android 滚轮刻度尺的实现

浏览数：55 / 时间：2015年06月11日

遇到一个需求需要实现如下图的效果：

卷尺，通过左右滑动来选择不同的刻度值。这方面的东西以前没弄过，以目前你的能力，想了几种思路都死在了半路上。比如上面的刻度线如何弄，滑动的时候又该如何弄；下面的数字又如何弄；看起来像圆圈的效果该如何弄。时间紧迫，就俩晚上的时间。没有好的思路就参考别人的先吧，说来也巧，两天前刚看过一个日期选择控件，还有以前看的一个仿IPhone滚动控件，效果类似：

本想找作者傲慢的上校交流下，但是时间比较紧，源码都给了也不是很好意思。大致的浏览了下，可能涉及下面几个东西：

1、背景：这个用shape实现。之前有研究过，也用过，但是还没实现过要求的效果；

2、刻度和数字：这个就不要乱想了，直接draw。相对来说还是比较简单的，就是画直线和数字；

3、滚动：滚动的时候不停的重绘实现一个滚动的效果。弄过，但是不确定实现的是啥样的效果；

4、快速滚动：Scroller和VelocityTracker可能是需要用到的东西。几乎完全没弄过，骚年，学习吧（需求的要求中，这个优先级可以最低）；

5、需求：刻度的单位是可以变的，比如十格一个单位，或者两格一个单位，在或者可以是任意的（这个前期思路没想好，实现起来就困难了，最后只弄了两种）。

其实，到了这一步基本上就已经可以实现了，看个最终效果先：

下面就一步一步来。在这之前还有个地方要说的，就是控件的接口：对外提供一个方法实现控件初始化和接收控件选择的值：显示的单位，最大值，最小值，当前值，回调接口。有了这些，先从最难的入手。首先，实现刻度和数字，并可以滑动。这个地方很关键，每个人有每个人的思路，而且思路的好坏直接影响到后面对不同单位的实现。目前的思路是根据当前显示的数值mValue，从控件中间向两边画刻度线，滑动的时候同时改变显示的值mValue，不足最小刻度的四舍五入：

	@Override
	protected void onDraw(Canvas canvas) {
		super.onDraw(canvas);

		drawScaleLine(canvas);
		// drawWheel(canvas);
		drawMiddleLine(canvas);
	}

	private void drawWheel(Canvas canvas) {
		Drawable wheel = getResources().getDrawable(R.drawable.bg_wheel);
		wheel.setBounds(0, 0, getWidth(), getHeight());
		wheel.draw(canvas);
	}

	/**
	 * 从中间往两边开始画刻度线
	 * 
	 * @param canvas
	 */
	private void drawScaleLine(Canvas canvas) {
		canvas.save();

		Paint linePaint = new Paint();
		linePaint.setStrokeWidth(2);
		linePaint.setColor(Color.BLACK);

		TextPaint textPaint = new TextPaint(Paint.ANTI_ALIAS_FLAG);
		textPaint.setTextSize(TEXT_SIZE * mDensity);

		int width = mWidth, drawCount = 0;
		float xPosition = 0, textWidth = Layout.getDesiredWidth("0", textPaint);

		for (int i = 0; drawCount <= 4 * width; i++) {
			int numSize = String.valueOf(mValue + i).length();

			xPosition = (width / 2 - mMove) + i * mLineDivider * mDensity;
			if (xPosition + getPaddingRight() < mWidth) {
				if ((mValue + i) % mModType == 0) {
					canvas.drawLine(xPosition, getPaddingTop(), xPosition, mDensity * ITEM_MAX_HEIGHT, linePaint);

					if (mValue + i <= mMaxValue) {
						switch (mModType) {
						case MOD_TYPE_HALF:
							canvas.drawText(String.valueOf((mValue + i) / 2), countLeftStart(mValue + i, xPosition, textWidth), getHeight() - textWidth, textPaint);
							break;
						case MOD_TYPE_ONE:
							canvas.drawText(String.valueOf(mValue + i), xPosition - (textWidth * numSize / 2), getHeight() - textWidth, textPaint);
							break;

