The DropDownList component is too basic to be used in complex environments. In the real world, no one is binding DropDownLists to List<string>, they are binding to complex datatypes, and the ability to do so has been present in MVC apps for a long time.
Given the following code, it is possible to bind to a List<object>, and two-way bind to the object that was selected.
<select @onchange="@OnChangedAsync">
<option></option>
@if (DataSource != null)
{
@foreach (var item in DataSource)
{
<option @key="item" value="@optionValueFunc(item)" selected="@(item.Equals(SelectedItem))">@optionTextFunc(item)</option>
}
}
</select>
#region Private Members
private Func<TSource, object> optionTextFunc;
private Func<TSource, object> optionValueFunc;
private TSource selectedItem = default(TSource);
#endregion
#region Public Parameters
/// <summary>
/// A List of objects to bind against.
/// </summary>
[Parameter]
public IList<TSource> DataSource { get; set; } = new List<TSource>();
/// <summary>
/// A lambda expression referencing the property containing the text to display to the end user. Example: @(c => c.DisplayName)
/// </summary>
[Parameter]
public Expression<Func<TSource, object>> OptionText { get; set; }
/// <summary>
/// A lambda expression referencing the property containing the value for this object, usually an identifier. Example: @(c => c.Id)
/// </summary>
[Parameter]
public Expression<Func<TSource, object>> OptionValue { get; set; }
/// <summary>
/// The item from the <see cref="DataSource" /> that has been selected.
/// </summary>
[Parameter]
public TSource SelectedItem { get; set; }
/// <summary>
/// The callback event required for two-way binding.
/// </summary>
[Parameter]
public EventCallback<TSource> SelectedItemChanged { get; set; }
#endregion
private async Task OnChangedAsync(ChangeEventArgs changeEventArgs)
{
await UpdateSelection(DataSource.FirstOrDefault(c => optionValueFunc(c).ToString() == changeEventArgs.Value.ToString()));
}
private async Task UpdateSelection(TSource item)
{
selectedItem = item;
await SelectedItemChanged.InvokeAsync(selectedItem);
}
protected override async Task OnInitializedAsync()
{
if (optionTextFunc == null && OptionText != null)
{
optionTextFunc = OptionText.Compile();
}
if (optionValueFunc == null && OptionText != null)
{
optionValueFunc = OptionValue.Compile();
}
await Task.CompletedTask;
}
Would really appreciate it if you would consider adding this to the next release.
This will allow the dropdown to be large enough to fit a reasonable number of items without a scrollbar. Alternatively, you could limit it through a pixel value you can set, or through the MaxPopupHeight property if it gets implemented: https://feedback.telerik.com/blazor/1412653-maxpopupheight.