# Skill 13 - Blazor Components

## Core Concepts

- Blazor apps are built from components.
- Components combine markup, C# code, parameters, events, lifecycle methods, and rendering behavior.
- Rendering can happen server-side, client-side, or with static server-side rendering depending on hosting model.

## Component Rules

- Keep components small and focused.
- Use parameters for input and event callbacks for output.
- Avoid putting complex business logic directly in components.
- Extract reusable UI into child components.
- Use services for data access and state that crosses components.
- Be explicit about render modes and interactivity.

## Lifecycle Rules

- Use initialization lifecycle methods for loading setup data.
- Use parameter-set lifecycle methods when behavior depends on changing parameters.
- Avoid unnecessary calls to `StateHasChanged`.
- Dispose subscriptions and unmanaged resources.

## Forms

- Use `EditForm` for model binding and validation.
- Use validation attributes or custom validators for input rules.
- Keep validation rules shared with the domain when practical.
- Do not trust client-side validation alone.

## Performance

- Avoid excessive component re-rendering.
- Use `@key` when rendering lists whose identity matters.
- Keep large data operations out of the render path.