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EnumParameter\<T>

EnumParameter<T> is a transparent wrapper struct that allows Blazor component parameters to accept both enum values and plain strings. This eliminates the most common migration friction point: the Razor compiler requiring @() expression syntax for enum values.

Original Web Forms controls accepted string attribute values and parsed them at runtime. Blazor's strongly-typed parameter binding normally requires explicit enum syntax. EnumParameter<T> bridges this gap.

Background

In ASP.NET Web Forms, you could write:

<asp:GridView GridLines="None" runat="server" />
<asp:Panel ScrollBars="Vertical" runat="server" />

Web Forms parsed the string "None" into the GridLines enum at runtime. In Blazor, enum parameters normally require Razor expression syntax:

@* Without EnumParameter — requires wrapping in @() *@
<GridView GridLines="@(GridLines.None)" />
<Panel ScrollBars="@(ScrollBars.Vertical)" />

This means every migrated page needs manual touch-up of enum attributes, which is error-prone at scale.

How It Works

With EnumParameter<T>, both syntaxes work:

@* String value — just like Web Forms *@
<GridView GridLines="None" />
<Panel ScrollBars="Vertical" />

@* Enum value — standard Blazor syntax still works *@
<GridView GridLines="@(GridLines.None)" />

The wrapper provides implicit conversions in both directions:

  • string → EnumParameter<T>: Parses the string (case-insensitive) into the enum value
  • T → EnumParameter<T>: Wraps the enum value directly
  • EnumParameter<T> → T: Unwraps back to the original enum transparently

Supported Components

EnumParameter<T> is used across 46 components in the library, covering all enum parameters:

Component Parameters
GridView GridLines, SortDirection, HorizontalAlign
DetailsView GridLines, HorizontalAlign
Panel ScrollBars, HorizontalAlign, Direction
TextBox TextMode
Calendar DayNameFormat, FirstDayOfWeek, NextPrevFormat, TitleFormat
BulletedList BulletStyle, DisplayMode
UpdatePanel UpdateMode, RenderMode
ScriptManager ScriptMode
Login Orientation
Localize Mode
...and many more

Usage Notes

In Migrated Markup

No changes needed — string enum values from Web Forms work as-is:

<GridView DataSource="@products"
          GridLines="Both"
          HorizontalAlign="Center"
          AutoGenerateColumns="true" />

In Code-Behind

When comparing EnumParameter<T> values in C# code, the implicit conversion handles most cases:

@code {
    // Direct comparison works via implicit conversion
    private EnumParameter<GridLines> _gridLines = GridLines.None;

    private void CheckGridLines()
    {
        if (_gridLines == GridLines.None) { /* works */ }
    }
}

Switch Statements

C# pattern matching does not use implicit conversions. In switch statements, use .Value:

switch (gridLines.Value)  // Not: switch (gridLines)
{
    case GridLines.None: break;
    case GridLines.Both: break;
}

Shouldly / Test Assertions

Some assertion libraries don't resolve extension methods for generic structs. Use .Value in test assertions:

cut.Instance.GridLines.Value.ShouldBe(GridLines.None);  // ✓
// cut.Instance.GridLines.ShouldBe(GridLines.None);      // ✗ won't compile

Invalid Values

If an invalid string is passed, EnumParameter<T> throws an ArgumentException at parameter binding time:

@* This will throw ArgumentException — "Invalid" is not a GridLines value *@
<GridView GridLines="Invalid" />

Moving On

EnumParameter<T> is a migration convenience. As you modernize your Blazor application:

  1. Keep string syntax if it improves readability — there's no performance penalty
  2. Switch to enum syntax (@(GridLines.None)) when you want compile-time safety and IDE IntelliSense
  3. The wrapper has zero runtime overhead for enum-value assignments; string parsing only occurs for string-value assignments

See Also