Gemini AI Integration with ASP.NET Core Smart Paste Button

16 Dec 202515 minutes to read

The Syncfusion ASP.NET Core SmartPaste Button control enables AI-powered, context-aware content pasting into forms, typically using OpenAI or Azure OpenAI. This guide explains how to integrate the Google Gemini AI service with the Smart Paste Button using the IChatInferenceService interface, enabling custom AI-driven responses in a ASP.NET Core Web App.

Setting Up Gemini

Obtain a Gemini API Key
Visit Google AI Studio, sign in, and generate an API key.
Review Model Specifications
Refer to Gemini Models Documentation for details on available models.

Create a Gemini AI Service

Create a service class to manage interactions with the Gemini API, including authentication, request/response handling, and safety settings for the Smart Paste Button.

Create a Services folder in your project.
Add a new file named GeminiService.cs in the Services folder.
Implement the service as shown below, storing the API key securely in a configuration file or environment variable (e.g., appsettings.json).

using System.Net;
using System.Text;
using System.Text.Json;
using Microsoft.Extensions.AI;

public class GeminiService
{
    private readonly string _apiKey;
    private readonly string _modelName = "gemini-2.0-flash"; // Example model
    private readonly string _endpoint = "https://generativelanguage.googleapis.com/v1beta/models/";
    private static readonly HttpClient HttpClient = new(new SocketsHttpHandler
    {
        PooledConnectionLifetime = TimeSpan.FromMinutes(30),
        EnableMultipleHttp2Connections = true
    })
    {
        DefaultRequestVersion = HttpVersion.Version20 // Fallback to HTTP/2 for compatibility
    };
    private static readonly JsonSerializerOptions JsonOptions = new()
    {
        PropertyNamingPolicy = JsonNamingPolicy.CamelCase
    };

    public GeminiService(IConfiguration configuration)
    {
        _apiKey = configuration["Gemini:ApiKey"] ?? throw new ArgumentNullException("Gemini API key is missing.");
        HttpClient.DefaultRequestHeaders.Clear();
        HttpClient.DefaultRequestHeaders.Add("x-goog-api-key", _apiKey);
    }

    public async Task<string> CompleteAsync(IList<ChatMessage> chatMessages)
    {
        var requestUri = $"{_endpoint}{_modelName}:generateContent";
        var parameters = BuildGeminiChatParameters(chatMessages);
        var payload = new StringContent(
            JsonSerializer.Serialize(parameters, JsonOptions),
            Encoding.UTF8,
            "application/json"
        );

        try
        {
            using var response = await HttpClient.PostAsync(requestUri, payload);
            response.EnsureSuccessStatusCode();
            var json = await response.Content.ReadAsStringAsync();
            var result = JsonSerializer.Deserialize<GeminiResponseObject>(json, JsonOptions);
            return result?.Candidates?.FirstOrDefault()?.Content?.Parts?.FirstOrDefault()?.Text
                ?? "No response from model.";
        }
        catch (Exception ex) when (ex is HttpRequestException or JsonException)
        {
            throw new InvalidOperationException("Gemini API error.", ex);
        }
    }

    private GeminiChatParameters BuildGeminiChatParameters(IList<ChatMessage> messages)
    {
        var contents = messages.Select(m => new ResponseContent(
            m.Text,
            m.Role == ChatRole.User ? "user" : "model"
        )).ToList();

        return new GeminiChatParameters
        {
            Contents = contents,
            GenerationConfig = new GenerationConfig
            {
                MaxOutputTokens = 2000,
                StopSequences = new List<string> { "END_INSERTION", "NEED_INFO", "END_RESPONSE" } // Configurable stop sequences
            },
            SafetySettings = new List<SafetySetting>
            {
                new() { Category = "HARM_CATEGORY_HARASSMENT", Threshold = "BLOCK_ONLY_HIGH" },
                new() { Category = "HARM_CATEGORY_HATE_SPEECH", Threshold = "BLOCK_ONLY_HIGH" },
                new() { Category = "HARM_CATEGORY_SEXUALLY_EXPLICIT", Threshold = "BLOCK_ONLY_HIGH" },
                new() { Category = "HARM_CATEGORY_DANGEROUS_CONTENT", Threshold = "BLOCK_ONLY_HIGH" }
            }
        };
    }
}

NOTE

Store the Gemini API key in appsettings.json (e.g., { "Gemini": { "ApiKey": "your-api-key" } }) or as an environment variable to ensure security. The SafetySettings filter harmful content; adjust thresholds based on your application’s needs.

Define Request and Response Models

Define C# classes to match the Gemini API’s JSON request and response format.

