See the example below to see how a value can be added or changed programmatically. To update a value of this property editor you need the Content Service and the Media Service.
The example below demonstrates how to add values programmatically using a Razor view. However, this is used for illustrative purposes only and is not the recommended method for production environments.
If Models Builder is enabled you can get the alias of the desired property without using a magic string:
@using System.Net
@using Umbraco.Cms.Core
@using Umbraco.Cms.Core.Services
@using Umbraco.Cms.Core.PropertyEditors
@using Umbraco.Cms.Core.IO
@using Umbraco.Cms.Core.Serialization
@using Umbraco.Cms.Core.Strings
@inject MediaFileManager MediaFileManager
@inject IShortStringHelper ShortStringHelper
@inject IContentTypeBaseServiceProvider ContentTypeBaseServiceProvider
@inject IContentService ContentService
@inject IMediaService MediaService
@inject IJsonSerializer Serializer
@inject MediaUrlGeneratorCollection MediaUrlGeneratorCollection
@{
// Create a variable for the GUID of the parent where you want to add a child item
var guid = Guid.Parse("32e60db4-1283-4caa-9645-f2153f9888ef");
// Get the page using the GUID you've defined
var content = ContentService.GetById(guid); // ID of your page
// Create a variable for the file you want to upload, in this case the Our Umbraco logo
var imageUrl = "https://our.umbraco.com/assets/images/logo.svg";
// Create a request to get the file
var request = WebRequest.Create(imageUrl);
var webResponse = request.GetResponse();
var responseStream = webResponse.GetResponseStream();
// Get the file name
var lastIndex = imageUrl.LastIndexOf("/", StringComparison.Ordinal) + 1;
var filename = imageUrl.Substring(lastIndex, imageUrl.Length - lastIndex);
// Create a media file
var media = MediaService.CreateMediaWithIdentity("myImage", -1, "File");
media.SetValue(MediaFileManager, MediaUrlGeneratorCollection, ShortStringHelper, ContentTypeBaseServiceProvider, Constants.Conventions.Media.File, filename, responseStream);
// Save the created media
MediaService.Save(media);
// Get the published version of the media (IPublishedContent)
var publishedMedia = Umbraco.Media(media.Id);
// Set the value of the property with alias 'myFile'
content.SetValue("myFile", publishedMedia.Url());
// Save the child item
ContentService.Save(content);
}
@using Umbraco.Cms.Core.PublishedCache
@inject IPublishedContentTypeCache PublishedContentTypeCache
@{
// Set the value of the property with alias 'myFile'
content.SetValue(Home.GetModelPropertyType(PublishedContentTypeCache, x => x.MyFile).Alias, publishedMedia.Url();
}