Gemini AI Integration with ASP.NET Core Smart TextArea

14 May 202612 minutes to read

The Syncfusion ASP.NET Core Smart TextArea control provides AI-powered autocompletion for context-aware text input, typically using OpenAI or Azure OpenAI. This guide explains how to integrate the Google Gemini AI service with the Smart TextArea 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 TextArea.

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 TextArea 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 ASP.NET Core Smart TextArea Control

Add the Smart TextArea in the ~/Pages/Index.cshtml file to test the Gemini AI integration.

CSHTML
@{
    var presets = new { 
        userRole = "Maintainer of an open-source project replying to GitHub issues",
        userPhrases = new[] { "Thank you for contacting us.", "To investigate, we'll need a repro as a public Git repo.", "Could you please post a screenshot of NEED_INFO?", "This sounds like a usage question. This issue tracker is intended for bugs and feature proposals. Unfortunately, we don't have the capacity to answer general usage questions and would recommend StackOverflow for a faster response.", "We don't accept ZIP files as repros." }, 
        placeHolder = "Write your response to the GitHub issue..." };
}

<ejs-smarttextarea id="smartTextarea" user-role="@presets.userRole" user-phrases="@presets.userPhrases" width="75%" placeholder="@presets.placeHolder" floatLabelType="Auto" rows="5"></ejs-smarttextarea>

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

ASP.NET Core Smart TextArea 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.

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