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Blazor MCQ questions

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Blazor tutorial Interview questions

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Blazor practice testMultiple choice Question 1 of 10

How does a child notify its parent?

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All questions with answers

Which file extension do Blazor components use?
- A.cshtml
- B.razor
- C.blazor
- D.cs only
Show answer
Answer: B. .razor
.cshtml is for MVC views and Razor Pages.
Which directive makes a component routable?
- A@route
- B@page
- C@url
- D@path
Show answer
Answer: B. @page
@page "/counter" maps the URL to the component.
Which attribute marks a component parameter?
- A[Input]
- B[Parameter]
- C[Prop]
- D[Bind]
Show answer
Answer: B. [Parameter]
Parameters must be public properties.
Which syntax handles a button click?
- Aonclick="Save()"
- B@onclick="Save"
- C(click)="Save()"
- Dv-on:click="Save"
Show answer
Answer: B. @onclick="Save"
Blazor event attributes start with @.
Which render mode runs .NET in the browser?
- AStatic SSR
- BInteractiveServer
- CInteractiveWebAssembly
- DPrerendered
Show answer
Answer: C. InteractiveWebAssembly
The runtime is downloaded and executed via WebAssembly.
What transport does Interactive Server use?
- ALong polling only
- BA SignalR connection (WebSockets when available)
- CgRPC
- DServer-Sent Events only
Show answer
Answer: B. A SignalR connection (WebSockets when available)
UI events and DOM diffs travel over the circuit.
Which directive sets the render mode on a component?
- A@mode
- B@rendermode
- C@interactive
- D@render
Show answer
Answer: B. @rendermode
For example @rendermode InteractiveServer.
Which component renders a form with validation support?
- A<form>
- B<EditForm>
- C<FormView>
- D<InputForm>
Show answer
Answer: B. <EditForm>
EditForm creates an EditContext for the model.
Which component enables Data Annotations validation inside EditForm?
- A<Validator />
- B<DataAnnotationsValidator />
- C<ValidationSummary /> alone
- D<ModelValidator />
Show answer
Answer: B. <DataAnnotationsValidator />
ValidationSummary and ValidationMessage then display the errors.
Which method should a component call to re-render after an external event?
- ARefresh()
- BStateHasChanged()
- CRender()
- DUpdate()
Show answer
Answer: B. StateHasChanged()
Use InvokeAsync(StateHasChanged) when called from another thread.
Which lifecycle method runs once when the component is first initialised?
- AOnParametersSet
- BOnInitializedAsync
- COnAfterRender
- DDispose
Show answer
Answer: B. OnInitializedAsync
It may run twice when prerendering is enabled.
How does a child notify its parent?
- AA static event
- BAn EventCallback parameter
- CChanging the parent’s field
- DJavaScript interop
Show answer
Answer: B. An EventCallback parameter
The parent passes a handler and the child calls InvokeAsync.
Which component shares a value with all descendants?
- A<CascadingValue>
- B<Provider>
- C<Context>
- D<Shared>
Show answer
Answer: A. <CascadingValue>
Descendants receive it with [CascadingParameter].
Which interface calls JavaScript from C#?
- AIJSRuntime
- BIJavaScript
- CIBrowser
- DIJsInterop
Show answer
Answer: A. IJSRuntime
await JS.InvokeVoidAsync("alert", "Hi").
When is JS interop safe in an Interactive Server component?
- AIn the constructor
- BIn OnInitialized during prerendering
- CIn OnAfterRenderAsync
- DAnywhere
Show answer
Answer: C. In OnAfterRenderAsync
During prerendering there is no browser connection yet.
Which component shows UI only to authenticated users?
- A<Authorize>
- B<AuthorizeView>
- C<SecureView>
- D<UserOnly>
Show answer
Answer: B. <AuthorizeView>
It renders Authorized or NotAuthorized content.
Why does this list flicker and lose input focus on update?
Razor / Markup Illustrative
```
1@foreach (var item in Items)
2{
3    <TodoRow Item="item" />
4}
```
- ANothing is wrong
- BItems have no @key, so Blazor cannot match elements to data
- C@foreach is not allowed
- DInputs cannot be in lists
Show answer
Answer: B. Items have no @key, so Blazor cannot match elements to data
Add @key="item.Id" so elements are preserved.
Which service creates short-lived DbContexts for components?
- ADbContextPool
- BIDbContextFactory<T>
- CIServiceProvider only
- DDbContextScope
Show answer
Answer: B. IDbContextFactory<T>
Create one per operation with CreateDbContextAsync.
Which component catches rendering exceptions in part of the UI?
- A<ErrorBoundary>
- B<TryCatch>
- C<Fallback>
- D<SafeView>
Show answer
Answer: A. <ErrorBoundary>
It shows ErrorContent instead of crashing the whole app.
Which component virtualises long lists?
- A<Virtualize>
- B<LazyList>
- C<InfiniteList>
- D<Paged>
Show answer
Answer: A. <Virtualize>
Only visible rows are rendered.
Which render mode keeps a SignalR connection open?
- AStatic SSR
- BInteractive Server
- CInteractive WebAssembly
- DNone
Show answer
Answer: B. Interactive Server
Interactive Server handles UI events on the server over a SignalR connection.
From the lesson: Blazor Web App
Interactive Auto uses WebAssembly for the very first visit.
- ATrue
- BFalse
Show answer
Answer: B. False
Auto uses Interactive Server first, then WebAssembly once the runtime has been downloaded and cached.
From the lesson: Blazor Web App
What file extension do Blazor components use?
- A.cshtml
- B.razor
- C.blazor
- D.cs only
Show answer
Answer: B. .razor
Components are .razor files.
From the lesson: Introduction to Blazor
In a Blazor Web App, every page is interactive by default.
- ATrue
- BFalse
Show answer
Answer: B. False
Pages use static server rendering unless an interactive render mode is applied.
From the lesson: Introduction to Blazor
Over what does Interactive Server send UI updates?
- AWebAssembly
- BA SignalR connection (circuit)
- CServer-sent HTML pages
- DService workers
Show answer
Answer: B. A SignalR connection (circuit)
Interactive Server keeps a SignalR circuit per user.
From the lesson: Blazor Architecture