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 Android教程網 >> Android技術 >> 關於Android編程 >> android 滾輪刻度尺的實現

android 滾輪刻度尺的實現

編輯：關於Android編程

遇到一個需求需要實現如下圖的效果：

vcPmtcS2q8730tTHsMO7xaq5/aOs0tTEv8ewxOO1xMTcwaajrM/rwcu8uNbWy7zCt7a8y8DU2sHLsOvCt8nPoaOxyMjnyc/D5rXEv8y2yM/fyOe6zsWqo6y7rLavtcTKsbry09a4w8jnus7FqqO7z8LD5rXEyv3X1tPWyOe6zsWqo7u/tMbwwLTP8dSyyKa1xNCnufu4w8jnus7FqqGjyrG85L30xsijrL7NwanN7cnPtcTKsbzkoaPDu9PQusO1xMu8wre+zbLOv7yx8MjLtcTPyLDJo6zLtcC00rLHyaOswb3M7MewuNW/tLn90ru49sjVxtrRodTxv9i8/qOsu7nT0NLUx7C/tLXE0ru49rfCSVBob25lufa2r7/YvP6jrNCnufvA4CYjMjAyODQ7o7o8L3A+CjxwPjxpbWcgc3JjPQ=="/uploadfile/Collfiles/20140902/20140902085811168.jpg" width="400" height="188" alt="\">\

本想找作者傲慢的上校交流下，但是時間比較緊，源碼都給了也不是很好意思。大致的浏覽了下，可能涉及下面幾個東西：

1、背景：這個用shape實現。之前有研究過，也用過，但是還沒實現過要求的效果；

2、刻度和數字：這個就不要亂想了，直接draw。相對來說還是比較簡單的，就是畫直線和數字；

3、滾動：滾動的時候不停的重繪實現一個滾動的效果。弄過，但是不確定實現的是啥樣的效果；

4、快速滾動：Scroller和VelocityTracker可能是需要用到的東西。幾乎完全沒弄過，騷年，學習吧（需求的要求中，這個優先級可以最低）；

5、需求：刻度的單位是可以變的，比如十格一個單位，或者兩格一個單位，在或者可以是任意的（這個前期思路沒想好，實現起來就困難了，最後只弄了兩種）。

其實，到了這一步基本上就已經可以實現了，看個最終效果先：

\


下面就一步一步來。在這之前還有個地方要說的，就是控件的接口：對外提供一個方法實現控件初始化和接收控件選擇的值：顯示的單位，最大值，最小值，當前值，回調接口。有了這些，先從最難的入手。首先，實現刻度和數字，並可以滑動。這個地方很關鍵，每個人有每個人的思路，而且思路的好壞直接影響到後面對不同單位的實現。目前的思路是根據當前顯示的數值mValue，從控件中間向兩邊畫刻度線，滑動的時候同時改變顯示的值mValue，不足最小刻度的四捨五入：

	@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);
	}

	/**
	 * 從中間往兩邊開始畫刻度線
	 * 
	 * @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();
	}
接著就是滑動的加速問題，這裡用到兩個類Scroller和VelocityTracker，關於這兩個類之後有機會會詳細介紹，這裡簡單提下：VelocityTracker的作用是在用戶加速滑動時計算該滑動多遠，拿到這個之後通過Scroller來執行滑動過程的計算，最後是真實的“移動”——根據mValue的值進行重繪： 

	@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;
			}
		}
	}
最後就是圓圈背景的實現。這個用shape來做，可以使用setBackgroundDrawable()來做，也可以在draw中進行直接繪制，效果相同。其他的還有一些細節問題，比如滑動時刻度線超過邊界，滑動距離大時候顯示不完整等問題，這個只有做了才會發現。下面是shape背景的代碼：
用代碼可以這樣寫： 

	private GradientDrawable createBackground() {
		float strokeWidth = 4 * mDensity; // 邊框寬度
		float roundRadius = 6 * mDensity; // 圓角半徑
		int strokeColor = Color.parseColor("#FF666666");// 邊框顏色
		// int fillColor = Color.parseColor("#DFDFE0");// 內部填充顏色
		
		setPadding((int)strokeWidth, (int)strokeWidth, (int)strokeWidth, 0);

		int colors[] = { 0xFF999999, 0xFFFFFFFF, 0xFF999999 };// 分別為開始顏色，中間夜色，結束顏色
		GradientDrawable bgDrawable = new GradientDrawable(GradientDrawable.Orientation.LEFT_RIGHT, colors);// 創建drawable
		// bgDrawable.setColor(fillColor);
		bgDrawable.setCornerRadius(roundRadius);
		bgDrawable.setStroke((int)strokeWidth, strokeColor);
		// setBackgroundDrawable(gd);
		return bgDrawable;
	}
最後在來貼一下完整的代碼： 

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;

/**
 * 卷尺控件類。由於時間比較緊，只有下班後有時間，因此只實現了基本功能。

 * 細節問題包括滑動過程中widget邊緣的刻度顯示問題等

 * 
 * 周末有時間會繼續更新

 * 
 * @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; // 邊框寬度
		float roundRadius = 6 * mDensity; // 圓角半徑
		int strokeColor = Color.parseColor("#FF666666");// 邊框顏色
		// int fillColor = Color.parseColor("#DFDFE0");// 內部填充顏色
		
		setPadding((int)strokeWidth, (int)strokeWidth, (int)strokeWidth, 0);

		int colors[] = { 0xFF999999, 0xFFFFFFFF, 0xFF999999 };// 分別為開始顏色，中間夜色，結束顏色
		GradientDrawable bgDrawable = new GradientDrawable(GradientDrawable.Orientation.LEFT_RIGHT, colors);// 創建drawable
		// bgDrawable.setColor(fillColor);
		bgDrawable.setCornerRadius(roundRadius);
		bgDrawable.setStroke((int)strokeWidth, strokeColor);
		// setBackgroundDrawable(gd);
		return bgDrawable;
	}

	/**
	 * 
	 * 考慮可擴展，但是時間緊迫，只可以支持兩種類型效果圖中兩種類型
	 * 
	 * @param value
	 *            初始值
	 * @param maxValue
	 *            最大值
	 * @param model
	 *            刻度盤精度：

	 *            {@link MOD_TYPE_HALF}

	 *            {@link MOD_TYPE_ONE}

	 */
	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();
	}

	/**
	 * 設置用於接收結果的監聽器
	 * 
	 * @param listener
	 */
	public void setValueChangeListener(OnValueChangeListener listener) {
		mListener = listener;
	}

	/**
	 * 獲取當前刻度值
	 * 
	 * @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);
	}

	/**
	 * 從中間往兩邊開始畫刻度線
	 * 
	 * @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();
	}

	/**
	 * 計算沒有數字顯示位置的輔助方法
	 * 
	 * @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;
	}

	/**
	 * 畫中間的紅色指示線、陰影等。指示線兩端簡單的用了兩個矩形代替
	 * 
	 * @param canvas
	 */
	private void drawMiddleLine(Canvas canvas) {
		// TOOD 常量太多，暫時放這，最終會放在類的開始，放遠了怕很快忘記
		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 橢圓
		// 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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