title
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19:620
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</InputRadioGroup>
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19:621
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19:622
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Finally, Blazor also offers an InputFile component together with all the tools for processing and uploading the file. We will not cover this here, but the Further reading section contains links to the official documentation.
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19:623
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The next section describes Blazor tools for modifying the host page <head> tag.
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19:624
|
Modifying HTML <head> content from Blazor components
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19:625
|
Since the whole component tree is placed inside the body of the index.html host page, the components markup has no direct access to the index.html host page <head> tag. Modifying the content of the <head> tag is necessary when the developer would like to adapt the title shown in the browser tab to the actual Blazor page that is being displayed. In fact, this title is contained within the <head> tag:
|
19:626
|
<head>
|
19:627
|
<title>This is the title shown in the browser tab</title>
|
19:628
|
...
|
19:629
|
</head>
|
19:630
| |
19:631
|
For this reason, the .NET 6 version of Blazor introduced specific constructs for modifying the host page <head> tag from inside Blazor components.
|
19:632
|
First of all, we must inform the Blazor application about how to reach the <head> tag content. This is done in Program.cs with the same technique used to specify the Blazor application root:
|
19:633
|
var builder = WebAssemblyHostBuilder.CreateDefault(args);
|
19:634
|
builder.RootComponents.Add<App>(`#app`);
|
19:635
|
// The line below adds support for modifying
|
19:636
|
// the <head> tag content
|
19:637
|
builder.RootComponents.Add<HeadOutlet>(`head::after`);
|
19:638
|
...
|
19:639
| |
19:640
|
After that, each component can replace the HTML title by specifying the new string inside a PageTitle component instance:
|
19:641
|
<PageTitle>This string replaces the page title</PageTitle>
|
19:642
| |
19:643
|
Moreover, each component can append other HTML content to the <head> tag by placing it inside a HeadContent instance:
|
19:644
|
<HeadContent>
|
19:645
|
<meta name=`description` content=`This is a page description`>
|
19:646
|
</HeadContent>
|
19:647
| |
19:648
|
In this section, you learned all that is needed to write a simple Blazor application that doesn’t exchange data with a server. The next section analyzes some advanced features and will enable you to interact with a server to handle authentication, authorization, and more.
|
19:649
|
Blazor advanced features
|
19:650
|
This section provides short descriptions of various Blazor advanced features organized into subsections:
|
19:651
| |
19:652
|
References to components and HTML elements
|
19:653
|
JavaScript interoperability
|
19:654
|
Globalization and localization
|
19:655
|
Authentication and authorization
|
19:656
|
Communication with the server
|
19:657
|
AOT compilation
|
19:658
| |
19:659
|
Because of a lack of space, we can’t give all the details of each feature, but the details are covered by links in the Further reading section. We start with how to reference components and HTML elements defined in Razor markup.
|
19:660
|
References to components and HTML elements
|
19:661
|
Sometimes, we might need a reference to a component in order to call some of its methods. This is the case, for instance, for a component that implements a modal window:
|
19:662
|
<Modal @ref=`myModal`>
|
19:663
|
...
|
19:664
|
</Modal>
|
19:665
|
...
|
19:666
|
<button type=`button` class=`btn btn-primary`
|
19:667
|
@onclick=`() => myModal.Show()`>
|
19:668
|
Open modal
|
19:669
|
</button>
|
19:670
|
...
|
19:671
|
@code{
|
19:672
|
private Modal myModal {get; set;}
|
19:673
|
...
|
19:674
|
}
|
19:675
| |
19:676
|
As the preceding example shows, references are captured with the @ref directive. The same @ref directive can also be used to capture references to HTML elements. HTML references have an ElementReference type and are typically used to call JavaScript functions on HTML elements, as explained in the next subsection.
|
19:677
|
JavaScript interoperability
|
19:678
|
Since Blazor doesn’t expose all JavaScript features to C# code, and since it is convenient to take advantage of the huge JavaScript code base, sometimes it is necessary to invoke JavaScript functions. Blazor allows this through the IJSRuntime interface that can be injected into a component via dependency injection.
|
19:679
|
Once we have an IJSRuntime instance, a JavaScript function that returns a value can be called as shown here:
|
19:680
|
T result = await jsRuntime.InvokeAsync<T>(
|
19:681
|
`<name of JavaScript function or method>`, arg1, arg2....);
|
19:682
| |
19:683
|
Functions that do not return any argument can be invoked as shown here:
|
19:684
|
await jsRuntime.InvokeAsync(
|
19:685
|
`<name of JavaScript function or method>`, arg1, arg2....);
|
19:686
| |
19:687
|
Arguments can be either basic types or objects that can be serialized in JSON, while the name of the JavaScript function is a string that can contain dots that represent access to properties, sub-properties, and method names, such as the `myJavaScriptObject.myProperty.myMethod` string.
|
19:688
|
Thus, for instance, we can save a string in the browser’s local storage with the following code:
|
19:689
|
await jsRuntime
|
19:690
|
.InvokeVoidAsync(`window.localStorage.setItem`,
|
19:691
|
myLocalStorageKey, myStringToSave);
|
19:692
| |
19:693
|
Arguments can also be ElementReference instances captured with the @ref directive, in which case they are received as HTML elements on the JavaScript side.
|
19:694
|
The JavaScript functions invoked must be defined either in the Index.html file or in JavaScript files referenced in Index.html.
|
19:695
|
If you are writing a component library with a Razor library project, JavaScript files can be embedded together with CSS files as resources in the DLL library. You just need to add a wwwroot folder in the project root and place the needed CSS and JavaScript files in that folder or some subfolder of it. After that, these files can be referenced as follows:
|
19:696
|
_content/<dll name>/<file path relative to wwwroot>
|
19:697
| |
19:698
|
Accordingly, if the filename is myJsFile.js, the DLL name is MyCompany.MyLibrary, and the file is placed in the js folder inside wwwroot, then its reference will be:
|
19:699
|
_content/MyCompany.MyLibrary/js/myJsFile.js
|
19:700
| |
19:701
|
It is worth pointing out that all CSS files added to components (CSS isolation) we mentioned earlier in this chapter are compiled into a unique CSS file that is added as a DLL resource. This file must be referenced in the index.html page as:
|
19:702
|
<assembly name>.Client.styles.css
|
19:703
| |
19:704
|
If your JavaScript files are organized as ES6 modules, you can avoid referencing them in Index.html and can load the modules directly, as shown here:
|
19:705
|
// _content/MyCompany.MyLibrary/js/myJsFile.js JavaScript file
|
19:706
|
export function myFunction ()
|
19:707
|
{
|
19:708
|
...
|
19:709
|
}
|
19:710
|
...
|
19:711
|
//C# code
|
19:712
|
var module = await jsRuntime.InvokeAsync<JSObjectReference>(
|
19:713
|
`import`, `./_content/MyCompany.MyLibrary/js/myJsFile.js`);
|
19:714
|
...
|
19:715
|
T res= await module.InvokeAsync<T>(`myFunction`)
|
19:716
| |
19:717
|
In addition, instance methods of C# objects can be called from JavaScript code, by taking the following steps:
|
19:718
| |
19:719
|
Say the C# method is called MyMethod. Decorate the MyMethod method with the [JSInvokable] attribute.
|
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