How to: Retain the Image URI in an HTML Document

• May 05, 2018
• 3 minutes to read

This example provides more details on exporting to HTML 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 table below describes the two options for saving images when saving a document as HTML.

Option	HTML Sample
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;" />

The following table shows the different methods and their results:

Export	Result
RichEditControl.HtmlText property	Images are contained in the resulting file as base64-encoded data.
SubDocument.GetHtmlText method	The HtmlDocumentExporterOptions parameter allows specifying embedded or standalone images by setting the HtmlExportOptionsBase.EmbedImagesInHTML property.
RichEditControl.SaveDocument or RichEditControl.SaveDocumentAs methods, the SaveDocumentAsCommand command	The DXRichEditHtmlDocumentExporterOptions.EmbedImages property, accessible using the RichEditControl.ExportOptions.HtmlOptions.EmbedImages notation, determines whether images are embedded or saved as separate files.

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.

When the document is saved to HTML, the built-in URI provider creates links to image files, as illustrated in the following table. A custom URI provider implemented in this example allows you to link images to their original URIs.

Provider	HTML
Built-in FileBasedUriProvider	HTML <img src="test_files/image0.png" alt="" style="border-width:0px;" />
CustomUriProvider	HTML <img src="http://www.devexpress.com/i/pagetitles/xtrarichedit.png" width="260" height="90" alt="" style="border-width:0px;" />

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.

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

CustomUriProvider.cs

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

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

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());
            }
        }