Path 的move可以多次反复使用

1. // 绘制箭头
   
2. Path rollArrow = new Path();
   
3. rollArrow.moveTo(center.x - 3, (int)innerBoundingBox.top + 14);
   
4. rollArrow.lineTo(center.x, (int)innerBoundingBox.top + 10);
   
5. rollArrow.moveTo(center.x + 3, innerBoundingBox.top + 14);
   
6. rollArrow.lineTo(center.x, innerBoundingBox.top + 10);
   
7. canvas.drawPath(rollArrow, markerPaint);
   
8. // 绘制字符串
   
9. String rollText = String.valueOf(rollDegree);
   
10. double rollTextWidth = textPaint.measureText(rollText);
    
11. canvas.drawText(rollText, (float)(center.x - rollTextWidth / 2), innerBoundingBox.top + textHeight + 2, textPaint);