maui collectionview-ios.instructions.md

Coding guidance for .NET MAUI CollectionView on iPhone, iPad, Mac, and Mac Catalyst. CollectionView displays a scrolling list or grid of items using Apple's UICollectionView underneath.

In plain words
What is it for?
Use it when changing CollectionView handlers, cells, item layouts, headers or footers, measurement, invalidation, or event cleanup on Apple platforms.
Why use it?
It helps avoid incorrect item sizes, visual glitches, stale layout settings, memory leaks, and unnecessarily expensive updates.

Instructions file for GitHub Copilot

Install

Getting it into your agent

One page per mod, every tool's command on it. A separate URL per tool would split the same page into five that compete with each other.

agentmods
npx agentmods add instructions/dotnet/maui/collectionview-ios
Clone the repo
git clone --depth 1 https://github.com/dotnet/maui

Made for: GitHub Copilot.

Per session 460 This file is loaded in full into every session.
When invoked 460 The same file — it is already loaded in full.
Security scan A 0 findings. Scan, not verified.
Origin original No closer match found in the catalogue.
Token cost

What it costs to keep this loaded

Counted locally with the o200k_base tokenizer, which is exact for GPT models; Claude uses its own tokenizer and its counts differ. Treat this as one consistent yardstick across the catalogue rather than a bill. Prices are per million input tokens.

ModelPer sessionOnce invoked
Fable 5 $0.00460 $0.00460
Opus 5 $0.00230 $0.00230
Sonnet 5 $0.00092 $0.00092
Haiku 4.5 $0.00046 $0.00046

Measured 2d ago against content hash 0ae0ee467746, method: parsed. Prices are Anthropic first-party input rates as of 2026-08-30, from the pricing page.

Security

Grade A, and why

maui collectionview-ios.instructions.md scanned grade A with 0 findings against 26 rules in 11 categories — prompt injection, anti-refusal, data exfiltration, privilege escalation, supply chain, agent snooping, system-prompt leakage, SSRF and excessive agency — measured 2d ago.

A static scan of the body, not an audit. Every finding is printed with the line that produced it so you can judge whether it matters here. A mod is markdown that instructs an agent; that is exactly why what it instructs is worth reading.

Nothing flagged

None of the 26 patterns this scan looks for appear in this file: no shell pipes, no recursive deletes, no credential paths, no hidden text, no instruction-override or anti-refusal phrasing, no agent-config snooping. That is not a guarantee, it is the absence of the things that are checkable.

.github/instructions/collectionview-ios.instructions.md · 35 lines

What it actually says

CollectionView — iOS/MacCatalyst (Items2/ Handler)

New iOS/MacCatalyst work targets Items2/. Items/iOS/ is deprecated. See collectionview-handler-detection.instructions.md for the full platform→handler mapping.

UICollectionView Cell Measurement

  • Scope cell layout invalidation to the affected cell — avoid InvalidateLayout() on the entire collection for single-cell changes
  • Custom UICollectionViewCell subclasses should handle MeasureInvalidated only when the hosted MAUI control actually needs remeasuring
  • Cell sizing must stay in sync between the measure pass and the layout pass — out-of-sync causes visual glitches

UICollectionViewCompositionalLayout

  • Layout configuration must match the ItemsLayout specification (Linear, Grid, or custom)
  • ItemsLayout property changes require full layout reconfiguration — partial updates leave stale section configuration
  • Group header/footer template changes must invalidate the correct section scope, not the entire layout

Memory Management

  • Use static callback patterns to avoid retain cycles between cells and their hosting handler
  • Remove NSNotificationCenter observers in DisconnectHandler
  • Weak references for long-lived observers of short-lived cells — cells are recycled and reused

Regression Patterns

  • Test across empty collection, single item, many items, and with grouping — a fix for one layout scenario routinely breaks another

Items/ iOS (Deprecated)

  • Files in Handlers/Items/*.iOS.cs are deprecated — prefer Items2/ for new work
  • Only modify Items/ iOS code for explicit legacy maintenance or backward-compatibility fixes

Platform file extension rules (.ios.cs vs .maccatalyst.cs compilation targets) are defined in copilot-instructions.md § Platform-Specific File Extensions. See also collectionview-handler-detection.instructions.md for which handler directory to target per platform.

Changes

What this file has done since we first saw it

Hashed on every crawl. A supply-chain change to an agent config is a question of when, not whether, so the history is kept rather than the latest state alone.

  1. 2d ago First seen · 35 lines · 460 tokens per session scan A 0ae0ee467746

Subscribe to this mod's changes

maui collectionview-ios.instructions.md is an instructions file published in the GitHub repository dotnet/maui (23,317 stars, last pushed 2d ago), licensed MIT. It adds 460 tokens to every session, about $0.0023 per session on Opus 5. A static security scan graded it A with 0 findings. No closer match exists in the catalogue, so it is treated as the original; first seen 2026-08-30.

Related

Other instructions, from other repositories