Users of the pizza store can now track the status of their orders in real time. In this session we'll use JavaScript interop to add a real-time map to the order status page that answers the age old question, "Where's my pizza?!?".
Included in the ComponentsLibrary project is a prebuilt Map component for displaying the location of a set of markers and animating their movements over time. We'll use this component to show the location of the user's pizza orders as they are being delivered, but first let's look at how the Map component is implemented.
Open Map.razor located in the Map folder of the BlazingPizza.ComponentLibrary project and take a look at the code:
The Map component uses dependency injection to get an IJSRuntime instance. This service can be used to make JavaScript calls to browser APIs or existing JavaScript libraries by calling the InvokeVoidAsync or InvokeAsync<TResult> method. The first parameter to this method specifies the path to the JavaScript function to call relative to the root window object. The remaining parameters are arguments to pass to the JavaScript function. The arguments are serialized to JSON so they can be handled in JavaScript.
The Map component first renders a div with a unique ID for the map and then calls the deliveryMap.showOrUpdate function to display the map in the specified element with the specified markers passed to the Map component. This is done in the OnAfterRenderAsync component lifecycle event to ensure that the component is done rendering its markup. The deliveryMap.showOrUpdate function is defined in the wwwroot/deliveryMap.js file, which then uses leaflet.js and OpenStreetMap to display the map. The details of how this code works isn't really important - the critical point is that it's possible to call any JavaScript function this way.
How do these files make their way to the Blazor app? For a Blazor library project (using Sdk="Microsoft.NET.Sdk.Razor") any files in the wwwroot/ folder will be bundled with the library. The server project will automatically serve these files using the static files middleware.
The final link is for the page hosting the Blazor client app to include the desired files (in our case .js and .css). The index.html includes these files using relative URIs like _content/BlazingPizza.ComponentsLibrary/localStorage.js. This is the general pattern for references files bundled with a Blazor class library - _content/<library name>/<file path>.
If you start typing in Map, you'll notice that the editor doesn't offer completion for it. This is because the binding between elements and components are governed by C#'s namespace binding rules. The Map component is defined in the BlazingPizza.ComponentsLibrary.Map namespace, which we don't have an @using for.
Add an @using for this namespace to the _Imports.razor file in the BlazingPizza.client project to bring this component into scope:
@using BlazingPizza.ComponentsLibrary.Map
Add the Map component to the OrderDetails.razor file in the Pages folder of the BlazingPizza.client project by adding the following just below the track-order-details div:
<div class="track-order-map">
<Map Zoom="13" Markers="orderWithStatus.MapMarkers" />
</div>
The reason why we haven't needed to add @usings for our components before now is that our root _Imports.razor already contains an @using BlazingPizza.Shared which matches the reusable components we have written.
When the OrderDetails component polls for order status updates, an update set of markers is returned with the latest location of the pizzas, which then gets reflected on the map.
The JavaScript interop code for the Map component was provided for you. Next you'll add some JavaScript interop code of your own.
It would be a shame if users accidentally deleted pizzas from their order (and ended up not buying them!). Let's add a confirm prompt when the user tries to delete a pizza. We'll show the confirm prompt using JavaScript interop.
Add a static JSRuntimeExtensions class to the Client project with a Confirm extension method off of IJSRuntime. Implement the Confirm method to call the built-in JavaScript confirm function. To do this, create a new class called JSRuntimeExtensions.cs in the Client Project root directory by right-clicking BlazingPizza.client, selecting Add, then New item, then Class. Replace it's contents with the following:
public static class JSRuntimeExtensions
{
public static ValueTask<bool> Confirm(this IJSRuntime jsRuntime, string message)
{
return jsRuntime.InvokeAsync<bool>("confirm", message);
}
}Open Index.razor in the client project's Pages folder and add the following two inject statements so that IJSRuntime service can be used there to make JavaScript interop calls.
@inject NavigationManager NavigationManager
@inject IJSRuntime JS
Add an async RemovePizza method to the @code block of Index.razor file that calls the Confirm method to verify if the user really wants to remove the pizza from the order.
async Task RemovePizza(Pizza configuredPizza)
{
if (await JS.Confirm($"Remove {configuredPizza.Special.Name} pizza from the order?"))
{
OrderState.RemoveConfiguredPizza(configuredPizza);
}
}
In the Index component update the event handler for the ConfiguredPizzaItems to call the new RemovePizza method.
@foreach (var configuredPizza in OrderState.Order.Pizzas)
{
<ConfiguredPizzaItem Pizza="configuredPizza" OnRemoved="@(() => RemovePizza(configuredPizza))" />
}
Run the app and try removing a pizza from the order.
Notice that we didn't have to update the signature of ConfiguredPizzaItem.OnRemoved to support async. This is another special property of EventCallback, it supports both synchronous event handlers and asynchronous event handlers.