Android实现滚动刻度尺效果

protected void init(AttributeSet attrs) {  
 // 获取自定义属性  
 TypedArray ta = getContext().obtainStyledAttributes(attrs, ATTR);  
 mMin = ta.getInteger(LF_SCALE_MIN, 0);  
 mMax = ta.getInteger(LF_SCALE_MAX, 200);  
 mScaleMargin = ta.getDimensionPixelOffset(LF_SCALE_MARGIN, 15);  
 mScaleHeight = ta.getDimensionPixelOffset(LF_SCALE_HEIGHT, 20);  
 ta.recycle();  
 mScroller = new Scroller(getContext());  
}

@Override
protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
 int height=MeasureSpec.makeMeasureSpec(mRectHeight, MeasureSpec.AT_MOST);  
 super.onMeasure(widthMeasureSpec, height);    
 mScaleScrollViewRange = getMeasuredWidth();  
 mTempScale = mScaleScrollViewRange / mScaleMargin / 2 + mMin;  
 mMidCountScale = mScaleScrollViewRange / mScaleMargin / 2 + mMin;
}

protected void onDrawScale(Canvas canvas, Paint paint) {  
 paint.setTextSize(mRectHeight / 4);
 for (int i = 0, k = mMin; i <= mMax - mMin; i++) {
   if (i % 10 == 0) { 
     //整值
     canvas.drawLine(i * mScaleMargin, mRectHeight, i * mScaleMargin, mRectHeight - mScaleMaxHeight, paint); 
     //整值文字
     canvas.drawText(String.valueOf(k), i * mScaleMargin, mRectHeight - mScaleMaxHeight - 20, paint);
     k += 10;
   } else {
     canvas.drawLine(i * mScaleMargin, mRectHeight, i * mScaleMargin, mRectHeight - mScaleHeight, paint); 
   }
 }
}

protected void onDrawPointer(Canvas canvas, Paint paint) {
 paint.setColor(Color.RED);
 //每一屏幕刻度的个数/2
 int countScale = mScaleScrollViewRange / mScaleMargin / 2;
 //根据滑动的距离，计算指针的位置【指针始终位于屏幕中间】
 int finalX = mScroller.getFinalX();
 //滑动的刻度
 int tmpCountScale = (int) Math.rint((double) finalX / (double) mScaleMargin);//四舍五入取整
 //总刻度
 mCountScale = tmpCountScale + countScale + mMin;
 if (mScrollListener != null) { //回调方法
   mScrollListener.onScaleScroll(mCountScale);
 }
 canvas.drawLine(countScale * mScaleMargin + finalX, mRectHeight,
     countScale * mScaleMargin + finalX, mRectHeight - mScaleMaxHeight - mScaleHeight, paint);
}

@Override
public boolean onTouchEvent(MotionEvent event) {
  int x = (int) event.getX();
  switch (event.getAction()) {
    case MotionEvent.ACTION_DOWN:
      if (mScroller != null && !mScroller.isFinished()) {
        mScroller.abortAnimation();
      }
      mScrollLastX = x;
      return true;
    case MotionEvent.ACTION_MOVE:
      int dataX = mScrollLastX - x;
      if (mCountScale - mTempScale < 0) { //向右边滑动
        if (mCountScale <= mMin && dataX <= 0) //禁止继续向右滑动
          return super.onTouchEvent(event);
      } else if (mCountScale - mTempScale > 0) { //向左边滑动
        if (mCountScale >= mMax && dataX >= 0) //禁止继续向左滑动
          return super.onTouchEvent(event);
      }
      smoothScrollBy(dataX, 0);
      mScrollLastX = x;
      postInvalidate();
      mTempScale = mCountScale;
      return true;
    case MotionEvent.ACTION_UP:
      if (mCountScale < mMin) mCountScale = mMin;
      if (mCountScale > mMax) mCountScale = mMax;
      int finalX = (mCountScale - mMidCountScale) * mScaleMargin;
      mScroller.setFinalX(finalX); //纠正指针位置
      postInvalidate();
      return true;
  }
  return super.onTouchEvent(event);
}