Tag: blazor

Synchronous IDisposable

@implements IDisposable

...

@code {
    ...

    public void Dispose()
    {
        obj?.Dispose();
    }
}

Asynchronous IAsyncDisposable

@implements IAsyncDisposable

...

@code {
    ...

    public async ValueTask DisposeAsync()
    {
        if (obj is not null)
        {
            await obj.DisposeAsync();
        }
    }
}

Event handlers

Always unsubscribe event handlers from .NET events.

@implements IDisposable

<EditForm EditContext="@editContext">
    ...
    <button type="submit" disabled="@formInvalid">Submit</button>
</EditForm>

@code {
    ...

    private EventHandler<FieldChangedEventArgs>? fieldChanged;

    protected override void OnInitialized()
    {
        editContext = new(model);

        fieldChanged = (_, __) =>
        {
            ...
        };

        editContext.OnFieldChanged += fieldChanged;
    }

    public void Dispose()
    {
        editContext.OnFieldChanged -= fieldChanged;
    }
}

References
https://docs.microsoft.com/en-us/aspnet/core/blazor/components/lifecycle?view=aspnetcore-6.0#synchronous-idisposable
https://docs.microsoft.com/en-us/aspnet/core/blazor/components/lifecycle?view=aspnetcore-6.0#asynchronous-iasyncdisposable
https://docs.microsoft.com/en-us/aspnet/core/blazor/components/lifecycle?view=aspnetcore-6.0#event-handlers
https://www.syncfusion.com/faq/blazor/components/how-can-i-properly-dispose-a-component-in-blazor

dotnet add package BlazorPro.BlazorSize 

Add a reference to the namespace in your _Imports.razor or at the top of a page.

@using BlazorPro.BlazorSize

In startup.cs register ResizeListener with the applications service collection.

services.AddMediaQueryService();

Add the MediaQueryList

Add a MediaQueryList to your application’s main layout or root. The MediaQueryList is responsible for communicating with all MediaQuery components in your app. The MediaQueryList component will consolidate redundant media queries and manage resources so that unused event listeners are disposed of properly.

<MediaQueryList>
    <div class="sidebar">
        <NavMenu />
    </div>

    <div class="main">
        <div class="top-row px-4">
            <a href="http://blazor.net" target="_blank" class="ml-md-auto">About</a>
        </div>

        <div class="content px-4">
            @Body
        </div>
    </div>
</MediaQueryList>

Add a MediaQuery and bind

Using the @bind-Matches directive we can easily bind to a browser’s media query and respond to it.

@if (IsSmall)
{
    <WeatherCards Data="forecasts"></WeatherCards>
}
else
{
    <WeatherGrid Data="forecasts"></WeatherGrid>
}

@if (IsMedium)
{
    <span>Medium</span>
}

<MediaQuery Media="@Breakpoints.OnlyMedium" @bind-Matches="IsMedium" />
<MediaQuery Media="@Breakpoints.SmallDown" @bind-Matches="IsSmall" />

@code {
    WeatherForecast[] forecasts;

    bool IsMedium = false;
    bool IsSmall = false;

    protected override async Task OnInitializedAsync()
    {
        forecasts = await Http.GetFromJsonAsync<WeatherForecast[]>("sample-data/weather.json");
    }
}

No-Code Templates

The MediaQuery component can also use templates instead of the @bind directive. Templates are useful for swapping out UI bits when the screen size changes.

<MediaQuery Media="@Breakpoints.SmallDown">
    <Matched>
        <WeatherCards Data="forecasts"></WeatherCards>
    </Matched>
    <Unmatched>
        <WeatherGrid Data="forecasts"></WeatherGrid>
    </Unmatched>
</MediaQuery>

Helpers

Common media queries are already included as helpers to keep you out of the Bootstrap docs. Stay in your code longer and write cleaner statements too!

