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);
</pre>
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
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