IUriStreamProvider Interface

Allows you to retirve data from a URI.

Namespace: DevExpress.Office.Services

Assembly: DevExpress.Office.v23.2.Core.dll

NuGet Packages: DevExpress.Office.Core, DevExpress.Win.Navigation

Declaration

C#

[ComVisible(true)]
public interface IUriStreamProvider

VB.NET

<ComVisible(True)>
Public Interface IUriStreamProvider

Remarks

To ensure that you load images and not just references to these images, create a custom class that implements the IUriStreamProvider interface. This applies to images loaded from:

• a database during the mail merge process
• an external source when an HTML or MHT file contains URIs to these images.

Create a custom class that implements the IUriStreamProvider interface, and customize its GetStream method. This method should return a stream with image data.

When your custom class is ready, call the IUriStreamService.RegisterProvider method to register this provider class.

Example

How to: Implement the IUriStreamProvider Service to Insert Images from a Data Source During Mail Merge

The code sample below shows the IUriStreamProvider implementation used to insert images from a database. The INCLUDEPICTURE field in the template has a nested MERGEFIELD that refers to the EmployeeID field from the database. The GetStream method parses the received URI (the INCLUDEPICTURE field) and finds the required data row, and returns the MemoryStream with an image.

Note

Make sure that the MERGEFIELD field nested in the INCLUDEPICTURE field in the template refers to the data table’s primary key. Otherwise, the IUriStreamProvider service cannot correctly find the required table row.

ImageStreamProvider.cs

using DevExpress.Office.Services;
using System;
using System.Data;
using System.IO;

public class ImageStreamProvider : IUriStreamProvider
{
    static readonly string prefix = "dbimg://";
    DataTable table;
    string columnName;

    public ImageStreamProvider(DataTable sourceTable, string imageColumn)
    {
        this.table = sourceTable;
        this.columnName = imageColumn;
    }


    public Stream GetStream(string uri)
    {
        // Parse the retrieved URI string
        uri = uri.Trim();
        if (!uri.StartsWith(prefix))
            return null;

        // Remove the prefix from the retrieved URI string
        string strId = uri.Substring(prefix.Length).Trim();
        int id;

        // Check if the string contains the primary key
        if (!int.TryParse(strId, out id))
            return null;

        // Retrieve the row that corresponds
        // with the key
        DataRow row = table.Rows.Find(id);
        if (row == null)
            return null;

        // Convert the image string from this row
        // to a byte array
        byte[] bytes = Convert.FromBase64String(row[columnName] as string) as byte[];
        if (bytes == null)
            return null;

        // Return the MemoryStream with an image
        MemoryStream memoryStream = new MemoryStream(bytes);
        return memoryStream;
    }
}

ImageStreamProvider.vb

Imports DevExpress.Office.Services
Imports System
Imports System.Data
Imports System.IO

Public Class ImageStreamProvider
    Inherits IUriStreamProvider

    Shared ReadOnly prefix As String = "dbimg://"
    Private table As DataTable
    Private columnName As String

    Public Sub New(ByVal sourceTable As DataTable, ByVal imageColumn As String)
        Me.table = sourceTable
        Me.columnName = imageColumn
    End Sub

    Public Function GetStream(ByVal uri As String) As Stream
        uri = uri.Trim()
        If Not uri.StartsWith(prefix) Then Return Nothing
        Dim strId As String = uri.Substring(prefix.Length).Trim()
        Dim id As Integer
        If Not Integer.TryParse(strId, id) Then Return Nothing
        Dim row As DataRow = table.Rows.Find(id)
        If row Is Nothing Then Return Nothing
        Dim bytes As Byte() = TryCast(Convert.FromBase64String(TryCast(row(columnName), String)), Byte())
        If bytes Is Nothing Then Return Nothing
        Dim memoryStream As MemoryStream = New MemoryStream(bytes)
        Return memoryStream
    End Function
End Class