/// @media(min-width: 576px) { ... }
/// Small devices (landscape phones, 576px and up)
IsSmallUpMedia = await listener.MatchMedia(Breakpoints.SmallUp);

/// @media(min-width: 768px) { ... }
/// Medium devices (tablets, 768px and up)
IsMediumUpMedia = await listener.MatchMedia(Breakpoints.MediumUp);

// Large devices (desktops, 992px and up)
/// @media(min-width: 992px) { ... }
IsLargeUpMedia = await listener.MatchMedia(Breakpoints.LargeUp);

/// Extra large devices (large desktops, 1200px and up)
/// @media(min-width: 1200px) { ... }
IsXLargeUpMedia = await listener.MatchMedia(Breakpoints.XLargeUp);

/// Extra small devices (portrait phones, less than 576px)
/// @media(max-width: 575.98px) { ... }
IsXSmallDown = await listener.MatchMedia(Breakpoints.XSmallDown);

/// Small devices (landscape phones, less than 768px)
/// @media(max-width: 767.98px) { ... }
IsSmallDown = = await listener.MatchMedia(Breakpoints.SmallDown);

/// Medium devices (tablets, less than 992px)
/// @media(max-width: 991.98px) { ... }
IsMediumDown = = await listener.MatchMedia(Breakpoints.MediumDown);

/// Large devices (desktops, less than 1200px)
/// @media(max-width: 1199.98px) { ... }
LargeDown = = await listener.MatchMedia(Breakpoints.LargeDown);

/// Small devices (landscape phones, 576px and up)
/// @media(min-width: 576px) and(max-width: 767.98px) { ... }
IsSmallOnly = = await listener.MatchMedia(Breakpoints.OnlySmall);

/// Medium devices (tablets, 768px and up)
/// @media(min-width: 768px) and(max-width: 991.98px) { ... }
IsMediumOnly = = await listener.MatchMedia(Breakpoints.OnlyMedium);

/// Large devices (desktops, 992px and up)
/// @media(min-width: 992px) and(max-width: 1199.98px) { ... }
IsOnlyLarge = = await listener.MatchMedia(Breakpoints.OnlyLarge);

/// <summary>
/// Combines two media queries with the `and` keyword.
/// Values must include parenthesis.
/// Ex: (min-width: 992px) and (max-width: 1199.98px)
Breakpoints.Between(string min, string max)

Example:
string BetweenMediumAndLargeOnly => Breakpoints.Between(Breakpoints.MediumUp, Breakpoints.LargeDown);
// out: "(min-width: 768px) and (max-width: 1199.98px)"

IsBetweenMediumAndLargeOnly = await listener.MatchMedia(BetweenMediumAndLargeOnly);

Listening for the Resize event

The ResizeListener is a service that allows your application to listen for the browser’s resize event. The ResizeListener is a throttled to improve performance and can be adjusted thru configuration. If you only need to respond the user’s device or screen size the MediaQueryList & MediaQuery components provide a more performant experience.

Configure DI

In startup.cs register ResizeListener with the applications service collection.

services.AddScoped<ResizeListener>();
//services.AddResizeListener(options =>
//                            {
//                                options.ReportRate = 300;
//                                options.EnableLogging = true;
//                                options.SuppressInitEvent = true;
//                            });

Usage

This example shows how to get the browsers width/height and check for media query matches. Depending on the matched media query the view can toggle between two components WeatherGrid or WeatherCards.

@inject IResizeListener listener
@implements IDisposable
@page "/fetchdata"

@using BlazorSize.Example.Data
@inject WeatherForecastService ForecastService

<h1>Weather forecast</h1>

<p>This component demonstrates adaptive rendering of a Blazor UI.</p>

<h3>Height: @browser.Height</h3>
<h3>Width: @browser.Width</h3>
<h3>MQ: @IsSmallMedia</h3>

@if (IsSmallMedia)
{
    
    <WeatherCards Data="forecasts"></WeatherCards>
}
else
{
    
    <WeatherGrid Data="forecasts"></WeatherGrid>
}

@code {
    WeatherForecast[] forecasts;

    // We can also capture the browser's width / height if needed. We hold the value here.
    BrowserWindowSize browser = new BrowserWindowSize();

    bool IsSmallMedia = false;

    protected override async Task OnInitializedAsync()
    {
        forecasts = await ForecastService.GetForecastAsync(DateTime.Now);
    }

    protected override void OnAfterRender(bool firstRender)
    {

        if (firstRender)
        {
            // Subscribe to the OnResized event. This will do work when the browser is resized.
            listener.OnResized += WindowResized;
        }
    }

    void IDisposable.Dispose()
    {
        // Always use IDisposable in your component to unsubscribe from the event.
        // Be a good citizen and leave things how you found them. 
        // This way event handlers aren't called when nobody is listening.
        listener.OnResized -= WindowResized;
    }

