Before, it was expensive to check this value, even though it was rarely set.
Now the cost is moved to setting the value, and is made very cheap to check with _hierarchyState.
Later, this will be added to ASViewController. Right now it is not hooked up to drive anything.
It will become the codepath that drives calls like -fetchData and -clearContents.
This ensures memory cleanup happens correctly and introduces a new test project
to support developing new features while stressing tough use cases for correctness.
This provides internal features on _ASAsyncTransaction and ASDisplayNode to facilitate
implementing public API that allows clients to choose if they would prefer to block
on the completion of unfinished rendering, rather than allow a placeholder state to
become visible.
The internal features are:
-[_ASAsyncTransaction waitUntilComplete]
-[ASDisplayNode recursivelyEnsureDisplay]
Also provided are two such implementations:
-[ASCellNode setNeverShowPlaceholders:], which integrates with both Tables and Collections
-[ASViewController setNeverShowPlaceholders:], which should work with Nav and Tab controllers.
Lastly, on ASDisplayNode, a new property .shouldBypassEnsureDisplay allows individual node types
to exempt themselves from blocking the main thread on their display.
By implementing the feature at the ASCellNode level rather than ASTableView & ASCollectionView,
developers can retain fine-grained control on display characteristics. For example, certain
cell types may be appropriate to display to the user with placeholders, whereas others may not.
Follow-up work will include unit tests, revisiting names, and the header locations of definitions.
- -layoutSpecThatFits: must return an ASLayoutSpec.
- Move ASDisplayNode's -measureWithSizeRange: redeclaration to ASDisplayNode.h.
- Rename ASStackLayoutChild.h to ASStackLayoutDefines.h.
- Rename ASStaticLayoutSpecDimension.h to ASRelativeSize.h.
- Don't import ASLayout.h in other headers to prevent circular inclusions.
- Explain use cases of ASLayout's initializers.
- Clean up ASInternalHelpers.h.
- constrainedSizeForCalculatedLayout is of type ASSizeRange.
- calculatedLayout is better explained.
- Since ASLayout is cached and reused, its position property is mutable.
- Introduce ASLayoutNode and its subclasses.
- ASDisplayNode measures its ASLayoutNode and cache the result (ASLayout). Calculated size and position of each subnode can be retrieved from the calculated layout.
- Custom nodes need to override -layoutNodeThatFits:(CGSize) instead of -calculateSizeThatFits:(CGSize).
- Custom nodes do not need to layout its subnodes (in -layout:) anymore. ASDisplayNode can handle the job most of the time, by walking through its layout tree.
- ASCompositeNode is used to embed (display) subnodes to a node's layout. That way, each subnode will also be measured while the parent node is measuring. And the parent node knows where its subnodes are within its layout.
These have been superseded by -[ASDisplayNode initWithViewBlock:] and
-[ASDisplayNode initWithLayerBlock:], respectively -- the new API allows
for custom initialisers, but does not support asynchronous display.
The old initialisers are still available in ASDisplayNodeInternal.h, for
internal subclasses and daring adventurers.
This adds new initializer methods to ASDisplayNode:
```objc
initWithViewBlock:(ASDisplayNodeViewBlock)viewBlock
initWithLayerBlock:(ASDisplayNodeLayerBlock)layerBlock
```
Sometimes a view can't be constructed with `-[initWithViewClass:]` but you want to use it with ASDK, so these new methods provide a way to wrap an existing view in a node.
The API is meant to preserve ASDisplayNode's behavior, so you can still construct and set properties on the node on a background queue before its view is loaded; even though the view was created a priori, it is not considered to be loaded until `node.view` is accessed.
Using the API looks like this:
dispatch_async(backgroundQueue, ^{
ASDisplayNode *node = [ASDisplayNode alloc] initWithViewBlock:^{
// Guaranteed to run on the main queue
UIButton *button = [UIButton buttonWithType:UIButtonTypeSystem];
[button sizeToFit];
node.frame = button.frame;
return button;
}];
// Use `node` as you normally would...
node.backgroundColor = [UIColor redColor];
});
The main thing this bridging API doesn't do (can't do?) is layout. Methods like `-[ASDisplayNode calculateSizeThatFits:]` and `-[ASDisplayNode layout]` cannot delegate to `[UIView sizeThatFits:]` and `[UIView layoutSubviews]` since the UIView methods must run on the main thread. If ASDK were internally asynchronous and could dispatch its layout methods to different threads (sort of like how ASTableView computes its cells' layouts) then we could mark nodes with externally provided views/layers as having "main-queue affinity" and delegate its layout to UIKit.
Test cases are included and all existing tests pass.
ASDisplayNodes now have an overidable method -placeholderImage that lets you provide a custom UIImage to display while a node is displaying asyncronously. The default implementation of this method returns nil and thus does nothing. A provided example project also demonstrates using the placeholder API.
Postpone manual display until a future release when it can be called on any thread. Provide the current node manual display logic as a category on ASDisplayNode only available for ASRangeController. Deprecate -displayImmediately.
Rename the ASDisplayNode property to match its _ASDisplayLayer
counterpart -- `displaySuspended` is more succinct and is a more
plausible name for a Cocoa BOOL property.
This is a remnant from before `willAppear` and `didDisappear` were
renamed to better reflect their hierarchy-change status (being added to
the hierarchy != being visible). May be useful for turians.
* Reorganise and rename `_flags` for clarity and consistency.
* Remove ambiguity between `implementsDisplay` and `hasClassDisplay`.
* Delete useless `hasWillDisplayAsyncLayer` check -- make it a simple
subclass override point, as with `didDisplayAsyncLayer:`.
* Minor comment cleanup.
ASImageNode and ASHighlightOverlayLayer were both using
[[UIScreen mainScreen] scale] directly. Bad. No cookie. Use
ASDisplayNodeScreenScale() instead.
(Also, regenerate Xcode project with Xcode 6 and current CocoaPods.)
ASDisplayNode and several subclasses had previously cleared memory-heavy
objects like the backing store and text layout manager when the node's
view
or layer is removed from a visible heirarchy. This works great in any
system
that uses a "working range", where exiting the range removes the node
from
the hierarchy and reclaiming memory at that time is important.
However, for
standard UIViewController patterns (unused in Paper), this behavior
causes
highly undesirable thrashing (leading to visible flashes & wasteful
re-rendering of content).
After this change, node subclasses should implement -reclaimMemory if
they
need to perform any other cleanup besides backing store destruction
when they
leave a working range or other scenario where memory reduction is
valuable.
To trigger this behavior, calling code should use
-recursivelyReclaimMemory.
r=nadi
