本文只是运用一些自定义View的基础知识，大家如果没有兴趣跟着步骤一步一步来
如果你想对这部分知识进行下复习和梳理，也可以跟着步骤来看下，文中内容若有疏漏，还望不吝赐教。

效果图

分析

自定义View最主要的是梳理清楚绘制的逻辑。弄明白逻辑了，一步一步来，复杂的View也就没有那么复杂了。

绘制步骤整理如下：

绘制一个发光的弧形
绘制刻度和数字
绘制指针阴影
绘制中间黑色圆形背景
绘制表针
绘制深蓝色发光圆形
绘制表盘文字
添加底部控件

实现

View 需要用到发光的效果，我们采用 shader 来实现，那么我们需要首先关闭硬件加速。

  // 关闭硬件加速
  setLayerType(LAYER_TYPE_SOFTWARE, null);

1. 绘制一个发光的弧形

  canvas.translate(getPaddingLeft() + radiusDial, getPaddingTop() + radiusDia
  arcPaint.setShader(null);
  arcPaint.setStyle(Paint.Style.STROKE);
  arcPaint.setAntiAlias(true);
  arcPaint.setAlpha(70);
  arcPaint.setStyle(Paint.Style.STROKE);
  arcPaint.setStrokeWidth(strokeWidthDial);
  arcPaint.setShadowLayer(10, 0, 0, Color.parseColor("#FFFFFF"));
  arcPaint.setColor(Color.parseColor("#38F9FD"));
  canvas.drawArc(mRect, 150, (360 - openAngle), false, arcPaint);

2. 绘制刻度和数字

  canvas.rotate(150);
  for (int i = 0; i < clockPointNum + 1; i++) {
      pointerPaint.setColor(colorDialMiddle);
      if (i % 10 == 0) {     //长表针
          pointerPaint.setStrokeWidth(3);
          canvas.drawLine(radiusDial - DEFAULT_border - strokeWidthDial, 0, radiusDial - strokeWidthDial - dp2px(15), 0, pointerPaint);
          drawPointerText(canvas, i);
      } else if (i % 5 == 0f) {    //短表针
          pointerPaint.setStrokeWidth(2);
          canvas.drawLine(radiusDial - DEFAULT_border - strokeWidthDial, 0, radiusDial - strokeWidthDial - dp2px(9), 0, pointerPaint);
      }
      canvas.rotate((360 - openAngle) / clockPointNum);
  }
  canvas.rotate(-((180 - openAngle) / 2 + ((360 - openAngle) / clockPointNum)));

  /**
   * 绘制刻度数字
   */
    private void drawPointerText(Canvas canvas, int i) {
        canvas.save();
        pointerPaint.setColor(getResources().getColor(R.color.white));
        int currentCenterX = (int) (radiusDial - strokeWidthDial - dp2px(21) - pointerPaint.measureText(String.valueOf(i)) / 2);
        canvas.translate(currentCenterX, 0);
        canvas.rotate(360 - 150 - ((360 - openAngle) / clockPointNum) * i);        //坐标系总旋转角度为360度
        int textBaseLine = (int) (0 + (fontMetrics.bottom - fontMetrics.top) / 2 - fontMetrics.bottom);
        canvas.drawText(String.valueOf(i + clockMinValue), 0, textBaseLine, pointerPaint);
    }

3. 绘制指针阴影

  int currentDegree = (int) ((currentValue - clockMinValue) * ((360 - openAngle) / clockPointNum) + 150);
  canvas.rotate(currentDegree);
  int[] colorSweep = {0xAAFFE9EC, 0x0028E9EC, 0xAA28E9EC};
  float[] position = {0f, 0.9f, 1f};
  SweepGradient mShader = new SweepGradient(0, 0, colorSweep, position);
  arcPaint.setShader(mShader);
  arcPaint.setStyle(Paint.Style.STROKE);
  arcPaint.setStrokeWidth((float) (radiusDial * 0.4));
  arcPaint.clearShadowLayer();
  RectF mRect = new RectF((float) (-mRealRadius - DEFAULT_border + radiusDial * 0.2), (float) (-mRealRadius - 
  DEFAULT_border + radiusDial * 0.2),
          (float) (mRealRadius + DEFAULT_border - radiusDial * 0.2), (float) (mRealRadius + DEFAULT_border - radiusDial * 0.2));
  canvas.drawArc(mRect, 360 - (currentDegree - 150), (currentDegree - 150), false, arcPaint);

4. 绘制中间黑色圆形背景

  canvas.restore();
  canvas.translate(getPaddingLeft() + radiusDial, getPaddingTop() + radiusDial);
  Paint pointerPaint = new Paint();
  pointerPaint.setAntiAlias(true);
  pointerPaint.setStyle(Paint.Style.FILL);
  pointerPaint.setColor(Color.parseColor("#05002D"));
  canvas.drawCircle(0, 0, (float) (radiusDial * 0.6), pointerPaint);

5. 绘制表针

  canvas.save();
  int currentDegree = (int) ((currentValue - clockMinValue) * ((360 - openAngle) / clockPointNum) + 150);
  canvas.rotate(currentDegree);
  titlePaint.setColor(Color.WHITE);
  titlePaint.setAntiAlias(true);
  pointerPath.moveTo(radiusDial - dp2px(12), 0);
  pointerPath.lineTo(0, -dp2px(5));
  pointerPath.lineTo(-12, 0);
  pointerPath.lineTo(0, dp2px(5));
  pointerPath.close();
  canvas.drawPath(pointerPath, titlePaint);
  canvas.save();
  canvas.restore();

6. 绘制深蓝色发光圆形

  canvas.rotate(0);
  canvas.restore();
  Paint pointerPaint = new Paint();
  pointerPaint.setAntiAlias(true);
  pointerPaint.setStyle(Paint.Style.FILL);
  pointerPaint.setColor(Color.parseColor("#050D3D"));
  pointerPaint.setShadowLayer(15, 0, 0, Color.parseColor("#006EC6"));
  canvas.drawCircle(0, 0, (float) (radiusDial * 0.4), pointerPaint);

7. 绘制表盘文字

  titlePaint.setColor(Color.WHITE);
  titlePaint.setColor(titleDialColor);
  titlePaint.setTextSize(titleDialSize);
  canvas.drawText(formatData(currentValue), 0, 0, titlePaint);
  titlePaint.setColor(Color.parseColor("#38F9FD"));
  titlePaint.setTextSize(sp2px(14));
  canvas.drawText("(" + dataUnit + ")", 0, dp2px(18), titlePaint);

8. 添加底部控件

这部分代码就比较灵活了，仪表盘主体绘制出来以后，可以在布局文件中增加其它底部控件。并设置相应点击事件等。在此略过不表

#最后
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