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March 03, 2025 01:05
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Blazor Cheat Sheet

A quick reference guide for Blazor, covering components, data binding, routing, and other essential concepts for building interactive web UIs with C#.

Component Basics

Component Definition

Blazor components are reusable UI elements written in C# and HTML (Razor syntax).

Example:

// MyComponent.razor
<h1>Hello, @Name</h1>

@code {
    [Parameter]
    public string? Name { get; set; }
}

Components can receive data through parameters.

Use the [Parameter] attribute to define component parameters.

Lifecycle Methods

OnInitialized

Called when the component is initialized, after parameters are set.

OnParametersSet

Called after the component receives parameters from its parent.

OnAfterRender / OnAfterRenderAsync

Called after the component has been rendered. Use firstRender parameter to run logic only on the initial render.

ShouldRender

Allows you to control when a component should re-render. Return true to re-render, false to skip.

IDisposable.Dispose

Called when the component is being disposed. Use this to unsubscribe from events and release resources.

Event Handling

Blazor uses standard C# event handling.

Example:

<button @onclick="HandleClick">Click me</button>

@code {
    private void HandleClick()
    {
        Console.WriteLine("Button clicked!");
    }
}

Use @onclick, @onchange, @oninput, etc. to bind events to C# methods.

Data Binding

One-Way Binding

Displaying data from a C# variable in the UI.

Example:

<p>Current count: @currentCount</p>

@code {
    private int currentCount = 0;
}

Two-Way Binding

Allows updating a C# variable when the UI element changes.

Example:

<input type="text" @bind="inputValue" />
<p>You typed: @inputValue</p>

@code {
    private string? inputValue;
}

@bind attribute provides two-way binding. Use @bind:event to specify the event that triggers the update.

Binding with different event 

<input type="text" @bind="inputValue" @bind:event="oninput" />
<p>You typed: @inputValue</p>

@code {
    private string? inputValue;
}

Routing

Page Directive

Defines the route for a component, making it accessible via a URL.

Example:

@page "/counter"

<h1>Counter</h1>

Use @page directive at the top of the component file to specify the route.

Route Parameters

Pass data to a component through the URL.

Example:

@page "/user/{Id:int}"

<h1>User Details</h1>
<p>User ID: @Id</p>

@code {
    [Parameter]
    public int Id { get; set; }
}

Use {parameterName:dataType} syntax to define route parameters. The type constraint ensures that the parameter matches the expected type.

Navigation

Programmatically navigate between pages using NavigationManager.

Example:

@inject NavigationManager NavigationManager

<button @onclick="Navigate">Go to Counter</button>

@code {
    private void Navigate()
    {
        NavigationManager.NavigateTo("/counter");
    }
}

Inject NavigationManager into your component to use its NavigateTo method.

Dependency Injection

Service Registration

Register services in Program.cs for use in Blazor components.

Example:

builder.Services.AddScoped<IMyService, MyService>();

Use AddScoped, AddTransient, or AddSingleton to register services with different lifetimes.

Service Injection

Inject services into components using the @inject directive.

Example:

@inject IMyService MyService

<h1>Data from Service</h1>
<p>@MyService.GetData()</p>

Use @inject followed by the service type and a variable name to access the service.