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(资料图片)
在原生主屏幕启动器中，有一个时钟小部件。这个小部件可以选择表盘风格。
图：Android 12的时钟小部件
今天挑战在.NET MAU中实现这个Material You风格时钟。
最终效果如下：
时钟1绘制锯齿表盘锯齿表盘是正玄波曲线闭合成一个圆形。创建Clock1，打开Xaml文件
在页面布局中创建一个Path对象，设置Stroke和Fill属性。
在codebehind中，订阅SizeChanged事件，当控件大小发生变化时，重新绘制表盘。
public Clock1(){ InitializeComponent(); this.SizeChanged+=ContentView_SizeChanged;}正弦曲线绘制原理
单位圆中的正弦函数在平面直角坐标系中可以映射为一个波形曲线，下图所示在0-2π范围中y=sin(x)的图像。
其中最低点和最高点决定了波形的振幅，他们与平衡点的距离即单位圆的半径
设置变量 r为平衡点，r2为最高点，r3为最低点。
centerX和centerY为圆心坐标。segemts为绘制的线段数，越大锯齿越密集。
private void ContentView_SizeChanged(object sender, EventArgs e){ var length = (float)Math.Min(this.Width, this.Height) * 0.95; var centerX = (float)this.Width / 2; var centerY = (float)this.Height / 2; var points = new List(); var r = length / 2; var r2 = r * 1.1; var r3 = r * 0.9; var index = 0; var segments = 40; 首先计算各平衡点在圆周上的离散分布坐标（x,y）
根据index的奇偶性，给与当前点最高点或最低点的半径。
根据各分配的半径计算调整后的离散点坐标
代码如下：
...for (var i = 0; i < segments; i += 2){ var x = r * Math.Cos(i * 2 * Math.PI / segments) + centerX; var y = r * Math.Sin(i * 2 * Math.PI / segments) + centerY; points.Add(new Point((float)x, (float)y)); var currentR = index++ % 2 == 0 ? r2 : r3; x = currentR * Math.Cos((i + 1) * 2 * Math.PI / segments) + centerX; y = currentR * Math.Sin((i + 1) * 2 * Math.PI / segments) + centerY; points.Add(new Point((float)x, (float)y));}如此，我们得到一个闭合的锯齿圆形表盘
绘制指针在表盘上绘制时钟指针，需要计算时针、分针、秒针的角度，然后根据角度旋转画布，绘制指针。
秒针每秒钟转动6度，
分针每分钟转动6度，并叠加每秒0.1度。
时针每小时转动30度。并叠加每分钟0.5度。
其中时针和分针由宽度为15的实心填充圆角线条构成
DateTime dateTime = DateTime.Now;// Hour handstrokePaint.Color = SKColor.Parse("#5E4000");strokePaint.StrokeWidth = 15;canvas.Save();canvas.RotateDegrees(30 * dateTime.Hour + dateTime.Minute / 2f);canvas.DrawLine(0, 0, 0, -r*(float)0.4, strokePaint);canvas.Restore();// Minute handstrokePaint.Color = SKColor.Parse("#9C6D00");canvas.Save();canvas.RotateDegrees(6 * dateTime.Minute + dateTime.Second / 10f);canvas.DrawLine(0, 0, 0, -r*(float)0.8, strokePaint);canvas.Restore();// Second handstrokePaint.Color = SKColor.Parse("#657E3F");canvas.Save();canvas.RotateDegrees(6 * dateTime.Second);strokePaint.StrokeWidth *=(float)0.5;strokePaint.Style=SKPaintStyle.Fill;canvas.DrawCircle(0, -r*(float)0.8, strokePaint.StrokeWidth, strokePaint);canvas.Restore();指针效果如下：
其中秒针需要绘制一个点，在其以圆心为中心的对侧绘制一个带有日期的文本
绘制沿路径文本首先绘制文本路径，它是一个圆弧，在初始状态圆弧的角度为20度，圆弧的起始角度为70度，终止角度为110度。
var pathAngle = 20;var startAngle = 90-pathAngle;var sweepAngle = pathAngle*2;var rect = new SKRect(-r*(float)0.8, -r*(float)0.8, r*(float)0.8, r*(float)0.8);使用SkiaSharp的DrawTextOnPath方法绘制沿路径的文本，详情请查看官方文档
using (SKPath path = new SKPath()){ path.AddArc(rect, startAngle, sweepAngle); canvas.DrawTextOnPath(dateStr, path, new SKPoint(), strokePaint);}指针效果如下：
时钟1的完整代码如下：
