How to Set Selected Value in MVC5 Razor `Html.DropDownListFor` when Value is in an Array?

Setting Selected Values in MVC5 Razor Html.DropDownListFor with Array Values

Working with arrays and @Html.DropDownListFor() in ASP.NET MVC 5 to select values can be tricky. Here are two approaches to overcome this challenge:

Method 1: Leveraging EditorTemplates

This method involves creating a dedicated EditorTemplate for the collection's data type. The SelectList is then passed to the EditorTemplate as additional ViewData.

<code class="language-csharp">// AggregationLevelConfiguration.cshtml (EditorTemplate)
@Html.DropDownListFor(m => m.HelperCodeType, (SelectList)ViewData["CodeTypeItems"])

// Main View
@Html.EditorFor(m => m.Configurations, new { CodeTypeItems = Model.CodeTypeItems })</code>

This approach cleanly separates the dropdown logic from the main view, improving maintainability.

Method 2: Dynamic SelectList Generation

Alternatively, you can replace IEnumerable properties with IEnumerable<GenericIdNameType> (replace GenericIdNameType with your actual type). Then, iterate through the array in your main view, creating a new SelectList for each item and setting the selected value accordingly.

<code class="language-csharp">// Main View
@for (int i = 0; i < Model.Configurations.Count(); i++)
{
    @Html.DropDownListFor(m => m.Configurations[i].HelperCodeType, 
                           new SelectList(Model.CodeTypeItems, "Id", "Name", Model.Configurations[i].HelperCodeType))
}</code>

This method is more direct but can become less manageable with larger arrays. Consider using a helper method to encapsulate the SelectList creation for better readability if you choose this approach. Remember to adjust "Id" and "Name" to match your actual properties.

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