[MAUI]用纯C#代码写两个漂亮的时钟

Posted on by hackdl

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目录
  • 时钟1

    • 绘制锯齿表盘
    • 绘制指针
    • 绘制沿路径文本
  • 时钟2

    • 绘制表盘
    • 绘制指针
    • 项目地址

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。

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

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：

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

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