Merge pull request #1005 from facebook/ASDisplayNodeContentsPreservation

[ASDisplayNode] Preserve contents after non-range-managed nodes are removed from superviews or windows.

Author: appleguy

AsyncDisplayKit/ASDisplayNode.mm

@@ -1770,23 +1770,31 @@ - (void)setInterfaceState:(ASInterfaceState)newState
     // Trigger asynchronous measurement if it is not already cached or being calculated.
   }
 
+  // For the FetchData and Display ranges, we don't want to call -clear* if not being managed by a range controller.
+  // Otherwise we get flashing behavior from normal UIKit manipulations like navigation controller push / pop.
+  // Still, the interfaceState should be updated to the current state of the node; just don't act on the transition.
+  
   // Entered or exited data loading state.
   if ((newState & ASInterfaceStateFetchData) != (oldState & ASInterfaceStateFetchData)) {
     if (newState & ASInterfaceStateFetchData) {
       [self fetchData];
     } else {
-      [self clearFetchedData];
+      if ([self supportsRangeManagedInterfaceState]) {
+        [self clearFetchedData];
+      }
     }
   }
 
   // Entered or exited contents rendering state.
   if ((newState & ASInterfaceStateDisplay) != (oldState & ASInterfaceStateDisplay)) {
-    if (newState & ASInterfaceStateDisplay) {
-      // Once the working window is eliminated (ASRangeHandlerRender), trigger display directly here.
-      [self setDisplaySuspended:NO];
-    } else {
-      [self setDisplaySuspended:YES];
-      [self clearContents];
+    if ([self supportsRangeManagedInterfaceState]) {
+      if (newState & ASInterfaceStateDisplay) {
+        // Once the working window is eliminated (ASRangeHandlerRender), trigger display directly here.
+        [self setDisplaySuspended:NO];
+      } else {
+        [self setDisplaySuspended:YES];
+        [self clearContents];
+      }
     }
   }
 

AsyncDisplayKitTests/ASDisplayNodeTests.m

@@ -1702,7 +1702,11 @@ - (void)testInterfaceStateForNonCellNode
   XCTAssert(node.interfaceState == ASInterfaceStateInHierarchy);
 
   [node.view removeFromSuperview];
-  XCTAssert(!node.hasFetchedData);
+  // We don't want to call -clearFetchedData on nodes that aren't being managed by a range controller.
+  // Otherwise we get flashing behavior from normal UIKit manipulations like navigation controller push / pop.
+  // Still, the interfaceState should be None to reflect the current state of the node.
+  // We just don't proactively clear contents or fetched data for this state transition.
+  XCTAssert(node.hasFetchedData);
   XCTAssert(node.interfaceState == ASInterfaceStateNone);
 }