得到标签
	 * 
	 * @return
	 */
	public String getLabel() {
		return label;
	}

	/**
	 * 设置标签
	 * 
	 * @param newLabel
	 */
	public void setLabel(String newLabel) {
		if (label == null || !label.equals(newLabel)) {
			label = newLabel;
			labelLayout = null;
			invalidate();
		}
	}

	/**
	 * 增加滚轮变化监听器
	 * 
	 * @param listener
	 */
	public void addChangingListener(OnWheelChangedListener listener) {
		changingListeners.add(listener);
	}

	/**
	 * 移除滚轮变化监听器
	 * 
	 * @param listener
	 */
	public void removeChangingListener(OnWheelChangedListener listener) {
		changingListeners.remove(listener);
	}

	/**
	 * 通知改变的监听器
	 * 
	 * @param oldValue
	 * @param newValue
	 */
	protected void notifyChangingListeners(int oldValue, int newValue) {
		for (OnWheelChangedListener listener : changingListeners) {
			listener.onChanged(this, oldValue, newValue);
		}
	}

	/**
	 * 增加滚轮监听器
	 * 
	 * @param listener
	 *            the listener
	 */
	public void addScrollingListener(OnWheelScrollListener listener) {
		scrollingListeners.add(listener);
	}

	/**
	 * 移除滚轮监听器
	 * 
	 * @param listener
	 *            the listener
	 */
	public void removeScrollingListener(OnWheelScrollListener listener) {
		scrollingListeners.remove(listener);
	}

	/**
	 * 通知监听器开始滚动
	 */
	protected void notifyScrollingListenersAboutStart() {
		for (OnWheelScrollListener listener : scrollingListeners) {
			listener.onScrollingStarted(this);
		}
	}

	/**
	 * 通知监听器结束滚动
	 */
	protected void notifyScrollingListenersAboutEnd() {
		for (OnWheelScrollListener listener : scrollingListeners) {
			listener.onScrollingFinished(this);
		}
	}

	/**
	 * 取得当前item
	 * 
	 * @return
	 */
	public int getCurrentItem() {
		return currentItem;
	}

	/**
	 * 设置当前item
	 * @param index
	 * @param animated
	 */
	public void setCurrentItem(int index, boolean animated) {
		if (adapter == null || adapter.getItemsCount() == 0) {
			return;
		}
		if (index < 0 || index >= adapter.getItemsCount()) {
			if (isCyclic) {
				while (index < 0) {
					index += adapter.getItemsCount();
				}
				index %= adapter.getItemsCount();
			} else {
				return;
			}
		}
		if (index != currentItem) {
			if (animated) {
				scroll(index - currentItem, SCROLLING_DURATION);
			} else {
				invalidateLayouts();

				int old = currentItem;
				currentItem = index;

				notifyChangingListeners(old, currentItem);
				invalidate();
			}
		}
	}

	/**
	 * 设置当前item w/o 动画. 当index有误是不做任何响应.
	 * 
	 * @param index
	 *            the item index
	 */
	public void setCurrentItem(int index) {
		setCurrentItem(index, false);
	}

	/**
	 * 测试滚轮是否可循环.
	 * 
	 * @return true if wheel is cyclic
	 */
	public boolean isCyclic() {
		return isCyclic;
	}

	/**
	 * 设置滚轮循环标志
	 * 
	 * @param isCyclic
	 *            the flag to set
	 */
	public void setCyclic(boolean isCyclic) {
		this.isCyclic = isCyclic;

		invalidate();
		invalidateLayouts();
	}

	/**
	 * 使布局无效
	 */
	private void invalidateLayouts() {
		itemsLayout = null;
		valueLayout = null;
		scrollingOffset = 0;
	}

	/**
	 * 初始化资源信息
	 */
	private void initResourceIfNecessary() {
		if (itemsPaint == null) {
			itemsPaint = new TextPaint(Paint.ANTI_ALIAS_FLAG
					| Paint.FAKE_BOLD_TEXT_FLAG);
			itemsPaint.setTextSize(TEXT_SIZE);
		}

		if (valuePaint == null) {
			valuePaint = new TextPaint(Paint.ANTI_ALIAS_FLAG
					| Paint.FAKE_BOLD_TEXT_FLAG | Paint.DITHER_FLAG);
			valuePaint.setTextSize(TEXT_SIZE);
			valuePaint.setShadowLayer(0.1f, 0, 0.1f, 0xFFC0C0C0);
		}

		if (centerDrawable == null) {
			centerDrawable = getContext().getResources().getDrawable(
					R.drawable.wheel_val);
		}

		if (topShadow == null) {
			topShadow = new GradientDrawable(Orientation.TOP_BOTTOM,
					SHADOWS_COLORS);
		}

		if (bottomShadow == null) {
			bottomShadow = new GradientDrawable(Orientation.BOTTOM_TOP,
					SHADOWS_COLORS);
		}

		setBackgroundResource(R.drawable.wheel_bg);
	}

	
	/**
	 * 计算layout所需的高度
	 * @param layout
	 * @return
	 */
	private int getDesiredHeight(Layout layout) {
		if (layout == null) {
			return 0;
		}

		int desired = getItemHeight() * visibleItems - ITEM_OFFSET * 2
				- ADDITIONAL_ITEM_HEIGHT;
		
		desired = Math.max(desired,getSuggestedMinimumHeight());
		return desired;
	}
	
	
	/**
	 * 通过index得到text
	 * @param index
	 * @return
	 */
	private String getTextItem(int index){
		if(adapter == null || adapter.getItemsCount() == 0){
			return null;
		}
		int count = adapter.getItemsCount();
		if((index < 0 || index >= count) && !isCyclic){
			return null;
		}else{
			while(index < 0){
				index += count;
			}
		}
		index %= count;
		return adapter.getItem(index);
	}
	
	/**
	 * 根据当前值构建text
	 * 
	 * @param useCurrentValue
	 * @return the text
	 */
	private String buildText(boolean useCurrentValue) {
		StringBuilder itemsText = new StringBuilder();
		int addItems = visibleItems / 2 + 1;

		for (int i = currentItem - addItems; i <= currentItem + addItems; i++) {
			if (useCurrentValue || i != currentItem) {
				String text = getTextItem(i);
				if (text != null) {
					itemsText.append(text);
				}
			}
			if (i < currentItem + addItems) {
				itemsText.append("\n");
			}
		}
		
		return itemsText.toString();
	}

	/**
	 * 返回可以表示的item的最大长度
	 * @return the max length
	 */
	private int getMaxTextLength() {
		WheelAdapter adapter = getAdapter();
		if (adapter == null) {
			return 0;
		}
		
		int adapterLength = adapter.getMaximumLength();
		if (adapterLength > 0) {
			return adapterLength;
		}

		String maxText = null;
		int addItems = visibleItems / 2;
		for (int i = Math.max(currentItem - addItems, 0);
				i < Math.min(currentItem + visibleItems, adapter.getItemsCount()); i++) {
			String text = adapter.getItem(i);
			if (text != null && (maxText == null || maxText.length() < text.length())) {
				maxText = text;
			}
		}

		return maxText != null ? maxText.length() : 0;
	}

	/**
	 * 返回滚轮item的高度
	 * @return the item height
	 */
	private int getItemHeight() {
		if (itemHeight != 0) {
			return itemHeight;
		} else if (itemsLayout != null && itemsLayout.getLineCount() > 2) {
			itemHeight = itemsLayout.getLineTop(2) - itemsLayout.getLineTop(1);
			return itemHeight;
		}
		
		return getHeight() / visibleItems;
	}

	/**
	 * 计算控制宽度和创建text布局
	 * @param widthSize the input layout width
	 * @param mode the layout mode
	 * @return the calculated control width
	 */
	private int calculateLayoutWidth(int widthSize, int mode) {
		initResourceIfNecessary();

		int width = widthSize;

		int maxLength = getMaxTextLength();
		if (maxLength > 0) {
			float textWidth = FloatMath.ceil(Layout.getDesiredWidth("0", itemsPaint));
			itemsWidth = (int) (maxLength * textWidth);
		} else {
			itemsWidth = 0;
		}
		itemsWidth += ADDITIONAL_ITEMS_SPACE; // make it some more

		labelWidth = 0;
		if (label != null && label.length() > 0) {
			labelWidth = (int) FloatMath.ceil(Layout.getDesiredWidth(label, valuePaint));
		}

		boolean recalculate = false;
		if (mode == MeasureSpec.EXACTLY) {
			width = widthSize;
			recalculate = true;
		} else {
			width = itemsWidth + labelWidth + 2 * PADDING;
			if (labelWidth > 0) {
				width += LABEL_OFFSET;
			}

