将 XAML 转换为 PDF 并为 Xamarin.Forms UWP 项目对其进行分页

问题描述

直到最近，在我不知何故退出 Dev Limbo 的项目中，我一直坚持如何实现将报告从 StackLayout“导出”到 PDF 的目标。

--背景故事--

以前，我尝试继续使用已放置（在项目中）PDFSharp 包将 XAML 中显示的数据转换为客户端的 PDF。长话短说，我无法让 PDFSharp 做我需要它做的事情，于是转向 Syncfusion。它们似乎具有实现这一目标所需的功能。根据他们拥有的代码示例，我能够接近我的目标，但还不够。它们有捕获部分和分页部分，但不是两者的组合。我基本上需要对 CaptureAsync() 保存的屏幕截图进行分页，以制作整个报告的 pdf。

解决方法

--这是如何解决的？--

在进行了一些挖掘之后，我在这个 article 中找到了一个答案（我永远感激）并使用它制定了一个解决方案。

这是我的 XAML 内容页面的上下文示例：

<?xml version="1.0" encoding="utf-8"?>
<ContentPage xmlns="http://xamarin.com/schemas/2014/forms"
             xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
             xmlns:controls="clr-namespace:ReportTool.Controls"
             x:Class="ReportTool.ReportViewer">
    <ContentPage.Content>
        <StackLayout Style="{StaticResource TopLevelStackLayout}">

            <!-- Body Block -->
            <Grid x:Name="MainGrid"  Style="{StaticResource MainContainingGrid}">
                <Grid.ColumnDefinitions>
                    <ColumnDefinition Width="1*" />
                </Grid.ColumnDefinitions>
                <Grid.RowDefinitions>
                    <RowDefinition Height="1*" />
                </Grid.RowDefinitions>
                <ScrollView x:Name="MainScrollLayout" VerticalOptions="Fill" HorizontalOptions="Fill" Grid.Row="0" Grid.Column="0" BackgroundColor="#FFFFFF" MinimumWidthRequest="700">
                    <StackLayout x:Name="MainStackLayout" Style="{StaticResource MainBkg}">
                        
                        <Button x:Name="DownloadPdfBtn"  Text="Export to PDF" Clicked="DownloadPdfBtn_OnClicked" TextColor="White" BackgroundColor="DodgerBlue" VerticalOptions="Start" HorizontalOptions="Start" />

                        <Image Source="~\..\Assets\Logos\CompanyLogo.png" Margin="0,60,10" HorizontalOptions="Center" />
                        <Label x:Name="TitlePageTitleText" Style="{StaticResource ReportViewerTitleTextMain}" Text="{StaticResource CompanyAnalysisReport}" />
                        <Label x:Name="TitlePagePreparedFor" Style="{StaticResource ReportViewerTitleTextMiddle}" Text="{StaticResource PreparedFor}" />
                        <Label x:Name="TitlePageOrganizationName" Style="{StaticResource ReportViewerTitleTextMiddle}" />
                        <Label x:Name="TitlePageOrganizationAddress1" Style="{StaticResource ReportViewerTitleTextMiddle}" />
                        <Label x:Name="TitlePageOrganizationAddress2" Style="{StaticResource ReportViewerTitleTextMiddle}" />
                        <Label x:Name="TitlePageOrganizationCityStateZip" Style="{StaticResource ReportViewerTitleTextLast}" />

                        <Grid x:Name="ReportGrid" Style="{StaticResource ReportGridBody}">
                            <Grid.ColumnDefinitions>
                                <ColumnDefinition Width="90"/>
                                <ColumnDefinition Width="1*"/>
                                <ColumnDefinition Width="125"/>
                                <ColumnDefinition Width="Auto"/>
                                <ColumnDefinition Width="Auto"/>
                                <ColumnDefinition Width="1*"/>
                            </Grid.ColumnDefinitions>
                            <Grid.RowDefinitions>
                                <RowDefinition Height="Auto"/>
                            </Grid.RowDefinitions>
                        </Grid>

                    </StackLayout>
                </ScrollView>
            </Grid>
        </StackLayout>
    </ContentPage.Content>
</ContentPage>

这是节目明星的代码，ExportToPdf 按钮：

using Syncfusion.Drawing;
using Syncfusion.Pdf;
using Syncfusion.Pdf.Graphics;

private async void DownloadPdfBtn_OnClicked(object sender,EventArgs e)
{
  try
  {
     var filename = "SurveyReport_" + ((App)Application.Current).CurrentUser.UserName + "_" + DateTime.UtcNow.ToString("MMddyy") + ".pdf";
                
     // Init Memory Stream.
     var stream = new MemoryStream();
                
     //Create a new PDF document
     using (var document = new PdfDocument())
     {
       // Add page to the PDF document.
       var page = document.Pages.Add();

      // Get the scroll view height.
      var xamlPageHeight = MainScrollLayout.ContentSize.Height;

      // Get the page dimensions.
      var pageWidth = page.GetClientSize().Width;
      var pageHeight = page.GetClientSize().Height;

      // Capture the number of pages.
      var numberOfPages = (int)Math.Ceiling(xamlPageHeight / pageHeight);
                    
      for (var i = 0; i < numberOfPages; i++)
      {
        // Find beginning of page.
        await MainScrollLayout.ScrollToAsync(0,i * pageHeight,false).ConfigureAwait(false);