    // This method will be called when the window resizes.
    // It is ONLY called when the user stops dragging the window's edge. (It is already throttled to protect your app from perf. nightmares)
    async void WindowResized(object _, BrowserWindowSize window)
    {
        // Get the browsers's width / height
        browser = window;

        // Check a media query to see if it was matched. We can do this at any time, but it's best to check on each resize
        IsSmallMedia = await listener.MatchMedia(Breakpoints.SmallDown);

        // We're outside of the component's lifecycle, be sure to let it know it has to re-render.
        StateHasChanged();
    }

}

References
https://www.nuget.org/packages/BlazorPro.BlazorSize

If the app is required to check authorization rules as part of procedural logic, use a cascaded parameter of type Task<AuthenticationState> to obtain the user’s ClaimsPrincipal. Task<AuthenticationState> can be combined with other services, such as IAuthorizationService, to evaluate policies.

@using Microsoft.AspNetCore.Authorization
@inject IAuthorizationService AuthorizationService

<button @onclick="@DoSomething">Do something important</button>

@code {
    [CascadingParameter]
    private Task<AuthenticationState> authenticationStateTask { get; set; }

    private async Task DoSomething()
    {
        var user = (await authenticationStateTask).User;

        if (user.Identity.IsAuthenticated)
        {
            // Perform an action only available to authenticated (signed-in) users.
        }

        if (user.IsInRole("admin"))
        {
            // Perform an action only available to users in the 'admin' role.
        }

        if ((await AuthorizationService.AuthorizeAsync(user, "content-editor"))
            .Succeeded)
        {
            // Perform an action only available to users satisfying the 
            // 'content-editor' policy.
        }
    }
}

References
https://docs.microsoft.com/en-us/aspnet/core/blazor/security/?view=aspnetcore-6.0#procedural-logic

The Router component, in conjunction with the AuthorizeRouteView component, allows the app to specify custom content if:

• The user fails an [Authorize] condition applied to the component. The markup of the <NotAuthorized> element is displayed. The [Authorize] attribute is covered in the [Authorize] attribute section.
• Asynchronous authorization is in progress, which usually means that the process of authenticating the user is in progress. The markup of the <Authorizing> element is displayed.
• Content isn’t found. The markup of the <NotFound> element is displayed.

<CascadingAuthenticationState>
    <Router AppAssembly="@typeof(Program).Assembly">
        <Found Context="routeData">
            <AuthorizeRouteView RouteData="@routeData" 
                DefaultLayout="@typeof(MainLayout)">
                <NotAuthorized>
                    <h1>Sorry</h1>
                    <p>You're not authorized to reach this page.</p>
                    <p>You may need to log in as a different user.</p>
                </NotAuthorized>
                <Authorizing>
                    <h1>Authorization in progress</h1>
                    <p>Only visible while authorization is in progress.</p>
                </Authorizing>
            </AuthorizeRouteView>
        </Found>
        <NotFound>
            <LayoutView Layout="@typeof(MainLayout)">
                <h1>Sorry</h1>
                <p>Sorry, there's nothing at this address.</p>
            </LayoutView>
        </NotFound>
    </Router>
</CascadingAuthenticationState>

References
https://docs.microsoft.com/en-us/aspnet/core/blazor/security/?view=aspnetcore-6.0#customize-unauthorized-content-with-the-router-component

The [Authorize] attribute can be used in Razor components:

@page "/"
@attribute [Authorize]

You can only see this if you're signed in.

Only use [Authorize] on @page components reached via the Blazor Router. Authorization is only performed as an aspect of routing and not for child components rendered within a page. To authorize the display of specific parts within a page, use AuthorizeView instead.

The [Authorize] attribute also supports role-based or policy-based authorization. For role-based authorization, use the Roles parameter:

@page "/"
@attribute [Authorize(Roles = "admin, superuser")]

<p>You can only see this if you're in the 'admin' or 'superuser' role.</p>

For policy-based authorization, use the Policy parameter:

@page "/"
@attribute [Authorize(Policy = "content-editor")]

<p>You can only see this if you satisfy the 'content-editor' policy.</p>

If neither Roles nor Policy is specified, [Authorize] uses the default policy, which by default is to treat:

• Authenticated (signed-in) users as authorized.
• Unauthenticated (signed-out) users as unauthorized.