						default:
							break;
						}
					}
				} else {
					canvas.drawLine(xPosition, getPaddingTop(), xPosition, mDensity * ITEM_MIN_HEIGHT, linePaint);
				}
			}

			xPosition = (width / 2 - mMove) - i * mLineDivider * mDensity;
			if (xPosition > getPaddingLeft()) {
				if ((mValue - i) % mModType == 0) {
					canvas.drawLine(xPosition, getPaddingTop(), xPosition, mDensity * ITEM_MAX_HEIGHT, linePaint);

					if (mValue - i >= 0) {
						switch (mModType) {
						case MOD_TYPE_HALF:
							canvas.drawText(String.valueOf((mValue - i) / 2), countLeftStart(mValue - i, xPosition, textWidth), getHeight() - textWidth, textPaint);
							break;
						case MOD_TYPE_ONE:
							canvas.drawText(String.valueOf(mValue - i), xPosition - (textWidth * numSize / 2), getHeight() - textWidth, textPaint);
							break;

						default:
							break;
						}
					}
				} else {
					canvas.drawLine(xPosition, getPaddingTop(), xPosition, mDensity * ITEM_MIN_HEIGHT, linePaint);
				}
			}

			drawCount += 2 * mLineDivider * mDensity;
		}

		canvas.restore();
	}

接着就是滑动的加速问题，这里用到两个类Scroller和VelocityTracker，关于这两个类之后有机会会详细介绍，这里简单提下：VelocityTracker的作用是在用户加速滑动时计算该滑动多远，拿到这个之后通过Scroller来执行滑动过程的计算，最后是真实的“移动”——根据mValue的值进行重绘：

	@Override
	public boolean onTouchEvent(MotionEvent event) {
		int action = event.getAction();
		int xPosition = (int) event.getX();

		if (mVelocityTracker == null) {
			mVelocityTracker = VelocityTracker.obtain();
		}
		mVelocityTracker.addMovement(event);

		switch (action) {
		case MotionEvent.ACTION_DOWN:

			mScroller.forceFinished(true);

			mLastX = xPosition;
			mMove = 0;
			break;
		case MotionEvent.ACTION_MOVE:
			mMove += (mLastX - xPosition);
			changeMoveAndValue();
			break;
		case MotionEvent.ACTION_UP:
		case MotionEvent.ACTION_CANCEL:
			countMoveEnd();
			countVelocityTracker(event);
			return false;
			// break;
		default:
			break;
		}

		mLastX = xPosition;
		return true;
	}

	private void countVelocityTracker(MotionEvent event) {
		mVelocityTracker.computeCurrentVelocity(1000);
		float xVelocity = mVelocityTracker.getXVelocity();
		if (Math.abs(xVelocity) > mMinVelocity) {
			mScroller.fling(0, 0, (int) xVelocity, 0, Integer.MIN_VALUE, Integer.MAX_VALUE, 0, 0);
		}
	}

	private void changeMoveAndValue() {
		int tValue = (int) (mMove / (mLineDivider * mDensity));
		if (Math.abs(tValue) > 0) {
			mValue += tValue;
			mMove -= tValue * mLineDivider * mDensity;
			if (mValue <= 0 || mValue > mMaxValue) {
				mValue = mValue <= 0 ? 0 : mMaxValue;
				mMove = 0;
				mScroller.forceFinished(true);
			}
			notifyValueChange();
		}
		postInvalidate();
	}

	private void countMoveEnd() {
		int roundMove = Math.round(mMove / (mLineDivider * mDensity));
		mValue = mValue + roundMove;
		mValue = mValue <= 0 ? 0 : mValue;
		mValue = mValue > mMaxValue ? mMaxValue : mValue;

		mLastX = 0;
		mMove = 0;
		
		notifyValueChange();
		postInvalidate();
	}

	private void notifyValueChange() {
		if (null != mListener) {
			if (mModType == MOD_TYPE_ONE) {
				mListener.onValueChange(mValue);
			}
			if (mModType == MOD_TYPE_HALF) {
				mListener.onValueChange(mValue / 2f);
			}
		}
	}

