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Once a file is uploaded to an App Token application, it can be previewed using two different methods:
  • Direct embed: A standard HTML <iframe> component with a custom embed link.
  • Customized previewer: A fully customized preview widget using Box UI Elements.

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Direct Embed (iframe)

The direct embed link provides limited options to customize the preview experience in your application. Due to the light-weight nature of the method, the API doesn’t give you options to respond to client-side actions such as scrolling in the case of documents, play/pause interactivity for videos, rotating an image, etc. There are two steps to create a direct <iframe> embed for Box View:
  1. Generate an embed URL for the file
  2. Add the embed URL to an <iframe>

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Generate an embed URL for the file

To create a public file preview URL for a file that was uploaded to the App Token application, you may either use a direct SDK method or make the request directly to the APIs.
When generating the embed URL directly from the APIs, use the Get File Information endpoint and request expiring_embed_link via the fields parameter.
curl https://api.box.com/2.0/files/FILE_ID?fields=expiring_embed_link \
    -H "authorization: Bearer [APP_TOKEN]"
Within the response object will be a public embed URL like the following: 
https://app.box.com/preview/expiring_embed/gvoct6FE!YT_X1LauQ8ulDTad96hTl9xLCRYJ
5iU6O61KxiduxFIgX9HSWMcCWf7zju1XkEsf6-Ul2qtKXeaFeKPT4SysQJQdxrc144KgTIBuoI3bWMf4
cfhp3jdLYrK5hnr6KMq5H6r-AW31AcFtDJi1lnT0M4b3bvvZUaE2RRJGGINMauvS6MAT2luae5PvbFSx
Ctqqx6XlN6QrqbhfJc0UeJF9qwMv3-O8q5fWn0qr8OTY4lkeYidtTs3Ux...
For security reasons, the generated embed link will expire after 1 minute and should be immediately embedded in the app once generated.

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Add the embed URL to an <iframe>

Within the HTML of your application, create an iframe elements with the src attribute set to generated embed URL. 
<iframe src="https://app.box.com/preview/expiring_embed/gvoct6FE!ixgtCKQAziW
  9tHPm-jueq4cmS4GnL9RTJRcVEsK_3W8xcxtVo_v6gKpoXY45odgG1QrcjBVYZMrriUyGvcoSM
  SX8s-smpaFFYQik0R-PCKFtwvbv0lonid6ZfYNbuNFl2j9hOIqBccvHrdVor7i6WvOm6zELzTY
  4EWshcyYYBhDbJmYMrq61RtU_kvBe5P..."></iframe>

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Customized Previewer (UI Elements)

To leverage advanced preview customization and event handling capabilities, use the Box UI Preview Element. To set up the Preview Element, start by installing the required components.

Install Box Elements and Preview

 The basic code will resemble the below when adding the JavaScript code to display a new previewer. 
var preview = new Box.Preview();
preview.show("FILE_ID", "ACCESS_TOKEN", {
    container: ".preview-container",
    showDownload: true
});
Replace the placeholders in the code sample with the following:
  • FILE_ID: The ID of the file uploaded to the App Token application, which can be obtained from the object returned when uploading the file.
  • ACCESS_TOKEN: The primary Access Token set up when configuring the application or a downscoped version of the token.
Due to the elevated privileges of the primary access token it’s highly recommended that you use a downscoped version of the token in the Javascript code. See best practices for downscoping.