我尝试通过.NET MAUI Blazor混合项目打印文档。当我在做的时候，我看到了与android os互操作的地方在platform/android文件夹根目录中。下面是我在开发打印代码时遵循的文档，

1. Printing Photos in android Print manager
2. Printing Custom Document in android
   在android中打印照片是成功的，但现在我想打印自定义文档，因为我想打印PDF。下面是成功的图像打印和不成功的PDF打印的代码。PDF和图像都可以转换为base64字符串。
   下面是.NET中接口代码

namespace PrintMAUI.Services
{
    public interface IPrintCalller
    {
        Task<bool> printImage(byte[] bitmapBytes);
        Task<bool> printPDF(byte[] pdfBytes);
    }
}

为Android平台创建的类

namespace PrintMAUI.Platforms
{
    public class PrintCaller : MauiAppCompatActivity, IPrintCalller
    {
        public async Task<bool> printImage(byte[] bitmapBytes)
        {
            try
            {
                //Microsoft.Maui.ApplicationModel.Platform.CurrentActivity.Context
               
                PrintHelper photoPrinter = new PrintHelper(Platform.CurrentActivity);
                photoPrinter.ScaleMode = PrintHelper.ScaleModeFill;
                Bitmap bitmap = await BitmapFactory.DecodeByteArrayAsync(bitmapBytes, 0, bitmapBytes.Length);
                photoPrinter.PrintBitmap("Testing Print for BL", bitmap);
                return true;
            }catch (Exception ex)
            {
                return false;
            }
        }
        public async Task<bool> printPDF(byte[] pdfBytes)
        {
            try
            {
                
                PrintManager printManager = Platform.CurrentActivity.GetSystemService(Android.Content.Context.PrintService).JavaCast<PrintManager>();
                string jobName = "simple Print Job";
                printManager.Print(jobName, new CustomPrintDocumentAdapter(pdfBytes), null);
                return true;
            }catch(Exception ex)
            {
                return false;
            }
        }
    }
}

自定义打印适配器

using Android.Graphics.Pdf;
using Android.OS;
using Android.Print;
using Android.Print.Pdf;
using Android.Runtime;
using Java.IO;
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using static Android.Print.PrintAttributes;
namespace PrintMAUI.Platforms
{
    public class CustomPrintDocumentAdapter : PrintDocumentAdapter
    {
        //private byte[] data;
        private int totalPages = 0;
        PrintedPdfDocument pdfDocument;
        public CustomPrintDocumentAdapter(byte[] data)
        {
            //this.data = data;
        }
        public override void OnLayout(PrintAttributes oldAttributes, PrintAttributes newAttributes, CancellationSignal cancellationSignal, LayoutResultCallback callback, Bundle extras)
        {
            pdfDocument = new PrintedPdfDocument(Platform.CurrentActivity,newAttributes);
            if (cancellationSignal.IsCanceled)
            {
                callback.OnLayoutCancelled();
                return;
            }
            int pages = computePageCount(newAttributes);
            if(pages > 0)
            {
                PrintDocumentInfo pdi = new PrintDocumentInfo.Builder("PDF.pdf")
                    .SetContentType(Android.Print.PrintContentType.Document)
                    .SetPageCount(pages)
                    .Build();
                callback.OnLayoutFinished(pdi, true);
            }
            else
            {
                callback.OnLayoutFailed("Calculations Failed!");
            }
        }
        private bool containsPage(PageRange[] pages,int num)
        {
            //TODO: you have to do it
            return true;
        }
        public override void OnWrite(PageRange[] pages, ParcelFileDescriptor destination, CancellationSignal cancellationSignal, WriteResultCallback callback)
        {
            for (int i = 0; i < totalPages; i++)
            {
                // Check to see if this page is in the output range.
                if (containsPage(pages, i))
                {
                    // If so, add it to writtenPagesArray. writtenPagesArray.size()
                    // is used to compute the next output page index.
                    //writtenPagesArray.append(writtenPagesArray.size(), i);
                    PdfDocument.Page page = pdfDocument.StartPage(i);
                    // check for cancellation
                    if (cancellationSignal.IsCanceled)
                    {
                        callback.OnWriteCancelled();
                        pdfDocument.Close();
                        pdfDocument = null;
                        return;
                    }
                    // Rendering is complete, so page can be finalized.
                    pdfDocument.FinishPage(page);
                }
            }
            // Write PDF document to file
            try
            {
                //FileOutputStream stream = new FileOutputStream(destination.FileDescriptor);
                FileStream stream = new FileStream((string)destination.FileDescriptor, FileMode.Create, FileAccess.Write);
                pdfDocument.WriteTo(stream);
            }
            catch (Exception e)
            {
                callback.OnWriteFailed(e.ToString());
                return;
            }
            finally
            {
                pdfDocument.Close();
                pdfDocument = null;
            }
            //PageRange[] writtenPages = computeWrittenPages();
           /// Signal the print framework the document is complete
            callback.OnWriteFinished(pages);
        }
        private int computePageCount(PrintAttributes printAttributes)
        {
            int itemsPerPage = 4;
            MediaSize pageSize = printAttributes.GetMediaSize();
            if (!pageSize.IsPortrait)
            {
                itemsPerPage = 6;
            }
            int printItemCount = 1;
            return (int)Math.Ceiling((double)printItemCount/itemsPerPage);
        }
    }
}

我做了什么

1.首先，我尝试使用打印机SDK创建单独的项目，并从MAUI应用程序调用它。但由于政策限制，它没有成功。
1.然后我尝试将打印机SDK添加到MAUI项目中。它不工作
1.然后我试着用这种方法。我试着用android打印管理器打印文档。打印图像时成功。但我想从它的字节数组打印PDF。

我的期待

customprintdocumentadapter类中的这些行出现了无法修复的问题。无论如何我都有选角问题

FileStream stream = new FileStream((string)destination.FileDescriptor, FileMode.Create, FileAccess.Write);
                pdfDocument.WriteTo(stream);

我想知道怎么补救？
第二件事是我认为这段代码可能有一些必须理解的蓬茨如何customprintdocumentadapter支持打印自定义文档。有人能解释一下吗
google文档有这个代码

writtenPagesArray.append(writtenPagesArray.size(), i);

但我找不到它从哪里来。