SkiaSharp跨平台绘图研究2Xamarin.Forms移动应用

SkiaSharp跨平台绘图研究2-Xamarin.Forms移动应用

继续之前的SkiaSharpDemo解决方案。

微软官网有Xamarin.Forms采用SkiaSharp绘图的详细介绍。

https://docs.microsoft.com/zh-cn/xamarin/xamarin-forms/user-interface/graphics/skiasharp/

创建Xamarin.Forms项目

项目名称XamarinDemo，只选择了安卓平台，空白初始屏幕，简单一点。

给XamarinDemo项目NuGet安装SkiaSharp.Views.Forms 2.80.3

在MainPage.xaml上添加一个SKCanvasView容器，存放画布，页面xaml代码非常相似。

<StackLayout>
        <Button x:Name="btnRefresh" Text="绘图" Margin="4"></Button>
        <skia:SKCanvasView x:Name="skContainer" HeightRequest="300" Margin="4">
        </skia:SKCanvasView>

    </StackLayout>

MainPage.xaml.cs的绘图代码，跟WPF项目几乎一样。

public partial class MainPage : ContentPage
    {
        public MainPage()
        {
            InitializeComponent();

            btnRefresh.Clicked += BtnRefresh_Clicked;
            skContainer.PaintSurface += SkContainer_PaintSurface;
        }

        private void BtnRefresh_Clicked(object sender, EventArgs e)
        {
            Debug.WriteLine($"{DateTimeOffset.Now}, 刷新画布");

            //强制画布重绘
            skContainer.InvalidateSurface();
        }

        private void SkContainer_PaintSurface(object sender, SkiaSharp.Views.Forms.SKPaintSurfaceEventArgs e)
        {
            var canvas = e.Surface.Canvas;

            canvas.Clear(SKColors.SkyBlue);

            var paint = new SKPaint
            {
                Color = SKColors.Black,
                IsAntialias = true,
                Typeface = SkiaChinaFont.ChinaFont,
                TextSize = 48
            };

            string msg = $"{DateTimeOffset.Now:T}, 还有1万行Skia绘图代码...";
            canvas.DrawText(msg, 0, 60, paint);

            var linePaint = new SKPaint()
            {
                Color = (DateTimeOffset.Now.Second % 4 <= 1) ? SKColors.Red : SKColors.Green,
                Style = SKPaintStyle.Stroke,//不填充
                StrokeWidth = 3,
            };
            canvas.DrawRect(10, 90, e.Info.Width - 20, e.Info.Height - 150, linePaint);

            msg += $", linePaint.Color={linePaint.Color}, skContainer.CanvasSize={skContainer.CanvasSize}";
            Debug.WriteLine(msg);
        }
    }

加载中文字库

安卓项目不太方便复制字体文件去APP目录，把DroidSansFallback.ttf设置为嵌入的资源，按照资源文件的方式去加载。

 /// <summary>
    /// Skia中文字体
    /// </summary>
    public static class SkiaChinaFont
    {
        public static SKTypeface ChinaFont { get; private set; }

        static SkiaChinaFont()
        {
            //加载资源方案，设置字体文件属性为嵌入的资源
            var fontStream = Assembly.GetExecutingAssembly().GetManifestResourceStream("XamarinDemo.DroidSansFallback.ttf");
            ChinaFont = SKTypeface.FromStream(fontStream);
        }
    }

运行测试

在VS2022自带的安卓模拟器上跑起来，绘图出来了，可以更新。

DEMO源代码参见：https://gitee.com/woodsun