BlazorParametersSet

This project is a minimal Blazor application created to test how Blazor handles component parameter updates, including:

• Primitive types
• Class (reference) types
• Record (immutable) types

The project demonstrates when OnParametersSet is called and how ShouldRender can be used to control whether a component actually re-renders — especially when dealing with complex parameter types.

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🔍 What This Project Demonstrates

1. Parent re-render behavior

The parent component (BlazorParametersSet) can trigger re-renders without changing any parameters. This lets you observe how often children get OnParametersSet calls even when nothing actually changed.

2. Primitive parameters

Blazor treats primitives (int, bool, string, etc.) as stable values.

• If the value stays the same, the child does not re-render.
• OnParametersSet is only invoked when the primitive value actually changes.

3. Class parameters

Blazor treats any reference type as “potentially changed,” so:

• OnParametersSet runs on every parent re-render, even if the same instance is passed.
• Without ShouldRender, the component always re-renders.

The project includes an updated component that uses a value snapshot + ShouldRender() to prevent unnecessary UI work.

4. Record parameters

Records behave like classes in Blazor regarding parameters — they always trigger OnParametersSet — but support value equality. Using ShouldRender() with record value comparison allows skipping re-renders when the record has not meaningfully changed.

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🧪 Components Included

PrimitiveChild

• Accepts an int.
• Shows that primitives only re-render when their value changes.

ClassChild

• Accepts ItemClass.
• Uses a snapshot to detect meaningful value changes.
• Uses ShouldRender() to avoid UI updates unless values changed.

RecordChild

• Accepts ItemRecord.
• Uses record value equality.
• ShouldRender() only returns true when the record value changes.

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🚀 How to Run

1. Clone or download the project.
2. Run it with:

   dotnet run
   

3. Navigate to:

/blazor-parameters-set

4. Use the buttons to:
   • Re-render the parent without changing parameters
   • Mutate class instance properties
   • Replace class/record with the same or different values
   • Observe:
     • OnParametersSet calls
     • Actual renders (from ShouldRender)
     • Console logs

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📈 Why This Project Exists

There's a common misconception that:

• Blazor only re-renders children when parameters change
• Or that records behave differently than classes regarding render triggering

This project proves the actual rules:

✔ OnParametersSet runs for complex types on every parent render

✔ Primitives only trigger updates when the value changes

✔ Records don’t affect Blazor’s parameter pipeline, but help with value comparison

✔ ShouldRender() is the only way to control UI-level rendering for complex params

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📁 Project Structure

BlazorParametersSet/
  ├── Pages/
  │     └── BlazorParametersSet.razor
  ├── Components/
  │     ├── PrimitiveChild.razor
  │     ├── ClassChild.razor
  │     └── RecordChild.razor
  ├── Models/
  │     ├── ItemClass.cs
  │     └── ItemRecord.cs
  ├── README.md
  └── Program.cs

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📬 Notes

This project is purely educational and meant for testing Blazor parameter behavior in an isolated environment.
Feel free to expand it with:

• Cascading values
• RenderFragment tests
• Event-driven updates
• Diffing experiments

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📦 Download

The full project archive is included in this release.