	@Override
	public void computeScroll() {
		super.computeScroll();
		if (mScroller.computeScrollOffset()) {
			if (mScroller.getCurrX() == mScroller.getFinalX()) { // over
				countMoveEnd();
			} else {
				int xPosition = mScroller.getCurrX();
				mMove += (mLastX - xPosition);
				changeMoveAndValue();
				mLastX = xPosition;
			}
		}
	}

最后就是圆圈背景的实现。这个用shape来做，可以使用setBackgroundDrawable()来做，也可以在draw中进行直接绘制，效果相同。其他的还有一些细节问题，比如滑动时刻度线超过边界，滑动距离大时候显示不完整等问题，这个只有做了才会发现。下面是shape背景的代码：

<?xml version="1.0" encoding="utf-8"?>
<shape xmlns:android="http://schemas.android.com/apk/res/android"
    android:shape="rectangle" >

    <!-- two set color way -->
    <gradient
        android:angle="0"
        android:centerColor="#66FFFFFF"
        android:endColor="#66AAAAAA"
        android:startColor="#66AAAAAA" />

    <corners android:radius="6dp" />

    <stroke
        android:width="6dp"
        android:color="#FF666666" />

</shape>

用代码可以这样写：

	private GradientDrawable createBackground() {
		float strokeWidth = 4 * mDensity; // 边框宽度
		float roundRadius = 6 * mDensity; // 圆角半径
		int strokeColor = Color.parseColor("#FF666666");// 边框颜色
		// int fillColor = Color.parseColor("#DFDFE0");// 内部填充颜色
		
		setPadding((int)strokeWidth, (int)strokeWidth, (int)strokeWidth, 0);

		int colors[] = { 0xFF999999, 0xFFFFFFFF, 0xFF999999 };// 分别为开始颜色，中间夜色，结束颜色
		GradientDrawable bgDrawable = new GradientDrawable(GradientDrawable.Orientation.LEFT_RIGHT, colors);// 创建drawable
		// bgDrawable.setColor(fillColor);
		bgDrawable.setCornerRadius(roundRadius);
		bgDrawable.setStroke((int)strokeWidth, strokeColor);
		// setBackgroundDrawable(gd);
		return bgDrawable;
	}

最后在来贴一下完整的代码：

package com.ttdevs.wheel.widget;

import android.annotation.SuppressLint;
import android.content.Context;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Paint;
import android.graphics.drawable.Drawable;
import android.graphics.drawable.GradientDrawable;
import android.text.Layout;
import android.text.TextPaint;
import android.util.AttributeSet;
import android.view.MotionEvent;
import android.view.VelocityTracker;
import android.view.View;
import android.view.ViewConfiguration;
import android.widget.Scroller;

import com.ttdevs.wheel.R;

/**
 * 卷尺控件类。由于时间比较紧，只有下班后有时间，因此只实现了基本功能。<br>
 * 细节问题包括滑动过程中widget边缘的刻度显示问题等<br>
 * 
 * 周末有时间会继续更新<br>
 * 
 * @author ttdevs
 * @version create：2014年8月26日
 */
@SuppressLint("ClickableViewAccessibility")
public class TuneWheel extends View {

	public interface OnValueChangeListener {
		public void onValueChange(float value);
	}

	public static final int MOD_TYPE_HALF = 2;
	public static final int MOD_TYPE_ONE = 10;

	private static final int ITEM_HALF_DIVIDER = 40;
	private static final int ITEM_ONE_DIVIDER = 10;

	private static final int ITEM_MAX_HEIGHT = 50;
	private static final int ITEM_MIN_HEIGHT = 20;

	private static final int TEXT_SIZE = 18;

	private float mDensity;
	private int mValue = 50, mMaxValue = 100, mModType = MOD_TYPE_HALF, mLineDivider = ITEM_HALF_DIVIDER;
	// private int mValue = 50, mMaxValue = 500, mModType = MOD_TYPE_ONE,
	// mLineDivider = ITEM_ONE_DIVIDER;

	private int mLastX, mMove;
	private int mWidth, mHeight;

	private int mMinVelocity;
	private Scroller mScroller;
	private VelocityTracker mVelocityTracker;

	private OnValueChangeListener mListener;

