description: Learn how templated components can accept one or more UI templates as parameters, which can then be used as part of the component's rendering logic.
Templated components are components that accept one or more UI templates as parameters, which can then be used as part of the component's rendering logic. Templated components allow you to author higher-level components that are more reusable than regular components. A couple of examples include:
* A table component that allows a user to specify templates for the table's header, rows, and footer.
* A list component that allows a user to specify a template for rendering items in a list.
A templated component is defined by specifying one or more component parameters of type <xref:Microsoft.AspNetCore.Components.RenderFragment> or <xref:Microsoft.AspNetCore.Components.RenderFragment%601>. A render fragment represents a segment of UI to render. <xref:Microsoft.AspNetCore.Components.RenderFragment%601> takes a type parameter that can be specified when the render fragment is invoked.
Often, templated components are generically typed, as the following `TableTemplate` component demonstrates. The generic type `<T>` in this example is used to render `IReadOnlyList<T>` values, which in this case is a series of pet rows in a component that displays a table of pets.
When using a templated component, the template parameters can be specified using child elements that match the names of the parameters. In the following example, `<TableHeader>...</TableHeader>` and `<RowTemplate>...<RowTemplate>` supply <xref:Microsoft.AspNetCore.Components.RenderFragment%601> templates for `TableHeader` and `RowTemplate` of the `TableTemplate` component.
Specify the `Context` attribute on the component element when you want to specify the content parameter name for implicit child content (without any wrapping child element). In the following example, the `Context` attribute appears on the `TableTemplate` element and applies to all <xref:Microsoft.AspNetCore.Components.RenderFragment%601> template parameters.
Alternatively, you can change the parameter name using the `Context` attribute on the <xref:Microsoft.AspNetCore.Components.RenderFragment%601> child element. In the following example, the `Context` is set on `RowTemplate` rather than `TableTemplate`:
Component arguments of type <xref:Microsoft.AspNetCore.Components.RenderFragment%601> have an implicit parameter named `context`, which can be used. In the following example, `Context` isn't set. `@context.{PROPERTY}` supplies pet values to the template, where `{PROPERTY}` is a `Pet` property:
When using generic-typed components, the type parameter is inferred if possible. However, you can explicitly specify the type with an attribute that has a name matching the type parameter, which is `TItem` in the preceding example:
## Infer generic types based on ancestor components
An ancestor component can cascade a type parameter by name to descendants using the `CascadingTypeParameter` attribute. This attribute allows a generic type inference to use the specified type parameter automatically with descendants that have a type parameter with the same name.
For example, the following `Chart` component receives stock price data and cascades a generic type parameter named `TLineData` to its descendent components.
> The Razor support in Visual Studio Code hasn't been updated to support this feature, so you may receive incorrect errors even though the project correctly builds. This will be addressed in an upcoming tooling release.
By adding `@attribute [CascadingTypeParameter(...)]` to a component, the specified generic type argument is automatically used by descendants that:
* Are nested as child content for the component in the same `.razor` document.
* Also declare a [`@typeparam`](xref:mvc/views/razor#typeparam) with the exact same name.
* Don't have another value supplied or inferred for the type parameter. If another value is supplied or inferred, it takes precedence over the cascaded generic type.
When receiving a cascaded type parameter, components obtain the parameter value from the closest ancestor that has a `CascadingTypeParameter` with a matching name. Cascaded generic type parameters are overridden within a particular subtree.
Matching is only performed by name. Therefore, we recommend avoiding a cascaded generic type parameter with a generic name, for example `T` or `TItem`. If a developer opts into cascading a type parameter, they're implicitly promising that its name is unique enough not to clash with other cascaded type parameters from unrelated components.
Generic types with [`where`](/dotnet/csharp/language-reference/keywords/where-generic-type-constraint) type constraints are supported:
Templated components are components that accept one or more UI templates as parameters, which can then be used as part of the component's rendering logic. Templated components allow you to author higher-level components that are more reusable than regular components. A couple of examples include:
* A table component that allows a user to specify templates for the table's header, rows, and footer.
* A list component that allows a user to specify a template for rendering items in a list.
