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Common Developer Mistakes

Common Conceptual Misunderstandings

Common Questions

Accessing the node’s view before it is loaded

Node -init methods are often called off the main thread, therefore it is imperative that no UIKit objects are accessed. Examples of common errors include accessing the node’s view or creating a gesture recognizer. Instead, these operations are ideal to perform in -didLoad.

Interacting with UIKit in -init can cause crashes and performance problems.

Make sure you access your data source outside the node block

The indexPath parameter is only valid outside the node block returned in nodeBlockForItemAtIndexPath: or nodeBlockForRowAtIndexPath:. Because these blocks are executed on a background thread, the indexPath may be invalid by execution time, due to additional changes in the data source.

See an example of how to correctly code a node block in the ASTableNode page. Just as with UIKit, it will cause an exception if Nil is returned from the block for any ASCellNode.

Take steps to avoid a retain cycle in viewBlocks

When using initWithViewBlock: it is important to prevent a retain cycle by capturing a strong reference to self. The two ways that a cycle can be created are by using any instance variable inside the block or directly referencing self without using a weak pointer.

You can use properties instead of instance variables as long as they are accessed on a weak pointer to self.

Because viewBlocks are always executed on the main thread, it is safe to preform UIKit operations (including gesture recognizer creation and addition).

Although the block is destroyed after the view is created, in the event that the block is never run and the view is never created, then a cycle can persist preventing memory from being released.

ASCellNode Reusability

Texture does not use cell reuse, for a number of specific reasons, one side effect of this is that it eliminates the large class of bugs associated with cell reuse.

LayoutSpecs Are Regenerated

A node’s layoutSpec gets regenerated every time its layoutThatFits: method is called.

Layout API Sizing

If you’re confused by ASRelativeDimension, ASRelativeSize, ASRelativeSizeRange and ASSizeRange, check out our Layout API Sizing guide.

CALayer’s .cornerRadius Property Kills Performance

CALayer’s’ .cornerRadius property is a disastrously expensive property that should only be used when there is no alternative. It is one of the least efficient, most render-intensive properties on CALayer (alongside shadowPath, masking, borders, etc). These properties trigger offscreen rendering to perform the clipping operation on every frame — 60FPS during scrolling! — even if the content in that area isn’t changing.

Using .cornerRadius will visually degraded performance on iPhone 4, 4S, and 5 / 5C (along with comparable iPads / iPods) and reduce head room and make frame drops more likely on 5S and newer devices.

For a longer discussion and easy alternative corner rounding solutions, please read our comprehensive corner rounding guide.

Texture does not support UIKit Auto Layout or InterfaceBuilder

UIKit Auto Layout and InterfaceBuilder are not supported by Texture.

However, Texture’s Layout API provides a variety of ASLayoutSpec objects that allow implementing automatic layout which is more efficient (multithreaded, off the main thread), often easier to debug (can step into the code and see where all values come from, as it is open source), and reusable (you can build composable layouts that can be shared with different parts of the UI).

ASDisplayNode keep alive reference

ASTextNode *title=[[ASTextNode alloc]init];
[self addSubnode:title];

retain cycles
"-> _keepalive_node -> ASTextNode ",
"-> _view -> _ASDisplayView "

This retain cycle is intentionally created because the node is in a “live” view hierarchy (it is inside the UIWindow that is onscreen).

To see why this is necessary, consider that Apple also creates this retain cycle between UIView and CALayer. If you create a UIView and add its layer to a super layer, and then release the UIView, it will stay alive even though the CALayer delegate pointing to it is weak.

For the same reason, if the node’s view is a descendant of a window, but there is no reference to the node, we keep the node alive with a strong reference from the view.

Good application design should not rely on this behavior, because a strong reference to the node should be maintained by the subnodes array or by an instance variable. However, this condition occasionally occurs, for example when using a UIView animation API. This cycle should never create a leak or even extend the lifecycle of a node any longer than it is absolutely necessary.

UICollectionViewCell Compatibility

Texture supports using UICollectionViewCells alongside native ASCellNodes.

Note that these UIKit cells will not have the performance benefits of ASCellNodes (like preloading, async layout, and async drawing), even when mixed within the same ASCollectionNode.

However, this interoperability allows developers the flexibility to test out the framework without needing to convert all of their cells at once. Read more here.

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