Open and Save a Presentation in Google Cloud Storage

3 Aug 202618 minutes to read

Prerequisites

Google Cloud Storage is required.
A service account and its service account key are required.
The Google Cloud Storage API must be enabled in the Google Cloud Console. For steps, see Enable Google Cloud services.
The service account must be granted the Storage Object Viewer role (to download) and Storage Object Creator role (to upload) on the target bucket. For steps, see Manage access to buckets.
.NET 8.0 or later.
Place the downloaded service account key file (credentials.json) in the project root and set Copy to Output Directory to Copy if newer so the relative path resolves at runtime.

Open a Presentation from Google Cloud Storage

Steps to open a Presentation from Google Cloud Storage.

Step 1: Create an ASP.NET Core Web Application (Model-View-Controller).

Create an ASP.NET Core Web App project in Visual Studio

Step 2: Name the project.

Name the project

Step 3: Install the following NuGet packages in your application from NuGet.org.

Install Syncfusion.Presentation.Net.Core NuGet Package
Install Google.Cloud.Storage.V1 NuGet Package

Step 4: Add a new button to Index.cshtml as shown below.

CSHTML
@{Html.BeginForm("EditDocument", "Home", FormMethod.Get);
    {
        <div>
            <input type="submit" value="Edit Document" style="width:150px;height:27px" />
        </div>
    }
    Html.EndForm();
}

Step 5: Include the following namespaces in HomeController.cs.

C#
using System.IO;
using System.Threading.Tasks;
using Google.Apis.Auth.OAuth2;
using Google.Cloud.Storage.V1;
using Microsoft.AspNetCore.Mvc;
using Syncfusion.Presentation;

Step 6: Add the following code snippet to HomeController.cs to open a Presentation from Google Cloud Storage.

C#
public async Task<IActionResult> EditDocument()
{
    try
    {
        //Download the file from Google Cloud Storage
        MemoryStream memoryStream = await GetDocumentFromGoogle();

        //Save the downloaded file to a temp path so the path-based overload can be used
        string tempFilePath = Path.Combine(Path.GetTempPath(), "PowerPointTemplate.pptx");
        using (FileStream fileStream = new FileStream(tempFilePath, FileMode.Create, FileAccess.Write))
        {
            memoryStream.CopyTo(fileStream);
        }

        //Create an instance of the PowerPoint Presentation file using a file path
        using (IPresentation pptxDocument = Presentation.Open(tempFilePath))
        {
            //Get the first slide from the PowerPoint presentation
            ISlide slide = pptxDocument.Slides[0];

            //Get the first shape of the slide
            IShape shape = slide.Shapes[0] as IShape;

            //Change the text of the shape
            if (shape.TextBody.Text == "Company History")
                shape.TextBody.Text = "Company Profile";

            //Save the PowerPoint file to a path
            string outputPath = Path.Combine(Path.GetTempPath(), "EditPowerPoint.pptx");
            pptxDocument.Save(outputPath);

            //Read the saved file into a MemoryStream to return as a download
            MemoryStream outputStream = new MemoryStream();
            using (FileStream fileStream = new FileStream(outputPath, FileMode.Open, FileAccess.Read))
            {
                fileStream.CopyTo(outputStream);
            }
            outputStream.Position = 0;

            //Download the PowerPoint file in the browser
            FileStreamResult fileStreamResult = new FileStreamResult(outputStream, "application/powerpoint");
            fileStreamResult.FileDownloadName = "EditPowerPoint.pptx";
            return fileStreamResult;
        }
    }
    catch (FileNotFoundException ex)
    {
        return NotFound($"The specified Presentation was not found in the bucket: {ex.Message}");
    }
    catch (Google.GoogleApiException ex) when (ex.HttpStatusCode == System.Net.HttpStatusCode.Forbidden)
    {
        return StatusCode(403, "Access to the Google Cloud Storage bucket was denied. Verify the service account has the Storage Object Viewer role.");
    }
    catch (Exception ex)
    {
        return StatusCode(500, $"An error occurred while opening the Presentation: {ex.Message}");
    }
}

Download a file from Google Cloud Storage

This is the helper method to download a Presentation from Google Cloud Storage.

C#
/// <summary>
/// Download a file from Google Cloud Storage.
/// </summary>
/// <returns>A MemoryStream containing the file contents. The caller is responsible for disposing the returned stream.</returns>
public async Task<MemoryStream> GetDocumentFromGoogle()
{
    //Your bucket name
    string bucketName = "Your_bucket_name";

    //Your service account key file path (relative to the project output directory)
    string keyPath = "credentials.json";

    //Name of the file to download from the Google Cloud Storage bucket
    string fileName = "PowerPointTemplate.pptx";

    //Create Google Credential from the service account key file with the required scopes
    GoogleCredential credential = GoogleCredential.FromFile(keyPath)
        .CreateScoped(StorageClient.DefaultScopes);

    //Instantiate a storage client to interact with Google Cloud Storage
    StorageClient storageClient = await StorageClient.CreateAsync(credential);

    //Download a file from Google Cloud Storage
    MemoryStream memoryStream = new MemoryStream();
    await storageClient.DownloadObjectAsync(bucketName, fileName, memoryStream);
    memoryStream.Position = 0;

    return memoryStream;
}

You can download a complete working sample from GitHub.

By executing the program, you will get the PowerPoint presentation as follows.

Output Presentation

Save a Presentation to Google Cloud Storage

Steps to save a Presentation to Google Cloud Storage.