        // Capture the XAML page as an image and returns the image in memory stream.
        var byteData = await DependencyService.Get<IExportPdf>().CaptureAsync();
        var imageStream = new MemoryStream(byteData);
                    
        // Load the image in PdfBitmap.
        var pdfBitmapImage = new PdfBitmap(imageStream);

        // Set the pdf page settings.
        document.PageSettings.Margins.All = 0;
        document.PageSettings.Orientation = PdfPageOrientation.Portrait;
        document.PageSettings.Size = new SizeF(pageWidth,pageHeight);
                        
        // Add new page for graphics (otherwise graphics won't know where to draw the rest of the image)
        page = document.Pages.Add();

        // Graphics for drawing image to pdf.
        var graphics = page.Graphics;

        // Draw the image to the page.
        graphics.DrawImage(pdfBitmapImage,pageWidth,pageHeight);

        // Insert page at i position.
        document.Pages.Insert(i,page);

        // Save the document into memory stream.
        document.Save(stream);
      }
     }
                    
     stream.Position = 0;

     // Save the stream as a file in the device and invoke it for viewing.
     await Xamarin.Forms.DependencyService.Get<IExportPdf>().Save(filename,"application/pdf",stream);
    }
    catch (Exception ex)
    {
        DisplayErrorAlert("DownloadPdfBtn_OnClicked",ex.StackTrace);
    }
}

需要注意的是，为了保存本地内存以外的任何地方，您需要一个依赖项。幸运的是，Syncfusion 提供了一个片段供您使用。为了您的时间，我将分享这些片段。您将需要添加两个 .cs 文件，一个具有捕获/保存功能的类文件和一个用于您的应用的接口文件。

捕获/保存类：

using System;
using System.Collections.Generic;
using System.IO;
using System.Linq;
using System.Runtime.InteropServices.WindowsRuntime;
using System.Threading.Tasks;
using Windows.Graphics.Display;
using Windows.Graphics.Imaging;
using Windows.Storage;
using Windows.Storage.Pickers;
using Windows.Storage.Streams;
using Windows.UI.Xaml;
using Windows.UI.Xaml.Media.Imaging;
using Xamarin.Forms;

public class ExportPdf : IExportPdf
{
    public async Task<byte[]> CaptureAsync()
    {
        var renderTargetBitmap = new RenderTargetBitmap();
        await renderTargetBitmap.RenderAsync(Window.Current.Content);
            
        var pixelBuffer = await renderTargetBitmap.GetPixelsAsync();
        var pixels = pixelBuffer.ToArray();
            
        var displayInformation = DisplayInformation.GetForCurrentView().LogicalDpi;
            
        var stream = new InMemoryRandomAccessStream();
            
        var encoder = await BitmapEncoder.CreateAsync(BitmapEncoder.JpegEncoderId,stream);
        encoder.SetPixelData(
            BitmapPixelFormat.Bgra8,BitmapAlphaMode.Ignore,(uint)renderTargetBitmap.PixelWidth,(uint)renderTargetBitmap.PixelHeight,displayInformation,pixels);
        await encoder.FlushAsync();
            
        stream.Seek(0);
        var readStream = stream.AsStreamForRead();
        var bytes = new byte[readStream.Length];
        await readStream.ReadAsync(bytes,bytes.Length);

        return bytes;
    }

    public async Task Save(string filename,string contentType,MemoryStream stream)
    {
        if (Device.Idiom != TargetIdiom.Desktop)
        {
            var local = ApplicationData.Current.LocalFolder;
            var outFile = await local.CreateFileAsync(filename,CreationCollisionOption.ReplaceExisting);
            using (var outStream = await outFile.OpenStreamForWriteAsync()) { await outStream.WriteAsync(stream.ToArray(),(int)stream.Length); }

            if (contentType != "application/html") await Windows.System.Launcher.LaunchFileAsync(outFile);
        }
        else
        {
            StorageFile storageFile = null;
            var savePicker = new FileSavePicker
            {
                SuggestedStartLocation = PickerLocationId.Desktop,SuggestedFileName = filename
            };
            switch (contentType)
            {
                case "application/vnd.openxmlformats-officedocument.presentationml.presentation":
                    savePicker.FileTypeChoices.Add("PowerPoint Presentation",new List<string> { ".pptx" });

                    break;

                case "application/msexcel":
                        savePicker.FileTypeChoices.Add("Excel Files",new List<string> { ".xlsx" });

                    break;

                case "application/msword":
                        savePicker.FileTypeChoices.Add("Word Document",new List<string> { ".docx" });

                    break;

                case "application/pdf":
                        savePicker.FileTypeChoices.Add("Adobe PDF Document",new List<string> { ".pdf" });

                    break;
                case "application/html":
                        savePicker.FileTypeChoices.Add("HTML Files",new List<string> { ".html" });

                    break;
            }

            storageFile = await savePicker.PickSaveFileAsync();

            using (var outStream = await storageFile.OpenStreamForWriteAsync())
            {
                await outStream.WriteAsync(stream.ToArray(),(int)stream.Length);
                await outStream.FlushAsync();
                outStream.Dispose();
            }

            stream.Flush();
            stream.Dispose();
            await Windows.System.Launcher.LaunchFileAsync(storageFile);
        }
    }
}

界面：

using System.IO;
using System.Threading.Tasks;

public interface IExportPdf
{
    Task Save(string filename,MemoryStream stream);
    Task<byte[]> CaptureAsync();
}

那应该可以！我希望这可以帮助任何承担过类似任务的人！