Using Blazor, rendering <select> elements in a for loop and can't get @bind to work with a dictionary by index

Question

Let's define the dictionary I'm using as searchBoardGames[image.Id]

The select is in a foreach loop so I can render multiple select elements because what I'm trying to do is collect data from the user for multiple entries, but using the same list of gameIds. The @foreach loop with the <select> would be something like this:

<div class="image-gallery">
    @foreach (var image in images)
    {
        <div class="image-item">
            <img src="data:image/png;base64,@Convert.ToBase64String(image.ImageData)" alt="Unknown Image" />
            <div id="boardGameSelect" class="board-game-select">
                @if (searchResults.ContainsKey(image.Id) && searchResults[image.Id].Any())
                {
                    <select id="@selectInputId" @bind="searchBoardGames[image.Id]">
                        <option value="">-- Select a Board Game --</option>
                        @foreach (var game in searchResults[image.Id])
                        {
                            <option value="@game.Id">@game.Name</option>
                        }
                    </select>
                }
            </div>
        </div>
    }
</div>

So now the problem is the @bind=searchBoardGames[image.Id] isn't going to work, but I can't figure out how to get around this problem. I can't add an @onchange because that's used by @bind and I haven't been able to construct a method that could return something because it needs to be bound to a Property, not the value of some returned variable.

Answer 1

You can use @onchange to manually handle the changes for each <select>, since @bind can't directly bind to a dictionary key. A whole working demo you could follow:

@page "/"
@rendermode InteractiveServer
<form method="post" @onsubmit="HandleValidSubmit" @formname="TestForm">
    <div class="image-gallery">
        @foreach (var image in images)
        {
            <div class="image-item">
                <img src="data:image/png;base64,@Convert.ToBase64String(image.ImageData)" alt="Unknown Image" />
                <div id="boardGameSelect" class="board-game-select">
                    @if (searchResults.ContainsKey(image.Id) && searchResults[image.Id].Any())
                    {
                        <select id="select-@image.Id" value="@GetSelectedValue(image.Id)" @onchange="(e) => UpdateSelectedGame(image.Id, e.Value)">
                            <option value="">-- Select a Board Game --</option>
                            @foreach (var game in searchResults[image.Id])
                            {
                                <option value="@game.Id">@game.Name</option>
                            }
                        </select>
                    }
                </div>
            </div>
        }
    </div>

    <button type="submit">Submit</button>
</form>

@code {
    // Dictionary to hold the selected board game for each image
    private Dictionary<int, string> searchBoardGames = new Dictionary<int, string>();

    // List of images (you can replace this with your actual model for images)
     List<ImageModel> images = new List<ImageModel>
    {
        new ImageModel { Id = 1, ImageData =new byte[0] }, // Sample image
        new ImageModel { Id = 2, ImageData = new byte[0]}   // Sample image
    };

    // Dictionary that stores search results for board games per image ID
    private Dictionary<int, List<GameModel>> searchResults = new Dictionary<int, List<GameModel>>
    {
        { 1, new List<GameModel> { new GameModel { Id = "g1", Name = "Catan" }, new GameModel { Id = "g2", Name = "Ticket to Ride" } } },
        { 2, new List<GameModel> { new GameModel { Id = "g3", Name = "Pandemic" }, new GameModel { Id = "g4", Name = "Carcassonne" } } }
    };

    // Method to get the selected value for the current image
    private string GetSelectedValue(int imageId)
    {
        if (searchBoardGames.ContainsKey(imageId))
        {
            return searchBoardGames[imageId];
        }
        return "";
    }

    // Method to update the selected board game for an image
    private void UpdateSelectedGame(int imageId, object selectedGameId)
    {
        if (!string.IsNullOrEmpty(selectedGameId?.ToString()))
        {
            searchBoardGames[imageId] = selectedGameId.ToString();
        }
    }
    private void HandleValidSubmit()
    {
        // Process the selected board games
        foreach (var entry in searchBoardGames)
        {
            Console.WriteLine($"Image {entry.Key} has selected game ID: {entry.Value}");
        }
    }
    // Sample models
    public class ImageModel
    {
        public int Id { get; set; }
        public byte[] ImageData { get; set; }
    }

    public class GameModel
    {
        public string Id { get; set; }
        public string Name { get; set; }
    }
}