Ensure an ASM enabled node applies its pending layout when enters pre…

…load state

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

Source/ASDisplayNode.mm

@@ -3079,6 +3079,16 @@ - (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 enter preload state as well.
+    // 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 be forced to occur (see __layout and _u_measureNodeWithBoundsIfNecessary:).
+    // The situation should be uncommon, and forcing is necessary to kick off preloading on subnodes.
+    [self layoutIfNeeded];
+  }
+
   [_interfaceStateDelegate didEnterPreloadState];
 }
 

Tests/ASDisplayNodeImplicitHierarchyTests.m

@@ -20,6 +20,7 @@
 #import <XCTest/XCTest.h>
 
 #import <AsyncDisplayKit/AsyncDisplayKit.h>
+#import <AsyncDisplayKit/ASDisplayNode+FrameworkPrivate.h>
 #import "ASDisplayNodeTestsHelper.h"
 
 @interface ASSpecTestDisplayNode : ASDisplayNode
@@ -101,6 +102,47 @@ - (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};