[Shared Element Transition] Problem with headers (#4036)

## Summary

PR contains improvements in snapshotting view properties. 
- Android - Now animation will start when the screen has an attached
header. In effect, the values in the snapshot will be valid.
- iOS - I replaced the old approach by detecting the screen header and
adding information about header size to the snapshot.

android/src/main/java/com/swmansion/reanimated/layoutReanimation/SharedTransitionManager.java

@@ -335,10 +335,6 @@ private View findStack(View view) {
 
   protected void makeSnapshot(View view) {
     Snapshot snapshot = new Snapshot(view);
-    View screen = findScreen(view);
-    if (screen != null) {
-      snapshot.originY -= screen.getTop();
-    }
     mSnapshotRegistry.put(view.getId(), snapshot);
   }
 
@@ -408,7 +404,9 @@ void visitNativeTreeAndMakeSnapshot(View view) {
       return;
     }
     ViewGroup viewGroup = (ViewGroup) view;
-    makeSnapshot(view);
+    if (mAnimationsManager.hasAnimationForTag(view.getId(), "sharedElementTransition")) {
+      makeSnapshot(view);
+    }
     for (int i = 0; i < viewGroup.getChildCount(); i++) {
       View child = viewGroup.getChildAt(i);
       visitNativeTreeAndMakeSnapshot(child);

android/src/reactNativeVersionPatch/nativeHierarchyManager/latest/com/swmansion/reanimated/layoutReanimation/ReanimatedNativeHierarchyManager.java

@@ -254,14 +254,30 @@ public synchronized void updateLayout(
       if (container != null
           && viewManagerName.equals("RNSScreen")
           && mReaLayoutAnimator != null) {
-        ((ReaLayoutAnimator) mReaLayoutAnimator).getAnimationsManager().viewsDidLayout();
+        boolean hasHeader = checkIfTopScreenHasHeader((ViewGroup) container);
+        if (!hasHeader || !container.isLayoutRequested()) {
+          mReaLayoutAnimator.getAnimationsManager().viewsDidLayout();
+        }
       }
     } catch (IllegalViewOperationException e) {
       // (IllegalViewOperationException) == (vm == null)
       e.printStackTrace();
     }
   }
 
+  private boolean checkIfTopScreenHasHeader(ViewGroup screenStack) {
+    try {
+      ViewGroup fragment = (ViewGroup)screenStack.getChildAt(0);
+      ViewGroup screen = (ViewGroup)fragment.getChildAt(0);
+      View headerConfig = screen.getChildAt(0);
+      Field field = headerConfig.getClass().getDeclaredField("mIsHidden");
+      field.setAccessible(true);
+      return !field.getBoolean(headerConfig);
+    } catch (NullPointerException | NoSuchFieldException | IllegalAccessException e) {
+      return false;
+    }
+  }
+
   @Override
   public synchronized void manageChildren(
       int tag,

ios/LayoutReanimation/REASharedTransitionManager.m

@@ -462,7 +462,9 @@ - (void)finishSharedAnimation:(UIView *)view
     BOOL isScreenDetached = [self getScreenForView:view].superview == nil;
     NSNumber *originY = viewSourcePreviousSnapshot.values[@"originY"];
     if (isScreenDetached) {
-      viewSourcePreviousSnapshot.values[@"originY"] = viewSourcePreviousSnapshot.values[@"originYByParent"];
+      float originYByParent = [viewSourcePreviousSnapshot.values[@"originYByParent"] floatValue];
+      float headerHeight = [viewSourcePreviousSnapshot.values[@"headerHeight"] floatValue];
+      viewSourcePreviousSnapshot.values[@"originY"] = @(originYByParent + headerHeight);
     }
     [_animationManager progressLayoutAnimationWithStyle:viewSourcePreviousSnapshot.values
                                                  forTag:view.reactTag

ios/LayoutReanimation/REASnapshot.m

@@ -1,5 +1,6 @@
 #import <Foundation/Foundation.h>
 #import <RNReanimated/REASnapshot.h>
+#import <React/UIView+React.h>
 
 NS_ASSUME_NONNULL_BEGIN
 
@@ -34,6 +35,14 @@ - (void)makeSnapshotForView:(UIView *)view useAbsolutePositionOnly:(BOOL)useAbso
     _values[@"originX"] = _values[@"globalOriginX"];
     _values[@"originY"] = _values[@"globalOriginY"];
     _values[@"originYByParent"] = [NSNumber numberWithDouble:view.center.y - view.bounds.size.height / 2.0];
+
+    UIView *navigationContainer = view.reactViewController.navigationController.view;
+    UIView *header = [navigationContainer.subviews count] > 1 ? navigationContainer.subviews[1] : nil;
+    if (header != nil) {
+      _values[@"headerHeight"] = @(header.frame.size.height);
+    } else {
+      _values[@"headerHeight"] = @(0);
+    }
   } else {
     _values[@"originX"] = [NSNumber numberWithDouble:view.center.x - view.bounds.size.width / 2.0];
     _values[@"originY"] = [NSNumber numberWithDouble:view.center.y - view.bounds.size.height / 2.0];