本文主要是介绍android的尺子滚动功能 RulerWheel，希望对大家解决编程问题提供一定的参考价值，需要的开发者们随着小编来一起学习吧！
一直想搞一个滚动的尺子功能，精力有限，又赖没去实现过！ 后来项目中有个类似的功能，前期做一些核心功能所以那个功能一直在使用替代方案，后期觉得实在看不下去了！想想还是需要解决一下这个功能！在网上找了一下类似功能，发现都不能满意！花了点时间研究了开源项目kankan.wheel.widget.WheelView @author Yuri Kanivets， 感觉原理差不多，不过WheelView 是垂直的选择器， 我需要的是可以水平滚动的尺子，而且我也不需要适配数据！ 砍掉了大部分！重新改造适合自己的需求功能
上效果图
第一张
贴上RulerWheel.java 部分源码（注. WheelScroller .java 和 WheelView.java 重新命名为 RulerWheel.java 和 WheelHorizontalScroller.java ）
一、首先是onTouchEvent事件、
public boolean onTouchEvent(MotionEvent event) {switch (event.getAction()) {case MotionEvent.ACTION_DOWN:lastTouchedX = event.getX(); scroller.forceFinished(true); clearMessages(); break; case MotionEvent.ACTION_MOVE:// perform scrolling int distanceX = (int) (event.getX() - lastTouchedX); if (distanceX != 0) {startScrolling(); listener.onScroll(distanceX); lastTouchedX = event.getX(); }break; }if (!gestureDetector.onTouchEvent(event) && event.getAction() == MotionEvent.ACTION_UP) {justify(); }return true; }
ACTION_MOVE处理了每次滑动的偏移量，看下面doScroll
private void doScroll(int delta) {scrollingOffset += delta; int offsetCount = scrollingOffset / mLineDivder; if (0 != offsetCount) {// 显示在范围内 int oldValue = Math.min(Math.max(0, mCurrValue), mMaxValue); mCurrValue -= offsetCount; scrollingOffset -= offsetCount * mLineDivder; if (null != onWheelListener) {onWheelListener.onChanged(this, oldValue, Math.min(Math.max(0, mCurrValue), mMaxValue)); }}invalidate(); }
int distanceX 记录了X移动的偏移量， 根据移动的偏移量，计算偏移了n刻度
int offsetCount = scrollingOffset / mLineDivder; (mLineDivder 刻度之间间隔，mCurrValue 当前刻度值)
if (0 != offsetCount) {
....
更新当前刻度值
更新当前偏移量
}
二、GestureDetector事件
public boolean onFling(MotionEvent e1, MotionEvent e2, float velocityX, float velocityY) {lastScrollX = 0; // final int maxX = 0x7FFFFFFF; // final int minX = -maxX; scroller.fling(0, lastScrollX, (int) -velocityX, 0, -0x7FFFFFFF, 0x7FFFFFFF, 0, 0); setNextMessage(MESSAGE_SCROLL); return true; }
手势中做了一次scroller.fling处理Handler重复回调自身msg, 直到fling位移路径全部完成
// animation handler private Handler animationHandler = new Handler(new Handler.Callback() {@Override public boolean handleMessage(Message msg) {scroller.computeScrollOffset(); int currX = scroller.getCurrX(); int delta = lastScrollX - currX; lastScrollX = currX; if (delta != 0) {listener.onScroll(delta); }// scrolling is not finished when it comes to final Y // so, finish it manually if (Math.abs(currX - scroller.getFinalX()) < MIN_DELTA_FOR_SCROLLING) {lastScrollX = scroller.getFinalX(); scroller.forceFinished(true); }if (!scroller.isFinished()) {animationHandler.sendEmptyMessage(msg.what); } else if (msg.what == MESSAGE_SCROLL) {justify(); } else {finishScrolling(); }return true; } });
三、绘制刻度内容
绘制刻度从中间点开始，左右各绘制一半内容
/** * @param canvas * @param rWidth 显示宽度 * @param rHeight 显示高度 * @param ry 线y坐标 */ private void drawScaleLine(Canvas canvas, int rWidth, int rHeight, int ry) {// 根据间隔计算当前一半宽度的个数+偏移2个 final int halfCount = (int) Math.ceil(rWidth / 2f / mLineDivder) + 2; final int distanceX = scrollingOffset; final int currValue = mCurrValue; int value; float xPosition; for (int i = 0; i < halfCount; i++) {// right xPosition = rWidth / 2f + i * mLineDivder + distanceX; value = currValue + i; if (xPosition <= rWidth && value >= 0 && value <= mMaxValue) {if (value % mModType == 0) {if (mModType == MOD_TYPE_HALF) {linePaint.setColor(mLineColorMax); canvas.drawLine(xPosition, ry, xPosition, ry + mLineHeighMax, linePaint); if (isScaleValue) {canvas.drawText(String.valueOf(value / 2), xPosition, rHeight - mTpDesiredWidth, textPaint); }} else if (mModType == MOD_TYPE_SCALE) {if (value % (MOD_TYPE_SCALE * 2) == 0) {linePaint.setColor(mLineColorMax); canvas.drawLine(xPosition, ry, xPosition, ry + mLineHeighMax, linePaint); if (isScaleValue) {canvas.drawText(String.valueOf(value), xPosition, rHeight - mTpDesiredWidth, textPaint); }} else {linePaint.setColor(mLineColorMid); canvas.drawLine(xPosition, ry, xPosition, ry + mLineHeighMid, linePaint); }}} else {linePaint.setColor(mLineColorMin); canvas.drawLine(xPosition, ry, xPosition, ry + mLineHeighMin, linePaint); }}// left xPosition = rWidth / 2f - i * mLineDivder + distanceX; value = currValue - i; if (xPosition > getPaddingLeft() && value >= 0 && value <= mMaxValue) {if (value % mModType == 0) {if (mModType == MOD_TYPE_HALF) {linePaint.setColor(mLineColorMax); canvas.drawLine(xPosition, ry, xPosition, ry + mLineHeighMax, linePaint); if (isScaleValue) {canvas.drawText(String.valueOf(value / 2), xPosition, rHeight - mTpDesiredWidth, textPaint); }} else if (mModType == MOD_TYPE_SCALE) {if (value % (MOD_TYPE_SCALE * 2) == 0) {linePaint.setColor(mLineColorMax); canvas.drawLine(xPosition, ry, xPosition, ry + mLineHeighMax, linePaint); if (isScaleValue) {canvas.drawText(String.valueOf(value), xPosition, rHeight - mTpDesiredWidth, textPaint); }} else {linePaint.setColor(mLineColorMid); canvas.drawLine(xPosition, ry, xPosition, ry + mLineHeighMid, linePaint); }}} else {linePaint.setColor(mLineColorMin); canvas.drawLine(xPosition, ry, xPosition, ry + mLineHeighMin, linePaint); }}} }
绘制的核心就是下面这几句
final int distanceX = scrollingOffset; x偏移量 final int currValue = mCurrValue; 当前刻度值
// right xPosition = rWidth / 2f + i * mLineDivder + distanceX; value = currValue + i;
...
// left xPosition = rWidth / 2f - i * mLineDivder + distanceX; value = currValue - i;
通过不断的doScroll( ** ) 函数，修正mCurrValue 和 scrollingOffset 的值 ，达到不断移动的效果
忘了上传源码附件，补充一下 源码附件RulerWheel
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