Refererences
https://docs.microsoft.com/en-us/aspnet/core/blazor/security/?view=aspnetcore-6.0#authorize-attribute

<AuthorizeView>
    <Authorized>
        <h1>Hello, @context.User.Identity.Name!</h1>
        <p>You can only see this content if you're authenticated.</p>
    </Authorized>
    <Authorizing>
        <h1>Authentication in progress</h1>
        <p>You can only see this content while authentication is in progress.</p>
    </Authorizing>
</AuthorizeView>

This approach isn’t normally applicable to Blazor Server apps. Blazor Server apps know the authentication state as soon as the state is established. Authorizing content can be provided in a Blazor Server app’s AuthorizeView component, but the content is never displayed.

References
https://docs.microsoft.com/en-us/aspnet/core/blazor/security/?view=aspnetcore-6.0#content-displayed-during-asynchronous-authentication

The AuthorizeView component supports role-based or policy-based authorization.

For role-based authorization, use the Roles parameter:

<AuthorizeView Roles="admin, superuser">
    <p>You can only see this if you're an admin or superuser.</p>
</AuthorizeView>

For policy-based authorization, use the Policy parameter:

<AuthorizeView Policy="content-editor">
    <p>You can only see this if you satisfy the "content-editor" policy.</p>
</AuthorizeView>

References
https://docs.microsoft.com/en-us/aspnet/core/blazor/security/?view=aspnetcore-6.0#role-based-and-policy-based-authorization

The AuthorizeView component selectively displays UI content depending on whether the user is authorized. This approach is useful when you only need to display data for the user and don’t need to use the user’s identity in procedural logic.

The component exposes a context variable of type AuthenticationState, which you can use to access information about the signed-in user:

<AuthorizeView>
    <h1>Hello, @context.User.Identity.Name!</h1>
    <p>You can only see this content if you're authenticated.</p>
</AuthorizeView>

You can also supply different content for display if the user isn’t authorized:

<AuthorizeView>
    <Authorized>
        <h1>Hello, @context.User.Identity.Name!</h1>
        <p>You can only see this content if you're authorized.</p>
        <button @onclick="SecureMethod">Authorized Only Button</button>
    </Authorized>
    <NotAuthorized>
        <h1>Authentication Failure!</h1>
        <p>You're not signed in.</p>
    </NotAuthorized>
</AuthorizeView>

@code {
    private void SecureMethod() { ... }
}

References
https://docs.microsoft.com/en-us/aspnet/core/blazor/security/?view=aspnetcore-6.0#authorizeview-component

@page "/"

<button @onclick="LogUsername">Log username</button>

<p>@authMessage</p>

@code {
    [CascadingParameter]
    private Task<AuthenticationState> authenticationStateTask { get; set; }

    private string authMessage;

    private async Task LogUsername()
    {
        var authState = await authenticationStateTask;
        var user = authState.User;

        if (user.Identity.IsAuthenticated)
        {
            authMessage = $"{user.Identity.Name} is authenticated.";
        }
        else
        {
            authMessage = "The user is NOT authenticated.";
        }
    }
}

Set up the Task<AuthenticationState> cascading parameter using the AuthorizeRouteView and CascadingAuthenticationState components in the App component (App.razor):

<CascadingAuthenticationState>
    <Router AppAssembly="@typeof(Program).Assembly">
        <Found Context="routeData">
            <AuthorizeRouteView RouteData="@routeData" 
                DefaultLayout="@typeof(MainLayout)" />
        </Found>
        <NotFound>
            <LayoutView Layout="@typeof(MainLayout)">
                <p>Sorry, there's nothing at this address.</p>
            </LayoutView>
        </NotFound>
    </Router>
</CascadingAuthenticationState>

In a Blazor WebAssembly App, add services for options and authorization to Program.cs:

builder.Services.AddOptions();
builder.Services.AddAuthorizationCore();

In a Blazor Server app, services for options and authorization are already present, so no further action is required.

References
https://docs.microsoft.com/en-us/aspnet/core/blazor/security/?view=aspnetcore-6.0#expose-the-authentication-state-as-a-cascading-parameter