[MAUI]用纯C#代码写两个漂亮的时钟

谷歌在2021年5月份推出的Android 12给我们带来了新的UI设计规范Material You，你是否已经体验到了Material You设计的魅力了呢？

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。

<Path Grid.Row="0"
        Grid.Column="1"
        Stroke="white"
        Fill="#FFEED9"
        IsVisible="true"
        x:Name="ModulatedPath">
    <Path.Data>
        <PathGeometry>
            <PathGeometry.Figures>
                <PathFigureCollection>
                    <PathFigure IsClosed="True" x:Name="MainPathFigure">
                        <PathFigure.Segments>
                            <PathSegmentCollection x:Name="MainPathSegmentCollection">

                            </PathSegmentCollection>
                        </PathFigure.Segments>
                    </PathFigure>

                </PathFigureCollection>
            </PathGeometry.Figures>
        </PathGeometry>
    </Path.Data>
</Path>

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<Point>();
    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 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)0.8, 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);
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();
    }
}

配置一个定时器，每秒刷新各指针位置

IDispatcherTimer _timer;

public Clock1()
{
   
    ...
    this.SizeChanged+=ContentView_SizeChanged;
    _timer=  Dispatcher.CreateTimer();
    _timer.Interval=TimeSpan.FromSeconds(1);
    _timer.Tick+=_timer_Tick;
    _timer.Start();
}

private void _timer_Tick(object sender, EventArgs e)
{
    this.canvasView?.InvalidateSurface();
}

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");

});

绘制表盘

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：

<Grid>

    <Ellipse Grid.Row="0"
                Grid.Column="1"
                Stroke="white"
                Fill="#FFEED9"
                IsVisible="true"
                HeightRequest="200"
                WidthRequest="200"
                x:Name="ModulatedPath">
    </Ellipse>
    <Grid TranslationY="-15">
        <Grid.RowDefinitions>
            <RowDefinition></RowDefinition>
            <RowDefinition></RowDefinition>
        </Grid.RowDefinitions>
        <Grid.ColumnDefinitions>
            <ColumnDefinition></ColumnDefinition>
            <ColumnDefinition></ColumnDefinition>
        </Grid.ColumnDefinitions>
        <Label   Grid.Row="0"
                    Grid.ColumnSpan="2"
                    Text="12"
                    Style="{StaticResource ClockPlateNumberLabelStyle}"></Label>

        <Label   Grid.RowSpan="2"
                    Grid.Column="1"
                    Text="3"
                    Style="{StaticResource ClockPlateNumberLabelStyle}"></Label>

        <Label   Grid.Row="1"
                    Grid.ColumnSpan="2"
                    Text="6"
                    Style="{StaticResource ClockPlateNumberLabelStyle}"></Label>

        <Label   Grid.RowSpan="2"
                    Grid.Column="0"
                    Text="9"
                    Style="{StaticResource ClockPlateNumberLabelStyle}"></Label>

    </Grid>



    <forms:SKCanvasView x:Name="canvasView"
                        PaintSurface="OnCanvasViewPaintSurface" />

    <Label FontSize="28"
            HorizontalOptions="Center"
            VerticalOptions="Center"
            x:Name="labelView"></Label>
</Grid>

同样我们需要放置SKCanvasView对象用于绘制指针

其中ClockPlateNumberLabelStyle定义如下：

<Style TargetType="Label"
        x:Key="ClockPlateNumberLabelStyle">
    <Setter Property="HorizontalTextAlignment"
            Value="Center"></Setter>
    <Setter Property="VerticalTextAlignment"
            Value="Center"></Setter>
    <Setter Property="VerticalOptions"
            Value="Center"></Setter>
    <Setter Property="FontAttributes"
            Value="Bold"></Setter>
    <Setter Property="FontSize"
            Value="120"></Setter>
    <Setter Property="TextColor"
            Value="#F9BC49"></Setter>
    <Setter Property="FontFamily"
            Value="URWGeometricBlack"></Setter>
</Style>

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