[Foundation] Fix nullability in NSMutableDictionary. #24428

rolfbjarne · 2025-12-12T09:50:26Z

Enable nullability for NSMutableDictionary.cs.
Fix interface implementations to match nullability contracts (IDictionary, IDictionary<NSObject, NSObject>).
Make indexers' return type allow null, but disallow setting null values.
Remove all 'To be added.' XML comments.
Add comprehensive XML documentation for all public methods, properties, and indexers.
Use proper 'see cref' attributes for type references in documentation.
Fix ArgumentNullException to use nameof for parameter names.
Remove an unused constructor.

Also add NSMutableDictionary tests for missing key behavior:

Add tests to verify that accessing missing keys returns null.
Test all indexer overloads (string, NSObject, NSString).
Test ObjectForKey method with missing keys.
Test TryGetValue with missing keys returns false and null output.
Test IDictionary interface implementations (indexer and Contains).
Ensure existing keys still work correctly after testing missing keys.

These tests document and verify the expected behavior when fetching
values for keys that don't exist in the dictionary.

This is file 34 of 47 files with nullability disabled in Foundation.

Contributes towards #17285.

* Enable nullability for NSMutableDictionary.cs. * Fix interface implementations to match nullability contracts (IDictionary, IDictionary<NSObject, NSObject>). * Make indexers' return type allow null, but disallow setting null values. * Remove all 'To be added.' XML comments. * Add comprehensive XML documentation for all public methods, properties, and indexers. * Use proper 'see cref' attributes for type references in documentation. * Fix ArgumentNullException to use nameof for parameter names. * Remove an unused constructor. Also add NSMutableDictionary tests for missing key behavior: * Add tests to verify that accessing missing keys returns null. * Test all indexer overloads (string, NSObject, NSString). * Test ObjectForKey method with missing keys. * Test TryGetValue with missing keys returns false and null output. * Test IDictionary interface implementations (indexer and Contains). * Ensure existing keys still work correctly after testing missing keys. These tests document and verify the expected behavior when fetching values for keys that don't exist in the dictionary. This is file 34 of 47 files with nullability disabled in Foundation. Contributes towards #17285.

Copilot

Pull request overview

This PR enables nullable reference types for NSMutableDictionary.cs (file 34 of 47) and updates related code that depends on it. The changes ensure proper nullability contracts for dictionary operations, particularly handling the case where missing keys return null, while preventing null value assignments. The PR also adds comprehensive XML documentation and test coverage for missing key scenarios.

Key changes:

Enable nullability for NSMutableDictionary and update indexers to return nullable NSObject while disallowing null value assignments using [DisallowNull] attribute
Add comprehensive XML documentation replacing "To be added" placeholders
Add tests verifying null return behavior for missing keys across all indexer overloads
Update dependent files across multiple frameworks to handle nullable dictionary returns

Reviewed changes

Copilot reviewed 13 out of 13 changed files in this pull request and generated 4 comments.

Show a summary per file

File	Description
src/Foundation/NSMutableDictionary.cs	Enables nullability, adds comprehensive XML docs, fixes ArgumentNullException to use nameof, adds [DisallowNull] attributes on indexers
src/Foundation/NSDictionary.cs	Adds nullable annotations to indexers in base class, adds [DisallowNull] attributes
tests/monotouch-test/Foundation/NSMutableDictionaryTest.cs	Adds 7 new tests verifying null return behavior for missing keys across different indexer overloads and methods
tests/cecil-tests/Documentation.KnownFailures.txt	Removes entries for newly documented NSMutableDictionary members
src/WebKit/WebNavigationPolicyEventArgs.cs	Updates to handle nullable dictionary indexer returns with null-coalescing operators
src/Security/Items.cs	Adds null check after dictionary lookup before constructing SecRecord
src/SceneKit/SCNParticleSystem.cs	Adds ArgumentNullException.ThrowIfNull for dictionary value parameter
src/Foundation/NSUrlSessionHandler.cs	Updates to use pattern matching for safer dictionary value retrieval
src/CoreText/CTTextTab.cs	Adds nullable annotation and null-forgiving operator for dictionary lookup
src/CoreText/CTFontDescriptor.cs	Adds nullable casts and null checks for dictionary lookups
src/CoreText/CTFont.cs	Adds null checks and default returns for dictionary lookups returning NSNumber
src/AudioToolbox/AudioToolbox.cs	Adds nullable annotation for dictionary value property
src/AudioToolbox/AudioFile.cs	Updates to check for null dictionary before constructing AudioFileInfoDictionary

src/Foundation/NSDictionary.cs

src/SceneKit/SCNParticleSystem.cs

tests/monotouch-test/Foundation/NSMutableDictionaryTest.cs

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

vs-mobiletools-engineering-service2 · 2025-12-15T10:29:51Z

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vs-mobiletools-engineering-service2 · 2025-12-15T10:56:31Z

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vs-mobiletools-engineering-service2 · 2025-12-15T11:13:17Z

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vs-mobiletools-engineering-service2 · 2025-12-15T11:21:45Z

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vs-mobiletools-engineering-service2 · 2025-12-15T11:27:13Z

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vs-mobiletools-engineering-service2 · 2025-12-15T11:43:38Z

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vs-mobiletools-engineering-service2 · 2025-12-15T13:17:40Z

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rolfbjarne requested a review from dalexsoto as a code owner December 12, 2025 09:50

rolfbjarne requested a review from Copilot December 12, 2025 09:50

Copilot started reviewing on behalf of rolfbjarne December 12, 2025 09:51 View session

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dalexsoto approved these changes Dec 12, 2025

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Update src/Foundation/NSDictionary.cs

d883529

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

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rolfbjarne added 2 commits December 15, 2025 10:58

Remove on null value.

49a84c0

Be sure to resolve to the expected indexer overload in test.

b61b97b

rolfbjarne enabled auto-merge (squash) December 15, 2025 09:58

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rolfbjarne merged commit 05c9830 into main Dec 15, 2025
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[Foundation] Fix nullability in NSMutableDictionary. #24428

[Foundation] Fix nullability in NSMutableDictionary. #24428

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vs-mobiletools-engineering-service2 commented Dec 15, 2025

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