.NET MAUI 9 to 10 upgrade instructions

[PureWeen]

Pull Request Checklist

• I have read and followed the CONTRIBUTING.md guidelines.
• My contribution adds a new instruction, prompt, or chat mode file in the correct directory.
• The file follows the required naming convention.
• The content is clearly structured and follows the example format.
• I have tested my instructions, prompt, or chat mode with GitHub Copilot.
• I have run npm start and verified that README.md is up to date.

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Description

Comprehensive upgrade instructions for migrating .NET MAUI applications from version 9 to version 10.

What This Does

Guides developers through the .NET MAUI 9 → 10 upgrade process, covering:

• Breaking changes: MessagingCenter (now internal), ListView/TableView deprecation
• Deprecated APIs: Animation methods, DisplayAlert, IsBusy
• Migration strategies: Step-by-step ListView → CollectionView conversion with examples
• Troubleshooting: Common issues and solutions
• Automation tools: Scripts for bulk updates

Usage

Ask GitHub Copilot:

"Upgrade my .NET MAUI project from .NET 9 to .NET 10 following the upgrade instructions"

Context

• Prioritized by severity (P0 = must fix, P1 = deprecated, P2 = recommended)
• Includes before/after code examples for all changes
• Covers the most complex migration (ListView → CollectionView) in detail
• Provides realistic time estimates (4-8 hours for simple apps, 2-5 days for complex)

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Type of Contribution

• New instruction file.
• New prompt file.
• New chat mode file.
• New collection file.
• Update to existing instruction, prompt, chat mode, or collection.
• Other (please specify):

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By submitting this pull request, I confirm that my contribution abides by the Code of Conduct and will be licensed under the MIT License.

[Copilot]

Pull Request Overview

This PR adds comprehensive upgrade instructions for migrating .NET MAUI applications from version 9 to version 10. The guide covers breaking changes (MessagingCenter, ListView/TableView deprecation), deprecated APIs (animation methods, DisplayAlert, IsBusy), migration strategies with detailed examples, troubleshooting guidance, and automation tools for bulk updates.

Key changes:

• Detailed step-by-step migration guide with priority-based organization (P0/P1/P2)
• Extensive ListView to CollectionView conversion examples with before/after code
• MessagingCenter to WeakReferenceMessenger migration with behavioral differences highlighted
• Bulk migration tools including regex patterns and PowerShell scripts

Reviewed Changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 1 comment.

File	Description
instructions/dotnet-maui-9-to-dotnet-maui-10-upgrade.instructions.md	New comprehensive 1595-line upgrade guide covering all breaking changes and deprecated APIs for .NET MAUI 9→10 migration
docs/README.instructions.md	Added entry in the instructions index table with installation links