A templated component is defined by specifying one or more component parameters of type <xref:Microsoft.AspNetCore.Components.RenderFragment> or <xref:Microsoft.AspNetCore.Components.RenderFragment%601>. A render fragment represents a segment of UI to render. <xref:Microsoft.AspNetCore.Components.RenderFragment%601> takes a type parameter that can be specified when the render fragment is invoked.
Often, templated components are generically typed, as the following `TableTemplate` component demonstrates. The generic type `<T>` in this example is used to render `IReadOnlyList<T>` values, which in this case is a series of pet rows in a component that displays a table of pets.
When using a templated component, the template parameters can be specified using child elements that match the names of the parameters. In the following example, `<TableHeader>...</TableHeader>` and `<RowTemplate>...<RowTemplate>` supply <xref:Microsoft.AspNetCore.Components.RenderFragment%601> templates for `TableHeader` and `RowTemplate` of the `TableTemplate` component.
Specify the `Context` attribute on the component element when you want to specify the content parameter name for implicit child content (without any wrapping child element). In the following example, the `Context` attribute appears on the `TableTemplate` element and applies to all <xref:Microsoft.AspNetCore.Components.RenderFragment%601> template parameters.
Alternatively, you can change the parameter name using the `Context` attribute on the <xref:Microsoft.AspNetCore.Components.RenderFragment%601> child element. In the following example, the `Context` is set on `RowTemplate` rather than `TableTemplate`:
Component arguments of type <xref:Microsoft.AspNetCore.Components.RenderFragment%601> have an implicit parameter named `context`, which can be used. In the following example, `Context` isn't set. `@context.{PROPERTY}` supplies pet values to the template, where `{PROPERTY}` is a `Pet` property:
When using generic-typed components, the type parameter is inferred if possible. However, you can explicitly specify the type with an attribute that has a name matching the type parameter, which is `TItem` in the preceding example:
Templated components are components that accept one or more UI templates as parameters, which can then be used as part of the component's rendering logic. Templated components allow you to author higher-level components that are more reusable than regular components. A couple of examples include:
* A table component that allows a user to specify templates for the table's header, rows, and footer.
* A list component that allows a user to specify a template for rendering items in a list.
A templated component is defined by specifying one or more component parameters of type <xref:Microsoft.AspNetCore.Components.RenderFragment> or <xref:Microsoft.AspNetCore.Components.RenderFragment%601>. A render fragment represents a segment of UI to render. <xref:Microsoft.AspNetCore.Components.RenderFragment%601> takes a type parameter that can be specified when the render fragment is invoked.
Often, templated components are generically typed, as the following `TableTemplate` component demonstrates. The generic type `<T>` in this example is used to render `IReadOnlyList<T>` values, which in this case is a series of pet rows in a component that displays a table of pets.
When using a templated component, the template parameters can be specified using child elements that match the names of the parameters. In the following example, `<TableHeader>...</TableHeader>` and `<RowTemplate>...<RowTemplate>` supply <xref:Microsoft.AspNetCore.Components.RenderFragment%601> templates for `TableHeader` and `RowTemplate` of the `TableTemplate` component.
Specify the `Context` attribute on the component element when you want to specify the content parameter name for implicit child content (without any wrapping child element). In the following example, the `Context` attribute appears on the `TableTemplate` element and applies to all <xref:Microsoft.AspNetCore.Components.RenderFragment%601> template parameters.
Alternatively, you can change the parameter name using the `Context` attribute on the <xref:Microsoft.AspNetCore.Components.RenderFragment%601> child element. In the following example, the `Context` is set on `RowTemplate` rather than `TableTemplate`:
Component arguments of type <xref:Microsoft.AspNetCore.Components.RenderFragment%601> have an implicit parameter named `context`, which can be used. In the following example, `Context` isn't set. `@context.{PROPERTY}` supplies pet values to the template, where `{PROPERTY}` is a `Pet` property:
When using generic-typed components, the type parameter is inferred if possible. However, you can explicitly specify the type with an attribute that has a name matching the type parameter, which is `TItem` in the preceding example:
