Web-Components.md

View components are similar to page views, but they're much more powerful. View components don't use model binding and only depend on the data provided when calling into it.

A view component:

• Renders a chunk rather than a whole response.
• Includes the same separation-of-concerns and testability benefits found between a controller and view.
• Can have parameters and business logic.
• Is typically invoked from a layout page.

View components are intended anywhere you have reusable rendering logic that's too complex for a partial view, such as:

• Dynamic navigation menus
• Tag cloud (where it queries the database)
• Login panel
• Shopping cart
• Recently published articles
• Sidebar content on a typical blog
• A login panel that would be rendered on every page and show either the links to log out or log in, depending on the login state of the user

A view component consists of two parts: the class (typically derived from ViewComponent) and the result it returns (typically a view). Like controllers, a view component can be a POCO, but most developers will want to take advantage of the methods and properties available by deriving from ViewComponent.

Creating a view component

A view component class can be created on your ABS Instance administration dashboard, under Appearance > Components.

View component methods

A view component defines its logic in an InvokeAsync method that returns a Task<IViewComponentResult> or in a synchronous Invoke method that returns an IViewComponentResult. Parameters come directly from the invocation of the view component, not from model binding. A view component never directly handles a request. Typically, a view component initializes a model and passes it to it's corresponding view by calling the View method. In summary, view component methods:

• Define an InvokeAsync method that returns a Task<IViewComponentResult> or a synchronous Invoke method that returns an IViewComponentResult.
• Typically initializes a model and passes it to a view by calling the ViewComponent View method.
• Parameters come from the calling method, not HTTP. There's no model binding.
• Are not reachable directly as an HTTP endpoint. They're invoked from your code (usually in view). A view component never handles a request.
• Are overloaded on the signature rather than any details from the current HTTP request.

View search path

The Alliance Business Suite searches for ViewComponents using the Alliance Business Model Schema. It will use case insensitive search by Name and Id for the ViewComponent.

Note: If the View Component is not rendered, no errors will be thrown and only an empty markup string will be rendered.

Perform synchronous work

The framework handles invoking a synchronous Invoke method if you don't need to perform asynchronous work. The following method creates a synchronous Invoke view component:

public class Template : DynamicComponentBase
{
    public dynamic Invoke(int maxPriority, bool isDone)
    {
        var items = new List<string> { $"maxPriority: {maxPriority}", $"isDone: {isDone}" };
        return items;
    }
}

A view component class:

• Fully supports constructor dependency injection

• Doesn't take part in the controller lifecycle, which means you can't use filters in a view component

@model List<string>

<h3>Priority Items</h3>
<ul>
    @foreach (var item in Model)
    {
        <li>@item</li>
    }
</ul>

Invoking a Web Component

To use a component inside a Page, template, or another component, call ViewService.InvokeAsync from anywhere in your view:

@await ViewService.InvokeAsync("Component Name or Id", {Anonymous Type Containing Parameters}, (optional) recompile = false)

@await ViewService.InvokeAsync("Component Name or Id", new { maxPriority = 1, isDone = false  })

All view component parameters are required

Each parameter in a view component is a required attribute. See this GitHub issue. If any parameter is omitted:

• The InvokeAsync method signature won't match, therefore the method won't execute.
• The ViewComponent won't render any markup.
• No errors will be thrown.