	@SuppressWarnings("deprecation")
	public TuneWheel(Context context, AttributeSet attrs) {
		super(context, attrs);

		mScroller = new Scroller(getContext());
		mDensity = getContext().getResources().getDisplayMetrics().density;

		mMinVelocity = ViewConfiguration.get(getContext()).getScaledMinimumFlingVelocity();

		// setBackgroundResource(R.drawable.bg_wheel);
		setBackgroundDrawable(createBackground());
	}

	private GradientDrawable createBackground() {
		float strokeWidth = 4 * mDensity; // 边框宽度
		float roundRadius = 6 * mDensity; // 圆角半径
		int strokeColor = Color.parseColor("#FF666666");// 边框颜色
		// int fillColor = Color.parseColor("#DFDFE0");// 内部填充颜色
		
		setPadding((int)strokeWidth, (int)strokeWidth, (int)strokeWidth, 0);

		int colors[] = { 0xFF999999, 0xFFFFFFFF, 0xFF999999 };// 分别为开始颜色，中间夜色，结束颜色
		GradientDrawable bgDrawable = new GradientDrawable(GradientDrawable.Orientation.LEFT_RIGHT, colors);// 创建drawable
		// bgDrawable.setColor(fillColor);
		bgDrawable.setCornerRadius(roundRadius);
		bgDrawable.setStroke((int)strokeWidth, strokeColor);
		// setBackgroundDrawable(gd);
		return bgDrawable;
	}

	/**
	 * 
	 * 考虑可扩展，但是时间紧迫，只可以支持两种类型效果图中两种类型
	 * 
	 * @param value
	 *            初始值
	 * @param maxValue
	 *            最大值
	 * @param model
	 *            刻度盘精度：<br>
	 *            {@link MOD_TYPE_HALF}<br>
	 *            {@link MOD_TYPE_ONE}<br>
	 */
	public void initViewParam(int defaultValue, int maxValue, int model) {
		switch (model) {
		case MOD_TYPE_HALF:
			mModType = MOD_TYPE_HALF;
			mLineDivider = ITEM_HALF_DIVIDER;
			mValue = defaultValue * 2;
			mMaxValue = maxValue * 2;
			break;
		case MOD_TYPE_ONE:
			mModType = MOD_TYPE_ONE;
			mLineDivider = ITEM_ONE_DIVIDER;
			mValue = defaultValue;
			mMaxValue = maxValue;
			break;

		default:
			break;
		}
		invalidate();

		mLastX = 0;
		mMove = 0;
		notifyValueChange();
	}

	/**
	 * 设置用于接收结果的监听器
	 * 
	 * @param listener
	 */
	public void setValueChangeListener(OnValueChangeListener listener) {
		mListener = listener;
	}

	/**
	 * 获取当前刻度值
	 * 
	 * @return
	 */
	public float getValue() {
		return mValue;
	}

	@Override
	protected void onLayout(boolean changed, int left, int top, int right, int bottom) {
		mWidth = getWidth();
		mHeight = getHeight();
		super.onLayout(changed, left, top, right, bottom);
	}

	@Override
	protected void onDraw(Canvas canvas) {
		super.onDraw(canvas);

		drawScaleLine(canvas);
		// drawWheel(canvas);
		drawMiddleLine(canvas);
	}

	private void drawWheel(Canvas canvas) {
		Drawable wheel = getResources().getDrawable(R.drawable.bg_wheel);
		wheel.setBounds(0, 0, getWidth(), getHeight());
		wheel.draw(canvas);
	}