Create a new file named GeminiModels.cs in the Services folder.
Add the following model classes:

public class Part
{
    public string Text { get; set; }
}

public class Content
{
    public Part[] Parts { get; init; } = Array.Empty<Part>();
}

public class Candidate
{
    public Content Content { get; init; } = new();
}

public class GeminiResponseObject
{
    public Candidate[] Candidates { get; init; } = Array.Empty<Candidate>();
}

public class ResponseContent
{
    public List<Part> Parts { get; init; }
    public string Role { get; init; }

    public ResponseContent(string text, string role)
    {
        Parts = new List<Part> { new Part { Text = text } };
        Role = role;
    }
}

public class GenerationConfig
{
    public int Temperature { get; init; } = 0;
    public int TopK { get; init; } = 0;
    public int TopP { get; init; } = 0;
    public int MaxOutputTokens { get; init; } = 2048;
    public List<string> StopSequences { get; init; } = new();
}

public class SafetySetting
{
    public string Category { get; init; } = string.Empty;
    public string Threshold { get; init; } = string.Empty;
}

public class GeminiChatParameters
{
    public List<ResponseContent> Contents { get; init; } = new();
    public GenerationConfig GenerationConfig { get; init; } = new();
    public List<SafetySetting> SafetySettings { get; init; } = new();
}

Create a Custom AI Service

Implement the IChatInferenceService interface to connect the Smart Paste Button to the Gemini service, acting as a bridge for AI-generated responses.

Create a new file named GeminiInferenceService.cs in the Services folder.
Add the following implementation:

using Syncfusion.EJ2.AI;
using System.Threading.Tasks;

public class GeminiInferenceService : IChatInferenceService
{
    private readonly GeminiService _geminiService;

    public GeminiInferenceService(GeminiService geminiService)
    {
        _geminiService = geminiService;
    }

    public async Task<string> GenerateResponseAsync(ChatParameters options)
    {
        return await _geminiService.CompleteAsync(options.Messages);
    }
}

Configure the ASP.NET Core App

Update the ~/Program.cs file as follows:

using Syncfusion.EJ2;
using Syncfusion.EJ2.AI;

builder.Services.AddRazorPages();

builder.Services.AddSyncfusionSmartComponents();
builder.Services.AddSingleton<GeminiService>();
builder.Services.AddSingleton<IChatInferenceService, GeminiInferenceService>();

var app = builder.Build();
// ...

Add the Smart Paste Button

Add the Smart Paste Button to a form in the ~/Pages/Index.cshtml file to test the Gemini AI integration.

CSHTML
<h1>Contact Form</h1>
<form action="/submit" method="post">
    <div class="mb-2">
        <label for="name" class="form-label">Full Name</label>
        <input type="text" class="form-control" id="name" name="name" required>
    </div>
    <div class="mb-2">
        <label for="email" class="form-label">Email</label>
        <input type="email" class="form-control" id="email" name="email" required>
    </div>
    <div class="mb-2">
        <label for="phone" class="form-label">Phone Number</label>
        <input type="tel" class="form-control" id="phone" name="phone">
    </div>
    <div class="mb-2">
        <label for="message" class="form-label">Message</label>
        <textarea class="form-control" id="message" name="message" rows="4"></textarea>
    </div>
    <div class="mb-2 form-check">
        <input type="checkbox" class="form-check-input" id="newsletter" name="newsletter" checked>
        <label class="form-check-label" for="newsletter">Subscribe to newsletter</label>
    </div>
    <div class="mb-2">
        <label class="form-label">Preferred Contact Method</label>
        <div class="form-check">
            <input type="radio" class="form-check-input" id="email-contact" name="contact" value="email">
            <label class="form-check-label" for="email-contact">Email</label>
        </div>
        <div class="form-check">
            <input type="radio" class="form-check-input" id="phone-contact" name="contact" value="phone">
            <label class="form-check-label" for="phone-contact">Phone</label>
        </div>
    </div>
    <div class="mb-2">
        <label for="country" class="form-label">Country</label>
        <select class="form-select" id="country" name="country">
            <option value="">Select Country</option>
            <option value="United States">United States</option>
            <option value="Canada">Canada</option>
            <option value="United Kingdom">United Kingdom</option>
        </select>
    </div>
    <button type="submit" class="btn btn-primary">Submit</button>
    <button type="reset" class="btn btn-secondary">Reset</button>
    <ejs-smartpaste id="smartPasteBtn" content="Smart Paste" cssClass="e-primary" iconCss="e-icons e-paste"></ejs-smartpaste>
</form>

<br />
<div>
    I am John Doe from the United States. My email is [email protected], and my phone number is 555-123-4567. I’d like to inquire about your services and have a detailed discussion regarding your product offerings. Please contact me via email. I’m happy to subscribe to your newsletter for updates. Thank you!
</div>

Press Ctrl+F5 (Windows) or ⌘+F5 (macOS) to run the app. Then, the Syncfusion^® ASP.NET Core
Smart Paste Button control will be rendered in the default web browser.

ASP.NET Core Smart Paste Button Control

Troubleshooting

If the Gemini AI integration does not work, try the following:

No Suggestions Displayed: Verify that the Gemini API key and model name are correct in the configuration. Check the GeminiService implementation for errors.
HTTP Request Failures: Ensure a stable internet connection and that the Gemini API endpoint (https://generativelanguage.googleapis.com/v1beta/models/) is accessible. Test with HTTP/2 if compatibility issues arise.
Service Registration Errors: Confirm that GeminiService and GeminiInferenceService are registered in Program.cs.

Search docs

Ask Syncfusion AI Assistant