			// Check against our minimum width
			width = Math.max(width, getSuggestedMinimumWidth());

			if (mode == MeasureSpec.AT_MOST && widthSize < width) {
				width = widthSize;
				recalculate = true;
			}
		}

		if (recalculate) {
			// recalculate width
			int pureWidth = width - LABEL_OFFSET - 2 * PADDING;
			if (pureWidth <= 0) {
				itemsWidth = labelWidth = 0;
			}
			if (labelWidth > 0) {
				double newWidthItems = (double) itemsWidth * pureWidth
						/ (itemsWidth + labelWidth);
				itemsWidth = (int) newWidthItems;
				labelWidth = pureWidth - itemsWidth;
			} else {
				itemsWidth = pureWidth + LABEL_OFFSET; // no label
			}
		}

		if (itemsWidth > 0) {
			createLayouts(itemsWidth, labelWidth);
		}

		return width;
	}

	/**
	 * 创建布局
	 * @param widthItems width of items layout
	 * @param widthLabel width of label layout
	 */
	private void createLayouts(int widthItems, int widthLabel) {
		if (itemsLayout == null || itemsLayout.getWidth() > widthItems) {
			itemsLayout = new StaticLayout(buildText(isScrollingPerformed), itemsPaint, widthItems,
					widthLabel > 0 ? Layout.Alignment.ALIGN_OPPOSITE : Layout.Alignment.ALIGN_CENTER,
					1, ADDITIONAL_ITEM_HEIGHT, false);
		} else {
			itemsLayout.increaseWidthTo(widthItems);
		}

		if (!isScrollingPerformed && (valueLayout == null || valueLayout.getWidth() > widthItems)) {
			String text = getAdapter() != null ? getAdapter().getItem(currentItem) : null;
			valueLayout = new StaticLayout(text != null ? text : "",
					valuePaint, widthItems, widthLabel > 0 ?
							Layout.Alignment.ALIGN_OPPOSITE : Layout.Alignment.ALIGN_CENTER,
							1, ADDITIONAL_ITEM_HEIGHT, false);
		} else if (isScrollingPerformed) {
			valueLayout = null;
		} else {
			valueLayout.increaseWidthTo(widthItems);
		}

		if (widthLabel > 0) {
			if (labelLayout == null || labelLayout.getWidth() > widthLabel) {
				labelLayout = new StaticLayout(label, valuePaint,
						widthLabel, Layout.Alignment.ALIGN_NORMAL, 1,
						ADDITIONAL_ITEM_HEIGHT, false);
			} else {
				labelLayout.increaseWidthTo(widthLabel);
			}
		}
	}

	@Override
	protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
		int widthMode = MeasureSpec.getMode(widthMeasureSpec);
		int heightMode = MeasureSpec.getMode(heightMeasureSpec);
		int widthSize = MeasureSpec.getSize(widthMeasureSpec);
		int heightSize = MeasureSpec.getSize(heightMeasureSpec);

		int width = calculateLayoutWidth(widthSize, widthMode);

		int height;
		if (heightMode == MeasureSpec.EXACTLY) {
			height = heightSize;
		} else {
			height = getDesiredHeight(itemsLayout);

			if (heightMode == MeasureSpec.AT_MOST) {
				height = Math.min(height, heightSize);
			}
		}

		setMeasuredDimension(width, height);
	}

	@Override
	protected void onDraw(Canvas canvas) {
		super.onDraw(canvas);
		
		if (itemsLayout == null) {
			if (itemsWidth == 0) {
				calculateLayoutWidth(getWidth(), MeasureSpec.EXACTLY);
			} else {
				createLayouts(itemsWidth, labelWidth);
			}
		}

