How to: Retain the Image URI in an HTML Document

• Jun 10, 2019
• 4 minutes to read

This example provides more details on HTML export and describes how to store the original image URI in the exported document.

When RichEditControl loads an HTML document, it imports the document and converts it into a native document model, and then converts the native document to the resulting document’s format when it is saved.

The list below describes the two options to images on export to HTML.

• Embed images into the resulting file as base64-encoded data.

  HTML

  <img src="data:image/png;base64,,iVBORw0KGgoAAAANSUhEUgAAAQQAAA<!-- base64 data -->" width="260" height="90" alt="" style="border-width:0px;" />
  

• Save images as separate files.
  The images are named using the “image” word followed by its sequential number in a file. Images are saved to the folder with a name that combines the file name, an underscore and the “files” word. For example, the first png image in the resulting Test.html file is saved to Test_files\image0.png.

  HTML

  <img src="test_files/image0.png" alt="" style="border-width:0px;" />
  

Implement a Custom URI Provider

The HTML exporter uses a URI provider instance to obtain each image’s URI string. There are two built-in URI providers - the FileBasedUriProvider which provides image file names, and the DataStringUriProvider that constructs a tag for embedded base64 data. The built-in URI provider service (a service that implements the IUriProviderService interface) is used to obtain a provider instance.

You can implement a custom URI provider to specify a custom location for each image when the document is saved to HTML format. To accomplish this, create an IUriProvider descendant and register it in RichEditControl services.

Tip

The SubDocument.GetHtmlText method allows you to specify a custom URI provider as the method’s parameter, bypassing the URI provider service and the RichEditControl.ExportOptions.HtmlOptions.EmbedImages option.

Each image in the RichEditControl has the OfficeImage.Uri property that is the original image URI. To save an original image URI to the exported HTML document, our custom UriProvider returns the OfficeImage.Uri value.

Note

A complete sample project is available at https://github.com/DevExpress-Examples/dxrichedit-for-wpf-how-to-retain-original-image-uri-in-html-document-e3294.

CustomUriProvider.cs

using DevExpress.Office.Services;
using DevExpress.Office.Utils;
using System;
    public class CustomUriProvider : IUriProvider
    {
        public string CreateCssUri(string rootUri, string styleText, string relativeUri) {
            return String.Empty;
        }

        public string CreateImageUri(string rootUri, OfficeImage image, string relativeUri) {
            return image.Uri;
        }
    }

MainWindow.xaml.cs

using DevExpress.Office.Services;
using DevExpress.XtraRichEdit.API.Native;
        private void richEditControl1_DocumentLoaded(object sender, EventArgs e)
        {
            IUriProviderService service = richEditControl1.GetService<IUriProviderService>();
            if (service != null)
            {
                service.RegisterProvider(new CustomUriProvider());
            }
        }

MainWindow.xaml.vb

Imports DevExpress.Office.Services
Imports DevExpress.XtraRichEdit.API.Native
        Private Sub richEditControl1_DocumentLoaded(ByVal sender As Object, ByVal e As EventArgs)
            Dim service As IUriProviderService = richEditControl1.GetService(Of IUriProviderService)()
            If service IsNot Nothing Then
                service.RegisterProvider(New CustomUriProvider())
            End If
        End Sub

CustomUriProvider.vb

Imports DevExpress.Office.Services
Imports DevExpress.Office.Utils
Imports System
    Public Class CustomUriProvider
        Implements IUriProvider

        #Region "IUriProvider Members"
        Public Function CreateCssUri(ByVal rootUri As String, ByVal styleText As String, ByVal relativeUri As String) As String Implements IUriProvider.CreateCssUri
            Return String.Empty
        End Function

        Public Function CreateImageUri(ByVal rootUri As String, ByVal image As OfficeImage, ByVal relativeUri As String) As String Implements IUriProvider.CreateImageUri
            Return image.Uri
        End Function

Export the Result

The following table shows the different methods used to embed images and export the document to HTML format:

Export	Result
RichEditControl.HtmlText property	Images are contained in the resulting file as base64-encoded data.
SubDocument.GetHtmlText method	The HtmlDocumentExporterOptions parameter allows you to specify embedded or standalone images by setting the HtmlDocumentExporterOptions.EmbedImages property.
RichEditControl.SaveDocument or RichEditControl.SaveDocumentAs methods	The DXRichEditHtmlDocumentExporterOptions.EmbedImages property, accessible using the RichEditControl.ExportOptions.HtmlOptions.EmbedImages notation, determines whether images are embedded or saved as separate files. Specify this property in the RichEditControl.BeforeExport event handler.

The code sample below specifies the HtmlDocumentExporterOptions properties and retrieves the document content in HTML format.

Note

A complete sample project is available at https://github.com/DevExpress-Examples/dxrichedit-for-wpf-how-to-retain-original-image-uri-in-html-document-e3294.

C#

private void richEditControl1_ContentChanged(object sender, EventArgs e)
{
    ReloadHtml();
}

private void ReloadHtml()
{
    DevExpress.XtraRichEdit.Export.HtmlDocumentExporterOptions exportOptions = new DevExpress.XtraRichEdit.Export.HtmlDocumentExporterOptions();
    exportOptions.EmbedImages = (bool)embedImagesCheck.IsChecked;
    string sText = richEditControl1.Document.GetHtmlText(richEditControl1.Document.Range, new CustomUriProvider(), exportOptions);
    memoEdit1.Text = sText;
}

VB.NET

Private Sub richEditControl1_ContentChanged(ByVal sender As Object, ByVal e As EventArgs)
    ReloadHtml()
End Sub

Private Sub ReloadHtml()
    Dim exportOptions As New DevExpress.XtraRichEdit.Export.HtmlDocumentExporterOptions()
    exportOptions.EmbedImages = CBool(embedImagesCheck.IsChecked)
    Dim sText As String = richEditControl1.Document.GetHtmlText(richEditControl1.Document.Range, New CustomUriProvider(), exportOptions)
    memoEdit1.Text = sText
End Sub