# CATransaction A mechanism for grouping multiple layer-tree operations into atomic updates to the render tree. ``` class CATransaction ``` ## Overview `CATransaction` is the Core Animation mechanism for batching multiple layer-tree operations into atomic updates to the render tree. Every modification to a layer tree must be part of a transaction. Nested transactions are supported. Core Animation supports two types of transactions: *implicit* transactions and *explicit* transactions. Implicit transactions are created automatically when the layer tree is modified by a thread without an active transaction and are committed automatically when the thread’s runloop next iterates. Explicit transactions occur when the the application sends the [`CATransaction`](/documentation/QuartzCore/CATransaction) class a [`begin()`](/documentation/QuartzCore/CATransaction/begin()) message before modifying the layer tree, and a [`commit()`](/documentation/QuartzCore/CATransaction/commit()) message afterwards. [`CATransaction`](/documentation/QuartzCore/CATransaction) allows you to override default animation properties that are set for animatable properties. You can customize duration, timing function, whether changes to properties trigger animations, and provide a handler that informs you when all animations from the transaction group are completed. During a transaction you can temporarily acquire a recursive spin lock for managing property atomicity. [`CATransaction`](/documentation/QuartzCore/CATransaction) supports nested transactions. The following code shows how you can fade out a layer (named `transitioningLayer`) over a 2 second duration while scaling it to three times its original size. The scale animation is within a nested transaction with its own duration of 1 second. After the outer transaction completes, a completion block removes `transitioningLayer` from its parent layer. ```swift let transitioningLayer = CALayer() // Outer transaction animates `opacity` to 0 over 2 seconds CATransaction.begin() CATransaction.setAnimationDuration(2) CATransaction.setCompletionBlock { transitioningLayer.removeFromSuperlayer() } transitioningLayer.opacity = 0 // Inner transaction animates scale to (3, 3, 3) over 1 second CATransaction.begin() CATransaction.setAnimationDuration(1) transitioningLayer.transform = CATransform3DMakeScale(3, 3, 3) CATransaction.commit() // Commits inner transaction CATransaction.commit() // Commits outer transaction ``` ## Topics ### Creating and Committing Transactions [`begin()`](/documentation/QuartzCore/CATransaction/begin()) Begin a new transaction for the current thread. [`commit()`](/documentation/QuartzCore/CATransaction/commit()) Commit all changes made during the current transaction. [`flush()`](/documentation/QuartzCore/CATransaction/flush()) Flushes any extant implicit transaction. ### Overriding Animation Duration and Timing [`animationDuration()`](/documentation/QuartzCore/CATransaction/animationDuration()) Returns the animation duration used by all animations within this transaction group. [`setAnimationDuration(_:)`](/documentation/QuartzCore/CATransaction/setAnimationDuration(_:)) Sets the animation duration used by all animations within this transaction group. [`animationTimingFunction()`](/documentation/QuartzCore/CATransaction/animationTimingFunction()) Returns the timing function used for all animations within this transaction group. [`setAnimationTimingFunction(_:)`](/documentation/QuartzCore/CATransaction/setAnimationTimingFunction(_:)) Sets the timing function used for all animations within this transaction group. ### Temporarily Disabling Property Animations [`disableActions()`](/documentation/QuartzCore/CATransaction/disableActions()) Returns whether actions triggered as a result of property changes made within this transaction group are suppressed. [`setDisableActions(_:)`](/documentation/QuartzCore/CATransaction/setDisableActions(_:)) Sets whether actions triggered as a result of property changes made within this transaction group are suppressed. ### Getting and Setting Completion Block Objects [`completionBlock()`](/documentation/QuartzCore/CATransaction/completionBlock()) Returns the completion block object. [`setCompletionBlock(_:)`](/documentation/QuartzCore/CATransaction/setCompletionBlock(_:)) Sets the completion block object. ### Managing Concurrency [`lock()`](/documentation/QuartzCore/CATransaction/lock()) Attempts to acquire a recursive spin-lock lock, ensuring that returned layer values are valid until unlocked. [`unlock()`](/documentation/QuartzCore/CATransaction/unlock()) Relinquishes a previously acquired transaction lock. ### Getting and Setting Transaction Properties [`setValue(_:forKey:)`](/documentation/QuartzCore/CATransaction/setValue(_:forKey:)) Sets the arbitrary keyed-data for the specified key. [`value(forKey:)`](/documentation/QuartzCore/CATransaction/value(forKey:)) Returns the arbitrary keyed-data specified by the given key. ### Constants [Transaction properties](/documentation/QuartzCore/transaction-properties) These constants define the property keys used by [`value(forKey:)`](/documentation/QuartzCore/CATransaction/value(forKey:)) and [`setValue(_:forKey:)`](/documentation/QuartzCore/CATransaction/setValue(_:forKey:)). --- Copyright © 2026 Apple Inc. All rights reserved. | [Terms of Use](https://www.apple.com/legal/internet-services/terms/site.html) | [Privacy Policy](https://www.apple.com/privacy/privacy-policy)