Generically-typed Parameters

Use @typeparam directive:

@typeparam TItem
<!-- or: -->
@typeparam TEntity where TEntity : IEntity

Example

Shared/ListGenericTypeItems.razor

<!-- This Component, ListGenericTypeItems, will be typed as TExample: -->
@typeparam TExample

@if (ExampleList is not null)
{
    <ul>
        @foreach (var item in ExampleList)
        {
            <li>@item</li>
        }
    </ul>
}

@code {
    [Parameter]
   
    public IEnumerable<TExample>? ExampleList{ get; set; }
}

This allows you to set the type parameter of a Component that renders a ListGenericTypeItems:
Pages/GenericTypeExample.razor

@page "/generic-type-example-1"

<h1>Generic Type Example 1</h1>

<ListGenericTypeItems ExampleList="@(new List<string> { "Item 1", "Item 2" })" 
                       TExample="string" />

<ListGenericTypeItems ExampleList="@(new List<int> { 1, 2, 3 })" 
                       TExample="int" />

Cascaded Generic Type Support

Add @attribute [CascadingTypeParameter(...)] to a Component. By doing so, the specified generic type argument is automatically used in descendant Components that: are nested as child content in the same .razor file; also declare a @typeparam with the exact same name; do not have another value explicitly supplied or implicitly inferred for that type parameter.

Notes:

Descendants obtain cascaded type parameter values from the closest ancestor that has a CascadingTypeParameterAttribute with a matching name.
Matching is only performed by name. For this reason, avoid cascaded generic type parameters with generic names like T or TItem.

For the following examples, consider the ListGenericTypeItems above and: Shared/ListDisplay.razor

@typeparam TExample

@if (ExampleList is not null)
{
    <ul style="color:blue">
        @foreach (var item in ExampleList)
        {
            <li>@item</li>
        }
    </ul>
}

@code {
    [Parameter]
    public IEnumerable<TExample>? ExampleList { get; set; }
}

Example: Explicit generic types based on ancestor Components

The GenericTypeExample2 Component sets the child content (RenderFragment) of two ListGenericTypeItems Components and specifies ListGenericTypeItems types (TExample) which are then cascaded to child Components, one with string data and one with integer data:

Pages/GenericTypeExample2.razor

@page "/generic-type-example-2"

<h1>Generic Type Example 2</h1>

<ListGenericTypeItems TExample="string">
    <ListDisplay ExampleList="@(new List<string> { "Item 1", "Item 2" })" />
    <ListDisplay ExampleList="@(new List<string> { "Item 3", "Item 4" })" />
</ListGenericTypeItems>

<ListGenericTypeItems TExample="int">
    <ListDisplay ExampleList="@(new List<int> { 1, 2, 3 })" />
    <ListDisplay ExampleList="@(new List<int> { 4, 5, 6 })" />
</ListGenericTypeItems>

Example: Infer generic types based on ancestor Components

This GenericTypeExample3 Component infers the type of ListGenericTypeItems: Pages/GenericTypeExample3.razor

@page "/generic-type-example-3"

<h1>Generic Type Example 3</h1>

<ListGenericTypeItems ExampleList="@(new List<string> { "Item 5", "Item 6" })">
    <ListDisplay1 ExampleList="@(new List<string> { "Item 1", "Item 2" })" />
    <ListDisplay2 ExampleList="@(new List<string> { "Item 3", "Item 4" })" />
</ListGenericTypeItems>

<ListGenericTypeItems ExampleList="@(new List<int> { 7, 8, 9 })">
    <ListDisplay1 ExampleList="@(new List<int> { 1, 2, 3 })" />
    <ListDisplay2 ExampleList="@(new List<int> { 4, 5, 6 })" />
</ListGenericTypeItems>