Xamarin 表单（android 项目）使用 Skia 图形库渲染图像时出错

Question

我正在尝试在我的 xamarin 表单解决方案中使用 skia 图形库加载和渲染图像。当我尝试渲染图像（运行 android 项目）时，出现以下错误：

Value cannot be null. Parameter name: codec

代码如下：

void OnPainting(object sender, SKPaintSurfaceEventArgs e)
{

    var surface = e.Surface;
    var canvas = surface.Canvas;

    canvas.Clear(SKColors.White);

    var filename = "test.jpg";

    using (var stream = new SKFileStream(filename))
    using (var bitmap = SKBitmap.Decode(stream)) // the error occurs on this line
    using (var paint = new SKPaint())  
    {
      canvas.DrawBitmap(bitmap, SKRect.Create(200, 200), paint);
    }
}

我在网上找不到任何 xamarin 的示例代码。任何示例代码或链接将不胜感激。

提前致谢

Answer 1

Value cannot be null. Parameter name: codec

我认为您可能在此处得到一个空对象：using (var stream = new SKFileStream(filename))。我试着创建了一个演示，它运行良好。

XAML:

<ContentPage xmlns="http://xamarin.com/schemas/2014/forms"
             xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
             xmlns:skiaviews="clr-namespace:SkiaSharp.Views.Forms;assembly=SkiaSharp.Views.Forms"
             x:Class="FormsIssue6.Page1">
    <Grid>
        <skiaviews:SKCanvasView x:Name="mycanvas" PaintSurface="OnPainting" />
    </Grid>
</ContentPage>

后面的代码：

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

    var assembly = typeof(Page1).GetTypeInfo().Assembly;
    var fileStream = assembly.GetManifestResourceStream("YOUR-FILE-FULL-NAME");
    // clear the canvas / fill with white
    canvas.DrawColor(SKColors.White);

    // decode the bitmap from the stream
    using (var stream = new SKManagedStream(fileStream))
    using (var bitmap = SKBitmap.Decode(stream))
    using (var paint = new SKPaint())
    {
        // create the image filter
        using (var filter = SKImageFilter.CreateBlur(5, 5))
        {
            paint.ImageFilter = filter;

            // draw the bitmap through the filter
            canvas.DrawBitmap(bitmap, SKRect.Create(640, 480), paint);
        }
    }
}

上面代码中的文件名应该是"YOUR PROJECT NAMESPACE"."File NAME"，这个文件放在PCL中，这个文件的build action必须是"Embedded Resource".有关使用文件的更多信息，您可以参考 Files.

I cannot find any sample code online for xamarin. Any sample code or links would be much appreciated.

Github上的包本身有Xamarin.Forms的代码示例，你可以参考FormsSample。

Xamarin 表单（android 项目）使用 Skia 图形库渲染图像时出错

Xamarin forms (android project) error rendering image using Skia graphics library

xamarin

xamarin.android

xamarin.forms

skia

skiasharp