如何在Maui Blazor特定平台跳过System.Drawing.Common依赖？

要解决MAUI Blazor中System.Drawing.Common跨平台依赖冲突的问题，核心思路是让非Windows平台完全不加载相关依赖包，同时通过平台专属实现拆分功能逻辑：

1. 条件引用依赖包 #

直接在项目文件（.csproj）中配置，仅让Windows平台引入Ghostscript和System.Drawing.Common，从根源避免iOS/Android打包时包含不兼容依赖：

<ItemGroup Condition="'$(TargetFramework)' == 'net8.0-windows10.0.19041.0'">
  <PackageReference Include="System.Drawing.Common" Version="8.0.0" />
  <PackageReference Include="Ghostscript.NET" Version="1.2.2" />
</ItemGroup>

2. 封装平台专属的PDF缩略图提取服务 #

先定义统一接口，隔离平台差异：

public interface IPdfThumbnailExtractor
{
    Task<byte[]?> ExtractThumbnailAsync(Stream pdfStream, int pageNumber = 0);
}

Windows平台实现（基于Ghostscript） #

用条件编译限定仅Windows编译这段代码：

#if WINDOWS
using Ghostscript.NET.Rasterizer;
using System.Drawing.Imaging;

namespace YourApp.Services
{
    public class WindowsPdfThumbnailExtractor : IPdfThumbnailExtractor
    {
        public async Task<byte[]?> ExtractThumbnailAsync(Stream pdfStream, int pageNumber = 0)
        {
            using var rasterizer = new GhostscriptRasterizer();
            rasterizer.Open(pdfStream);
            // Ghostscript页码从1开始，生成100x100的缩略图
            using var image = rasterizer.GetPage(100, 100, pageNumber + 1);
            using var ms = new MemoryStream();
            image.Save(ms, ImageFormat.Png);
            return ms.ToArray();
        }
    }
}
#endif

iOS/Android平台实现（基于跨平台替代库） #

用SkiaSharp实现跨平台PDF缩略图提取（需先引用对应平台的SkiaSharp原生包）：

#if ANDROID || IOS
using SkiaSharp;

namespace YourApp.Services
{
    public class MobilePdfThumbnailExtractor : IPdfThumbnailExtractor
    {
        public async Task<byte[]?> ExtractThumbnailAsync(Stream pdfStream, int pageNumber = 0)
        {
            try
            {
                using var pdf = SKDocument.Open(pdfStream);
                using var page = pdf.GetPage(pageNumber);
                // 按宽度缩放到100px，保持比例
                var scale = 100f / page.Size.Width;
                using var bitmap = SKBitmap.FromImage(page.ToImage((int)(page.Size.Width * scale), (int)(page.Size.Height * scale)));
                using var ms = new MemoryStream();
                bitmap.Encode(ms, SKEncodedImageFormat.Png, 100);
                return ms.ToArray();
            }
            catch
            {
                return null;
            }
        }
    }
}
#endif

对应的SkiaSharp包条件引用：

<ItemGroup Condition="'$(TargetFramework)' == 'net8.0-android'">
    <PackageReference Include="SkiaSharp.NativeAssets.Android" Version="2.88.6" />
</ItemGroup>
<ItemGroup Condition="'$(TargetFramework)' == 'net8.0-ios'">
    <PackageReference Include="SkiaSharp.NativeAssets.iOS" Version="2.88.6" />
</ItemGroup>
<ItemGroup>
    <PackageReference Include="SkiaSharp" Version="2.88.6" />
</ItemGroup>

3. 注册平台专属服务 #

在MauiProgram.cs中根据当前平台注入对应实现：

builder.Services.AddTransient<IPdfThumbnailExtractor>(sp =>
{
    if (DeviceInfo.Platform == DevicePlatform.WinUI)
    {
#if WINDOWS
        return new WindowsPdfThumbnailExtractor();
#endif
    }
#if ANDROID || IOS
    return new MobilePdfThumbnailExtractor();
#endif
    throw new NotSupportedException("当前平台不支持PDF缩略图提取");
});

4. Blazor组件中调用服务 #

注入服务后直接调用，无需额外判断平台（服务内部已处理）：

@inject IPdfThumbnailExtractor ThumbnailExtractor
@inject IJSRuntime JSRuntime

<input type="file" accept=".pdf" @onchange="HandleFileUpload" />
@if (thumbnailData != null)
{
    <img src="data:image/png;base64,@Convert.ToBase64String(thumbnailData)" alt="PDF缩略图" />
}

@code {
    private byte[]? thumbnailData;

    private async Task HandleFileUpload(InputFileChangeEventArgs e)
    {
        using var stream = e.File.OpenReadStream();
        thumbnailData = await ThumbnailExtractor.ExtractThumbnailAsync(stream);
        if (thumbnailData == null)
        {
            await JSRuntime.InvokeVoidAsync("alert", "无法提取PDF缩略图");
        }
        StateHasChanged();
    }
}

内容的提问来源于stack exchange，提问作者Matias Masso