void OnCanvasViewPaintSurface(object sender, SKPaintSurfaceEventArgs args){ SKImageInfo info = args.Info; SKSurface surface = args.Surface; SKCanvas canvas = surface.Canvas; canvas.Clear(); using (SKPaint strokePaint = new SKPaint()) using (SKPaint fillPaint = new SKPaint()) { strokePaint.Style = SKPaintStyle.Stroke; strokePaint.StrokeCap = SKStrokeCap.Round; fillPaint.Style = SKPaintStyle.Fill; fillPaint.Color = SKColors.Transparent; // Transform for 100-radius circle centered at origin var r = 100f; canvas.Translate(info.Width / 2f, info.Height / 2f); canvas.Scale(Math.Min(info.Width / 200f, info.Height / 200f)); DateTime dateTime = DateTime.Now; // Hour hand strokePaint.Color = SKColor.Parse("#5E4000"); strokePaint.StrokeWidth = 15; canvas.Save(); canvas.RotateDegrees(30 * dateTime.Hour + dateTime.Minute / 2f); canvas.DrawLine(0, 0, 0, -r*(float)0.4, strokePaint); canvas.Restore(); // Minute hand strokePaint.Color = SKColor.Parse("#9C6D00"); canvas.Save(); canvas.RotateDegrees(6 * dateTime.Minute + dateTime.Second / 10f); canvas.DrawLine(0, 0, 0, -r*(float)0.62, strokePaint); canvas.Restore(); // Second hand strokePaint.Color = SKColor.Parse("#657E3F"); canvas.Save(); canvas.RotateDegrees(6 * dateTime.Second); strokePaint.StrokeWidth *=(float)0.5; strokePaint.Style=SKPaintStyle.Fill; canvas.DrawCircle(0, -r*(float)0.8, strokePaint.StrokeWidth, strokePaint); strokePaint.Color = SKColors.Black; strokePaint.StrokeWidth = 1; var dateStr = dateTime.ToString("M"); var pathAngle = 20; var startAngle = 90-pathAngle; var sweepAngle = pathAngle*2; var rect = new SKRect(-r*(float)0.8, -r*(float)0.8, r*(float)0.8, r*(float)0.8); using (SKPath path = new SKPath()) { path.AddArc(rect, startAngle, sweepAngle); //canvas.DrawPath(path, strokePaint); canvas.DrawTextOnPath(dateStr, path, new SKPoint(), strokePaint); } canvas.Restore(); }}时钟1 效果如下：
时钟2将URWGeometricBlack字体文件放到Fonts目录下
在MauiProgram.cs中注册字体
.ConfigureFonts(fonts =>{ ... fonts.AddFont("URWGeometricBlack.otf", "URWGeometricBlack");});时钟2的表盘相对简单，是一个简单的圆配简洁抽象的数字刻度组成创建Clock2，打开Xaml文件，代码如下：
同样我们需要放置SKCanvasView对象用于绘制指针
其中ClockPlateNumberLabelStyle定义如下：
效果如下：
绘制指针时钟2的指针绘制原理与时钟1类似，此处将不赘述，完整代码如下：
void OnCanvasViewPaintSurface(object sender, SKPaintSurfaceEventArgs args){ SKImageInfo info = args.Info; SKSurface surface = args.Surface; SKCanvas canvas = surface.Canvas; canvas.Clear(); using (SKPaint strokePaint = new SKPaint()) using (SKPaint fillPaint = new SKPaint()) { strokePaint.Style = SKPaintStyle.Stroke; strokePaint.StrokeCap = SKStrokeCap.Round; fillPaint.Style = SKPaintStyle.Fill; fillPaint.Color = SKColors.Transparent; // Transform for 100-radius circle centered at origin var r = 100f; canvas.Translate(info.Width / 2f, info.Height / 2f); canvas.Scale(Math.Min(info.Width / 200f, info.Height / 200f)); DateTime dateTime = DateTime.Now; // Hour hand strokePaint.Color = SKColor.Parse("#5E4000"); strokePaint.StrokeWidth = 15; canvas.Save(); canvas.RotateDegrees(30 * dateTime.Hour + dateTime.Minute / 2f); canvas.DrawLine(0, 0, 0, -r*(float)0.4, strokePaint); canvas.Restore(); // Minute hand strokePaint.Color = SKColor.Parse("#9C6D00"); strokePaint.StrokeWidth = 5; canvas.Save(); canvas.RotateDegrees(6 * dateTime.Minute + dateTime.Second / 10f); canvas.DrawLine(0, 0, 0, -r*(float)0.8, strokePaint); canvas.Restore(); // Second hand strokePaint.Color = SKColor.Parse("#657E3F"); strokePaint.StrokeWidth = 2; canvas.Save(); canvas.RotateDegrees(6 * dateTime.Second); canvas.DrawLine(0, r*(float)0.1, 0, -r*(float)0.8, strokePaint); strokePaint.Style=SKPaintStyle.Fill; canvas.DrawCircle(0, 0, 5, strokePaint); canvas.Restore(); }}时钟2 效果如下
项目地址Github:maui-samples
关键词：
