From ff0e94b4e16fc0c62f7b3a4a2e32986dade7dfe1 Mon Sep 17 00:00:00 2001
From: Scott Goodson <scottg@pinterest.com>
Date: Mon, 16 Nov 2015 11:36:10 -0800
Subject: [PATCH] Introduce ASInterfaceState on ASDisplayNode.

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.
---
 AsyncDisplayKit/ASDisplayNode.h               | 22 +++++++++++++++++++
 AsyncDisplayKit/ASDisplayNode.mm              | 12 ++++++++++
 .../Private/ASDisplayNodeInternal.h           |  2 ++
 3 files changed, 36 insertions(+)

diff --git a/AsyncDisplayKit/ASDisplayNode.h b/AsyncDisplayKit/ASDisplayNode.h
index cf9b7a54f3..62663267ec 100644
--- a/AsyncDisplayKit/ASDisplayNode.h
+++ b/AsyncDisplayKit/ASDisplayNode.h
@@ -32,6 +32,27 @@ typedef CALayer *(^ASDisplayNodeLayerBlock)();
  */
 typedef void (^ASDisplayNodeDidLoadBlock)(ASDisplayNode *node);
 
+/**
+ Interface state is available on ASDisplayNode and ASViewController, and
+ allows checking whether a node is in an interface situation where it is prudent to trigger certain
+ actions: measurement, data fetching, display, and visibility (the latter for animations or other onscreen-only effects).
+ */
+
+typedef NS_OPTIONS(NSUInteger, ASInterfaceState)
+{
+  /** The element is not predicted to be onscreen soon and preloading should not be performed */
+  ASInterfaceStateNone          = 1 << 0,
+  /** The element may be added to a view soon that could become visible.  Measure the layout, including size calculation. */
+  ASInterfaceStateMeasureLayout = 1 << 1,
+  /** The element is likely enough to come onscreen that disk and/or network data required for display should be fetched. */
+  ASInterfaceStateFetchData     = 1 << 2,
+  /** The elemant is very likely to become visible, and concurrent rendering should be executed for any -setNeedsDisplay. */
+  ASInterfaceStateDisplay       = 1 << 3,
+  /** The element is physically onscreen by at least 1 pixel.
+   In practice, all other bit fields should also be set when this flag is set. */
+  ASInterfaceStateVisible       = 1 << 4,
+};
+
 /**
  * An `ASDisplayNode` is an abstraction over `UIView` and `CALayer` that allows you to perform calculations about a view
  * hierarchy off the main thread, and could do rendering off the main thread as well.
@@ -160,6 +181,7 @@ typedef void (^ASDisplayNodeDidLoadBlock)(ASDisplayNode *node);
  */
 @property (nonatomic, readonly, retain) CALayer *layer;
 
+@property (nonatomic, readwrite) ASInterfaceState interfaceState;
 
 /** @name Managing dimensions */
 
diff --git a/AsyncDisplayKit/ASDisplayNode.mm b/AsyncDisplayKit/ASDisplayNode.mm
index e7c6e54c0b..394c050128 100644
--- a/AsyncDisplayKit/ASDisplayNode.mm
+++ b/AsyncDisplayKit/ASDisplayNode.mm
@@ -1684,6 +1684,18 @@ void recursivelyEnsureDisplayForLayer(CALayer *layer)
   [self clearFetchedData];
 }
 
+- (ASInterfaceState)interfaceState
+{
+  return _interfaceState;
+}
+
+- (void)setInterfaceState:(ASInterfaceState)interfaceState
+{
+  if (interfaceState != _interfaceState) {
+    _interfaceState = interfaceState;
+  }
+}
+
 - (void)layout
 {
   ASDisplayNodeAssertMainThread();
diff --git a/AsyncDisplayKit/Private/ASDisplayNodeInternal.h b/AsyncDisplayKit/Private/ASDisplayNodeInternal.h
index cf0681b72b..4953a5b538 100644
--- a/AsyncDisplayKit/Private/ASDisplayNodeInternal.h
+++ b/AsyncDisplayKit/Private/ASDisplayNodeInternal.h
@@ -72,6 +72,8 @@ typedef NS_OPTIONS(NSUInteger, ASDisplayNodeMethodOverrides) {
   NSMutableSet *_pendingDisplayNodes;
 
   _ASPendingState *_pendingViewState;
+  
+  ASInterfaceState _interfaceState;
 
   struct ASDisplayNodeFlags {
     // public properties