Create an InputSelect component that accepts lists with Blazor

Question

With Blazor InputSelect you have iterate over list items in the component ChildContent but
I want to create a custom Blazor (WebAssembly version 5) InputSelect that could accept a list of any object to render in the select, the code could be like the followings :

<CustomInputSelect @bind-Value="@myEntity.CountryId" For="@(()=> myEntity.CountryId)" List="countries"
 ValueField="@(a => a.Id)" DisplayField="@(a => a.CountryName)" ></CustomInputSelect>

or even this :

<CustomInputSelect @bind-Value="@myEntity.Country" For="@(()=> myEntity.Country)" List="countries"
 ValueField="Id" DisplayField="CountryName" ></CustomInputSelect>

(Note: I used the For property to help compiler to infer the type of CountryId and also for validation. This is @typeparam of the component.)

I tried so many approaches but none of the worked so I explain them below:

• I tried using dynamic type for the list but it seems that Blazor does not supports dynamic types because there was error in razor generated code.

• I tried to use multiple @typeparam for the component, one for the value and one for the list items. And it seems that it does not support it either.

  @inherits InputSelect //or add another typeparam @typeparam TListItem

And

  <select>
                @foreach (var item in List)
                {
                   < option value="???">???</option >
                }
    </select> 
    
    @code{
     [Parameter] public Expression<Func<TValue>>? For { get; set; }
     [Parameter] public List<dynamic> List { get; set; }// or List<TListItem> 
     [Parameter] public Expression<Func<TListItem>>? ValueField { get; set; }
     [Parameter] public Expression<Func<string>>? DisplayField { get; set; }
    
    }

My goal is to send a list of any type to InputSelect while @typeparam is used for binding.

Answer 1

I've previous built and used this

@typeparam TItem
  <div class="form-control-wrapper">

    <select class="form-control-label" @onchange="ChangeHandler">
        @if (ShowDefaultOption)
        {
            <option value="0" hidden disabled>- Please Select -</option>
        }
        @foreach (var (id, item) in idDictionary)
        {
            <option value="@id">@Selector(item).ToString()</option>
        }
      </select>
    </div>
@code {

[Parameter] public IList<TItem> Items { get; set; }
[Parameter] public Func<TItem, object> Selector { get; set; }
[Parameter] public EventCallback<TItem> ValueChanged { get; set; }
[Parameter] public bool ShowDefaultOption { get; set; } = true;

private Dictionary<Guid, TItem> idDictionary;

protected override void OnInitialized()
{
    idDictionary = new Dictionary<Guid, TItem>();
    Items.ToList().ForEach(x => idDictionary.Add(Guid.NewGuid(), x));
}

private async Task ChangeHandler(ChangeEventArgs args)
{
    if (idDictionary.TryGetValue(Guid.Parse(args.Value.ToString()), out var selectedItem))
    {
        await ValueChanged.InvokeAsync(selectedItem);
    }
}
}

Then use can use it like this:

<MySelect ValueChanged="handleStringChange" TItem="string" Items="stringItems" Selector="(x => x)" />b
<p>@_selectedStringItem</p>


@code {

IList<string> stringItems = new List<string>()
{
    "Random",
    "String",
    "Content",
    "ForDemo"
};

string _selectedStringItem;
void handleStringChange(string value) => _selectedStringItem = value;
}

Or with an object:

<MySelect ValueChanged="handleChange" TItem="Person" Items="items" Selector="(x => x.Firstname)" />

@if (_selectedItem is object)
{
    <p>Selected person: Name: @_selectedItem.Firstname, Age: @_selectedItem.Age</p>
}

@code {
    class Person
    {
        public string Firstname { get; set; }
        public int Age { get; set; }
    }

    IList<Person> items = new List<Person>
    {
        new Person {Firstname = "John Doe", Age = 26},
        new Person {Firstname = "Jane Doe", Age = 23}
    };

    Person _selectedItem;

    void handleChange(Person value) => _selectedItem = value;
 }