	/**
	 * 从中间往两边开始画刻度线
	 * 
	 * @param canvas
	 */
	private void drawScaleLine(Canvas canvas) {
		canvas.save();

		Paint linePaint = new Paint();
		linePaint.setStrokeWidth(2);
		linePaint.setColor(Color.BLACK);

		TextPaint textPaint = new TextPaint(Paint.ANTI_ALIAS_FLAG);
		textPaint.setTextSize(TEXT_SIZE * mDensity);

		int width = mWidth, drawCount = 0;
		float xPosition = 0, textWidth = Layout.getDesiredWidth("0", textPaint);

		for (int i = 0; drawCount <= 4 * width; i++) {
			int numSize = String.valueOf(mValue + i).length();

			xPosition = (width / 2 - mMove) + i * mLineDivider * mDensity;
			if (xPosition + getPaddingRight() < mWidth) {
				if ((mValue + i) % mModType == 0) {
					canvas.drawLine(xPosition, getPaddingTop(), xPosition, mDensity * ITEM_MAX_HEIGHT, linePaint);

					if (mValue + i <= mMaxValue) {
						switch (mModType) {
						case MOD_TYPE_HALF:
							canvas.drawText(String.valueOf((mValue + i) / 2), countLeftStart(mValue + i, xPosition, textWidth), getHeight() - textWidth, textPaint);
							break;
						case MOD_TYPE_ONE:
							canvas.drawText(String.valueOf(mValue + i), xPosition - (textWidth * numSize / 2), getHeight() - textWidth, textPaint);
							break;

						default:
							break;
						}
					}
				} else {
					canvas.drawLine(xPosition, getPaddingTop(), xPosition, mDensity * ITEM_MIN_HEIGHT, linePaint);
				}
			}

			xPosition = (width / 2 - mMove) - i * mLineDivider * mDensity;
			if (xPosition > getPaddingLeft()) {
				if ((mValue - i) % mModType == 0) {
					canvas.drawLine(xPosition, getPaddingTop(), xPosition, mDensity * ITEM_MAX_HEIGHT, linePaint);

					if (mValue - i >= 0) {
						switch (mModType) {
						case MOD_TYPE_HALF:
							canvas.drawText(String.valueOf((mValue - i) / 2), countLeftStart(mValue - i, xPosition, textWidth), getHeight() - textWidth, textPaint);
							break;
						case MOD_TYPE_ONE:
							canvas.drawText(String.valueOf(mValue - i), xPosition - (textWidth * numSize / 2), getHeight() - textWidth, textPaint);
							break;

						default:
							break;
						}
					}
				} else {
					canvas.drawLine(xPosition, getPaddingTop(), xPosition, mDensity * ITEM_MIN_HEIGHT, linePaint);
				}
			}

			drawCount += 2 * mLineDivider * mDensity;
		}

		canvas.restore();
	}

	/**
	 * 计算没有数字显示位置的辅助方法
	 * 
	 * @param value
	 * @param xPosition
	 * @param textWidth
	 * @return
	 */
	private float countLeftStart(int value, float xPosition, float textWidth) {
		float xp = 0f;
		if (value < 20) {
			xp = xPosition - (textWidth * 1 / 2);
		} else {
			xp = xPosition - (textWidth * 2 / 2);
		}
		return xp;
	}

	/**
	 * 画中间的红色指示线、阴影等。指示线两端简单的用了两个矩形代替
	 * 
	 * @param canvas
	 */
	private void drawMiddleLine(Canvas canvas) {
		// TOOD 常量太多，暂时放这，最终会放在类的开始，放远了怕很快忘记
		int gap = 12, indexWidth = 8, indexTitleWidth = 24, indexTitleHight = 10, shadow = 6;
		String color = "#66999999";

		canvas.save();

		Paint redPaint = new Paint();
		redPaint.setStrokeWidth(indexWidth);
		redPaint.setColor(Color.RED);
		canvas.drawLine(mWidth / 2, 0, mWidth / 2, mHeight, redPaint);