		if (itemsWidth > 0) {
			canvas.save();
			// Skip padding space and hide a part of top and bottom items
			canvas.translate(PADDING, -ITEM_OFFSET);
			drawItems(canvas);
			drawValue(canvas);
			canvas.restore();
		}

		drawCenterRect(canvas);
		drawShadows(canvas);
	}

	/**
	 * 在顶部和底部画阴影的控制
	 * @param canvas the canvas for drawing
	 */
	private void drawShadows(Canvas canvas) {
		topShadow.setBounds(0, 0, getWidth(), getHeight() / visibleItems);
		topShadow.draw(canvas);

		bottomShadow.setBounds(0, getHeight() - getHeight() / visibleItems,
				getWidth(), getHeight());
		bottomShadow.draw(canvas);
	}

	/**
	 * 画value和标签的布局
	 * @param canvas the canvas for drawing
	 */
	private void drawValue(Canvas canvas) {
		valuePaint.setColor(VALUE_TEXT_COLOR);
		valuePaint.drawableState = getDrawableState();

		Rect bounds = new Rect();
		itemsLayout.getLineBounds(visibleItems / 2, bounds);

		// draw label
		if (labelLayout != null) {
			canvas.save();
			canvas.translate(itemsLayout.getWidth() + LABEL_OFFSET, bounds.top);
			labelLayout.draw(canvas);
			canvas.restore();
		}

		// draw current value
		if (valueLayout != null) {
			canvas.save();
			canvas.translate(0, bounds.top + scrollingOffset);
			valueLayout.draw(canvas);
			canvas.restore();
		}
	}

	/**
	 * 画items
	 * @param canvas the canvas for drawing
	 */
	private void drawItems(Canvas canvas) {
		canvas.save();
		
		int top = itemsLayout.getLineTop(1);
		canvas.translate(0, - top + scrollingOffset);
		
		itemsPaint.setColor(ITEMS_TEXT_COLOR);
		itemsPaint.drawableState = getDrawableState();
		itemsLayout.draw(canvas);
		
		canvas.restore();
	}

	/**
	 * 画当前值的矩形
	 * @param canvas the canvas for drawing
	 */
	private void drawCenterRect(Canvas canvas) {
		int center = getHeight() / 2;
		int offset = getItemHeight() / 2;
		centerDrawable.setBounds(0, center - offset, getWidth(), center + offset);
		centerDrawable.draw(canvas);
	}

	@Override
	public boolean onTouchEvent(MotionEvent event) {
		WheelAdapter adapter = getAdapter();
		if (adapter == null) {
			return true;
		}
		
			if (!gestureDetector.onTouchEvent(event) && event.getAction() == MotionEvent.ACTION_UP) {
			justify();
		}
		return true;
	}
	
	/**
	 * 滚动滚轮
	 * @param delta the scrolling value
	 */
	private void doScroll(int delta) {
		scrollingOffset += delta;
		
		int count = scrollingOffset / getItemHeight();
		int pos = currentItem - count;
		if (isCyclic && adapter.getItemsCount() > 0) {
			// fix position by rotating
			while (pos < 0) {
				pos += adapter.getItemsCount();
			}
			pos %= adapter.getItemsCount();
		} else if (isScrollingPerformed) {
			// 
			if (pos < 0) {
				count = currentItem;
				pos = 0;
			} else if (pos >= adapter.getItemsCount()) {
				count = currentItem - adapter.getItemsCount() + 1;
				pos = adapter.getItemsCount() - 1;
			}
		} else {
			// fix position
			pos = Math.max(pos, 0);
			pos = Math.min(pos, adapter.getItemsCount() - 1);
		}
		
		int offset = scrollingOffset;
		if (pos != currentItem) {
			setCurrentItem(pos, false);
		} else {
			invalidate();
		}
		
		// update offset
		scrollingOffset = offset - count * getItemHeight();
		if (scrollingOffset > getHeight()) {
			scrollingOffset = scrollingOffset % getHeight() + getHeight();
		}
	}
	
