Adds the ability to use UIManager to check if a node is an ancestor

Examples/UIExplorer/UIExplorerUnitTests/RCTShadowViewTests.m

@@ -106,6 +106,29 @@ - (void)testApplyingLayoutRecursivelyToShadowView
   XCTAssertTrue(CGRectEqualToRect([rightView measureLayoutRelativeToAncestor:self.parentView], CGRectMake(330, 120, 100, 200)));
 }
 
+- (void)testAncestorCheck
+{
+  RCTShadowView *centerView = [self _shadowViewWithConfig:^(CSSNodeRef node) {
+    CSSNodeStyleSetFlex(node, 1);
+  }];
+
+  RCTShadowView *mainView = [self _shadowViewWithConfig:^(CSSNodeRef node) {
+    CSSNodeStyleSetFlex(node, 1);
+  }];
+
+  [mainView insertReactSubview:centerView atIndex:0];
+
+  RCTShadowView *footerView = [self _shadowViewWithConfig:^(CSSNodeRef node) {
+    CSSNodeStyleSetFlex(node, 1);
+  }];
+
+  [self.parentView insertReactSubview:mainView atIndex:0];
+  [self.parentView insertReactSubview:footerView atIndex:1];
+
+  XCTAssertTrue([centerView viewIsDescendantOf:mainView]);
+  XCTAssertFalse([footerView viewIsDescendantOf:mainView]);
+}
+
 - (void)testAssignsSuggestedWidthDimension
 {
   [self _withShadowViewWithStyle:^(CSSNodeRef node) {

React/Modules/RCTUIManager.m

@@ -1226,6 +1226,26 @@ - (void)setNeedsLayout
   }];
 }
 
+/**
+ * Returs if the shadow view provided has the `ancestor` shadow view as
+ * an actual ancestor.
+ */
+RCT_EXPORT_METHOD(viewIsDescendantOf:(nonnull NSNumber *)reactTag
+                  ancestor:(nonnull NSNumber *)ancestorReactTag
+                  callback:(RCTResponseSenderBlock)callback)
+{
+  RCTShadowView *shadowView = _shadowViewRegistry[reactTag];
+  RCTShadowView *ancestorShadowView = _shadowViewRegistry[ancestorReactTag];
+  if (!shadowView) {
+    return;
+  }
+  if (!ancestorShadowView) {
+    return;
+  }
+  BOOL viewIsAncestor = [shadowView viewIsDescendantOf:ancestorShadowView];
+  callback(@[@(viewIsAncestor)]);
+}
+
 static void RCTMeasureLayout(RCTShadowView *view,
                              RCTShadowView *ancestor,
                              RCTResponseSenderBlock callback)

React/Views/RCTShadowView.h

@@ -212,4 +212,9 @@ typedef void (^RCTApplierBlock)(NSDictionary<NSNumber *, UIView *> *viewRegistry
  */
 - (CGRect)measureLayoutRelativeToAncestor:(RCTShadowView *)ancestor;
 
+/**
+ * Checks if the current shadow view is a descendant of the provided `ancestor`
+ */
+- (BOOL)viewIsDescendantOf:(RCTShadowView *)ancestor;
+
 @end

React/Views/RCTShadowView.m

@@ -279,6 +279,17 @@ - (CGRect)measureLayoutRelativeToAncestor:(RCTShadowView *)ancestor
   return (CGRect){offset, self.frame.size};
 }
 
+- (BOOL)viewIsDescendantOf:(RCTShadowView *)ancestor
+{
+  NSInteger depth = 30; // max depth to search
+  RCTShadowView *shadowView = self;
+  while (depth && shadowView && shadowView != ancestor) {
+    shadowView = shadowView->_superview;
+    depth--;
+  }
+  return ancestor == shadowView;
+}
+
 - (instancetype)init
 {
   if ((self = [super init])) {