Ensure an ASM enabled node applies its pending layout when enters preload state (facebookarchive#706)

This makes sure subnodes are inserted and start preloading right away, instead of waiting until the next layout pass of the supernode. Fixes facebookarchive#693.

Author: nguyenhuy

CHANGELOG.md

@@ -16,6 +16,7 @@
 - [ASScrollNode] Ensure the node respects the given size range while calculating its layout. [#637](https://github.com/TextureGroup/Texture/pull/637) [Huy Nguyen](https://github.com/nguyenhuy)
 - [ASScrollNode] Invalidate the node's calculated layout if its scrollable directions changed. Also add unit tests for the class. [#637](https://github.com/TextureGroup/Texture/pull/637) [Huy Nguyen](https://github.com/nguyenhuy)
 - Add new unit testing to the layout engine. [Adlai Holler](https://github.com/Adlai-Holler) [#424](https://github.com/TextureGroup/Texture/pull/424)
+- [Automatic Subnode Management] Nodes with ASM enabled now insert/delete their subnodes as soon as they enter preload state, so the subnodes can preload too. [Huy Nguyen](https://github.com/nguyenhuy) [#706](https://github.com/TextureGroup/Texture/pull/706)
 
 ## 2.6
 - [Xcode 9] Updated to require Xcode 9 (to fix warnings) [Garrett Moon](https://github.com/garrettmoon)

Source/ASDisplayNode.mm

@@ -3079,6 +3079,20 @@ - (void)didEnterPreloadState
 {
   ASDisplayNodeAssertMainThread();
   ASDisplayNodeAssertLockUnownedByCurrentThread(__instanceLock__);
+
+  if (self.automaticallyManagesSubnodes) {
+    // Tell the node to apply its applicable pending layout, if any, so that its subnodes are inserted/deleted
+    // and start preloading right away.
+    //
+    // If this node has an up-to-date layout (and subnodes), calling layoutIfNeeded will be fast.
+    //
+    // If this node doesn't have a calculated or pending layout that fits its current bounds, a measurement pass will occur
+    // (see __layout and _u_measureNodeWithBoundsIfNecessary:).
+    // This scenario should be uncommon, and running a measurement pass here is a fine trade-off because preloading
+    // any time after this point would be late.
+    [self layoutIfNeeded];
+  }
+
   [_interfaceStateDelegate didEnterPreloadState];
 }
 

Tests/ASDisplayNodeImplicitHierarchyTests.m

@@ -2,8 +2,6 @@
 //  ASDisplayNodeImplicitHierarchyTests.m
 //  Texture
 //
-//  Created by Levi McCallum on 2/1/16.
-//
 //  Copyright (c) 2014-present, Facebook, Inc.  All rights reserved.
 //  This source code is licensed under the BSD-style license found in the
 //  LICENSE file in the /ASDK-Licenses directory of this source tree. An additional
@@ -20,6 +18,7 @@
 #import <XCTest/XCTest.h>
 
 #import <AsyncDisplayKit/AsyncDisplayKit.h>
+#import <AsyncDisplayKit/ASDisplayNode+FrameworkPrivate.h>
 #import "ASDisplayNodeTestsHelper.h"
 
 @interface ASSpecTestDisplayNode : ASDisplayNode
@@ -101,6 +100,47 @@ - (void)testInitialNodeInsertionWithOrdering
   XCTAssertEqual(node.subnodes[4], node5);
 }
 
+- (void)testInitialNodeInsertionWhenEnterPreloadState
+{
+  static CGSize kSize = {100, 100};
+
+  static NSInteger subnodeCount = 5;
+  NSMutableArray<ASDisplayNode *> *subnodes = [NSMutableArray arrayWithCapacity:subnodeCount];
+  for (NSInteger i = 0; i < subnodeCount; i++) {
+    ASDisplayNode *subnode = [[ASDisplayNode alloc] init];
+    // As we will involve a stack spec we have to give the nodes an intrinsic content size
+    subnode.style.preferredSize = kSize;
+    [subnodes addObject:subnode];
+  }
+
+  ASSpecTestDisplayNode *node = [[ASSpecTestDisplayNode alloc] init];
+  node.automaticallyManagesSubnodes = YES;
+  node.layoutSpecBlock = ^(ASDisplayNode *weakNode, ASSizeRange constrainedSize) {
+    ASAbsoluteLayoutSpec *absoluteLayout = [ASAbsoluteLayoutSpec absoluteLayoutSpecWithChildren:@[subnodes[3]]];
+
+    ASStackLayoutSpec *stack1 = [[ASStackLayoutSpec alloc] init];
+    [stack1 setChildren:@[subnodes[0], subnodes[1]]];
+
+    ASStackLayoutSpec *stack2 = [[ASStackLayoutSpec alloc] init];
+    [stack2 setChildren:@[subnodes[2], absoluteLayout]];
+
+    return [ASAbsoluteLayoutSpec absoluteLayoutSpecWithChildren:@[stack1, stack2, subnodes[4]]];
+  };
+
+  ASDisplayNodeSizeToFitSizeRange(node, ASSizeRangeMake(CGSizeZero, CGSizeMake(CGFLOAT_MAX, CGFLOAT_MAX)));
+  [node recursivelySetInterfaceState:ASInterfaceStatePreload];
+
+  // No premature view allocation
+  XCTAssertFalse(node.isNodeLoaded);
+  // Subnodes should be inserted, laid out and entered preload state
+  XCTAssertTrue([subnodes isEqualToArray:node.subnodes]);
+  for (NSInteger i = 0; i < subnodeCount; i++) {
+    ASDisplayNode *subnode = subnodes[i];
+    XCTAssertTrue(CGSizeEqualToSize(kSize, subnode.bounds.size));
+    XCTAssertTrue(ASInterfaceStateIncludesPreload(subnode.interfaceState));
+  }
+}
+
 - (void)testCalculatedLayoutHierarchyTransitions
 {
   static CGSize kSize = {100, 100};