		Paint ovalPaint = new Paint();
		ovalPaint.setColor(Color.RED);
		ovalPaint.setStrokeWidth(indexTitleWidth);
		canvas.drawLine(mWidth / 2, 0, mWidth / 2, indexTitleHight, ovalPaint);
		canvas.drawLine(mWidth / 2, mHeight - indexTitleHight, mWidth / 2, mHeight, ovalPaint);

		// RectF ovalRectF = new RectF(mWidth / 2 - 10, 0, mWidth / 2 + 10, 4 *
		// mDensity); //TODO 椭圆
		// canvas.drawOval(ovalRectF, ovalPaint);
		// ovalRectF.set(mWidth / 2 - 10, mHeight - 8 * mDensity, mWidth / 2 +
		// 10, mHeight); //TODO

		Paint shadowPaint = new Paint();
		shadowPaint.setStrokeWidth(shadow);
		shadowPaint.setColor(Color.parseColor(color));
		canvas.drawLine(mWidth / 2 + gap, 0, mWidth / 2 + gap, mHeight, shadowPaint);

		canvas.restore();
	}

	@Override
	public boolean onTouchEvent(MotionEvent event) {
		int action = event.getAction();
		int xPosition = (int) event.getX();

		if (mVelocityTracker == null) {
			mVelocityTracker = VelocityTracker.obtain();
		}
		mVelocityTracker.addMovement(event);

		switch (action) {
		case MotionEvent.ACTION_DOWN:

			mScroller.forceFinished(true);

			mLastX = xPosition;
			mMove = 0;
			break;
		case MotionEvent.ACTION_MOVE:
			mMove += (mLastX - xPosition);
			changeMoveAndValue();
			break;
		case MotionEvent.ACTION_UP:
		case MotionEvent.ACTION_CANCEL:
			countMoveEnd();
			countVelocityTracker(event);
			return false;
			// break;
		default:
			break;
		}

		mLastX = xPosition;
		return true;
	}

	private void countVelocityTracker(MotionEvent event) {
		mVelocityTracker.computeCurrentVelocity(1000);
		float xVelocity = mVelocityTracker.getXVelocity();
		if (Math.abs(xVelocity) > mMinVelocity) {
			mScroller.fling(0, 0, (int) xVelocity, 0, Integer.MIN_VALUE, Integer.MAX_VALUE, 0, 0);
		}
	}

	private void changeMoveAndValue() {
		int tValue = (int) (mMove / (mLineDivider * mDensity));
		if (Math.abs(tValue) > 0) {
			mValue += tValue;
			mMove -= tValue * mLineDivider * mDensity;
			if (mValue <= 0 || mValue > mMaxValue) {
				mValue = mValue <= 0 ? 0 : mMaxValue;
				mMove = 0;
				mScroller.forceFinished(true);
			}
			notifyValueChange();
		}
		postInvalidate();
	}

	private void countMoveEnd() {
		int roundMove = Math.round(mMove / (mLineDivider * mDensity));
		mValue = mValue + roundMove;
		mValue = mValue <= 0 ? 0 : mValue;
		mValue = mValue > mMaxValue ? mMaxValue : mValue;

		mLastX = 0;
		mMove = 0;

		notifyValueChange();
		postInvalidate();
	}

	private void notifyValueChange() {
		if (null != mListener) {
			if (mModType == MOD_TYPE_ONE) {
				mListener.onValueChange(mValue);
			}
			if (mModType == MOD_TYPE_HALF) {
				mListener.onValueChange(mValue / 2f);
			}
		}
	}

	@Override
	public void computeScroll() {
		super.computeScroll();
		if (mScroller.computeScrollOffset()) {
			if (mScroller.getCurrX() == mScroller.getFinalX()) { // over
				countMoveEnd();
			} else {
				int xPosition = mScroller.getCurrX();
				mMove += (mLastX - xPosition);
				changeMoveAndValue();
				mLastX = xPosition;
			}
		}
	}
}

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