	// gesture listener
	private SimpleOnGestureListener gestureListener = new SimpleOnGestureListener() {
		public boolean onDown(MotionEvent e) {
			if (isScrollingPerformed) {
				scroller.forceFinished(true);
				clearMessages();
				return true;
			}
			return false;
		}
		
		public boolean onScroll(MotionEvent e1, MotionEvent e2, float distanceX, float distanceY) {
			startScrolling();
			doScroll((int)-distanceY);
			return true;
		}
		
		public boolean onFling(MotionEvent e1, MotionEvent e2, float velocityX, float velocityY) {
			lastScrollY = currentItem * getItemHeight() + scrollingOffset;
			int maxY = isCyclic ? 0x7FFFFFFF : adapter.getItemsCount() * getItemHeight();
			int minY = isCyclic ? -maxY : 0;
			scroller.fling(0, lastScrollY, 0, (int) -velocityY / 2, 0, 0, minY, maxY);
			setNextMessage(MESSAGE_SCROLL);
			return true;
		}
	};


	// Messages
	private final int MESSAGE_SCROLL = 0;
	private final int MESSAGE_JUSTIFY = 1;
	
	/**
	 * Set next message to queue. Clears queue before.
	 * 
	 * @param message the message to set
	 */
	private void setNextMessage(int message) {
		clearMessages();
		animationHandler.sendEmptyMessage(message);
	}

	/**
	 * Clears messages from queue
	 */
	private void clearMessages() {
		animationHandler.removeMessages(MESSAGE_SCROLL);
		animationHandler.removeMessages(MESSAGE_JUSTIFY);
	}
	
	// animation handler
	private Handler animationHandler = new Handler() {
		public void handleMessage(Message msg) {
			scroller.computeScrollOffset();
			int currY = scroller.getCurrY();
			int delta = lastScrollY - currY;
			lastScrollY = currY;
			if (delta != 0) {
				doScroll(delta);
			}
			
			// scrolling is not finished when it comes to final Y
			// so, finish it manually 
			if (Math.abs(currY - scroller.getFinalY()) < MIN_DELTA_FOR_SCROLLING) {
				currY = scroller.getFinalY();
				scroller.forceFinished(true);
			}
			if (!scroller.isFinished()) {
				animationHandler.sendEmptyMessage(msg.what);
			} else if (msg.what == MESSAGE_SCROLL) {
				justify();
			} else {
				finishScrolling();
			}
		}
	};
	
	/**
	 * Justifies wheel
	 */
	private void justify() {
		if (adapter == null) {
			return;
		}
		
		lastScrollY = 0;
		int offset = scrollingOffset;
		int itemHeight = getItemHeight();
		boolean needToIncrease = offset > 0 ? currentItem < adapter.getItemsCount() : currentItem > 0; 
		if ((isCyclic || needToIncrease) && Math.abs((float) offset) > (float) itemHeight / 2) {
			if (offset < 0)
				offset += itemHeight + MIN_DELTA_FOR_SCROLLING;
			else
				offset -= itemHeight + MIN_DELTA_FOR_SCROLLING;
		}
		if (Math.abs(offset) > MIN_DELTA_FOR_SCROLLING) {
			scroller.startScroll(0, 0, 0, offset, SCROLLING_DURATION);
			setNextMessage(MESSAGE_JUSTIFY);
		} else {
			finishScrolling();
		}
	}
	
	/**
	 * 开始滚动
	 */
	private void startScrolling() {
		if (!isScrollingPerformed) {
			isScrollingPerformed = true;
			notifyScrollingListenersAboutStart();
		}
	}

	/**
	 * 停止滚动
	 */
	void finishScrolling() {
		if (isScrollingPerformed) {
			notifyScrollingListenersAboutEnd();
			isScrollingPerformed = false;
		}
		invalidateLayouts();
		invalidate();
	}

	public void scroll(int itemsToScroll, int time) {
		scroller.forceFinished(true);

		lastScrollY = scrollingOffset;

		int offset = itemsToScroll * getItemHeight();

		scroller.startScroll(0, lastScrollY, 0, offset - lastScrollY, time);
		setNextMessage(MESSAGE_SCROLL);

		startScrolling();
	}

}

这个demo还是比较实用的，可以自行将自定义的view按照自己需要进行修改扩展来实现自己想要的功能，放在今后自己开发的项目中去，当做一个控件直接使用，很方便