fix: properly handle floating header height

Previously, the header height wasn't stored per screen. This resulted in header height always referring to the one in last mounted screen.
As a result, the top margin for screens were incorrect.

This resulted in bugs such as when you go to a screen with no header, header height will stay 0 even after navigating back.

This commit stores the height for each screen separately, handling this properly.

src/views/Header/HeaderContainer.tsx

@@ -1,11 +1,5 @@
 import * as React from 'react';
-import {
-  View,
-  StyleSheet,
-  LayoutChangeEvent,
-  StyleProp,
-  ViewStyle,
-} from 'react-native';
+import { View, StyleSheet, StyleProp, ViewStyle } from 'react-native';
 import {
   Layout,
   Route,
@@ -22,7 +16,7 @@ export type Props = {
   scenes: Array<HeaderScene<Route> | undefined>;
   navigation: NavigationProp;
   getPreviousRoute: (props: { route: Route }) => Route | undefined;
-  onLayout?: (e: LayoutChangeEvent) => void;
+  onContentHeightChange?: (props: { route: Route; height: number }) => void;
   styleInterpolator: HeaderStyleInterpolator;
   style?: StyleProp<ViewStyle>;
 };
@@ -33,7 +27,7 @@ export default function HeaderContainer({
   layout,
   navigation,
   getPreviousRoute,
-  onLayout,
+  onContentHeightChange,
   styleInterpolator,
   style,
 }: Props) {
@@ -91,7 +85,15 @@ export default function HeaderContainer({
         return (
           <View
             key={scene.route.key}
-            onLayout={onLayout}
+            onLayout={
+              onContentHeightChange
+                ? e =>
+                    onContentHeightChange({
+                      route: scene.route,
+                      height: e.nativeEvent.layout.height,
+                    })
+                : undefined
+            }
             pointerEvents="box-none"
             accessibilityElementsHidden={!isFocused}
             importantForAccessibility={

src/views/Stack/Stack.tsx

@@ -60,7 +60,7 @@ type State = {
   scenes: HeaderScene<Route>[];
   progress: ProgressValues;
   layout: Layout;
-  floatingHeaderHeight: number;
+  floatingHeaderHeights: { [key: string]: number };
 };
 
 const dimensions = Dimensions.get('window');
@@ -92,6 +92,23 @@ const { cond, eq } = Animated;
 
 const ANIMATED_ONE = new Animated.Value(1);
 
+const getFloatingHeaderHeights = (
+  routes: Route[],
+  layout: Layout,
+  previous: { [key: string]: number }
+) => {
+  const defaultHeaderHeight = getDefaultHeaderHeight(layout);
+
+  return routes.reduce(
+    (acc, curr) => {
+      acc[curr.key] = previous[curr.key] || defaultHeaderHeight;
+
+      return acc;
+    },
+    {} as { [key: string]: number }
+  );
+};
+
 export default class Stack extends React.Component<Props, State> {
   static getDerivedStateFromProps(props: Props, state: State) {
     if (
@@ -157,6 +174,11 @@ export default class Stack extends React.Component<Props, State> {
       }),
       progress,
       descriptors: props.descriptors,
+      floatingHeaderHeights: getFloatingHeaderHeights(
+        props.routes,
+        state.layout,
+        state.floatingHeaderHeights
+      ),
     };
   }
 
@@ -171,7 +193,7 @@ export default class Stack extends React.Component<Props, State> {
     // This is not a great heuristic here. We don't know synchronously
     // on mount what the header height is so we have just used the most
     // common cases here.
-    floatingHeaderHeight: getDefaultHeaderHeight(layout),
+    floatingHeaderHeights: {},
   };
 
   private handleLayout = (e: LayoutChangeEvent) => {
@@ -186,15 +208,35 @@ export default class Stack extends React.Component<Props, State> {
 
     const layout = { width, height };
 
-    this.setState({ layout });
+    this.setState({
+      layout,
+      floatingHeaderHeights: getFloatingHeaderHeights(
+        this.props.routes,
+        layout,
+        {}
+      ),
+    });
   };
 
-  private handleFloatingHeaderLayout = (e: LayoutChangeEvent) => {
-    const { height } = e.nativeEvent.layout;
+  private handleFloatingHeaderLayout = ({
+    route,
+    height,
+  }: {
+    route: Route;
+    height: number;
+  }) => {
+    const previousHeight = this.state.floatingHeaderHeights[route.key];
 
-    if (height !== this.state.floatingHeaderHeight) {
-      this.setState({ floatingHeaderHeight: height });
+    if (previousHeight && previousHeight === height) {
+      return;
     }
+
+    this.setState(state => ({
+      floatingHeaderHeights: {
+        ...state.floatingHeaderHeights,
+        [route.key]: height,
+      },
+    }));
   };
 
   private handleTransitionStart = ({
@@ -238,7 +280,7 @@ export default class Stack extends React.Component<Props, State> {
       onGestureEnd,
     } = this.props;
 
-    const { scenes, layout, progress, floatingHeaderHeight } = this.state;
+    const { scenes, layout, progress, floatingHeaderHeights } = this.state;
 
     const focusedRoute = navigation.state.routes[navigation.state.index];
     const focusedOptions = descriptors[focusedRoute.key].options;
@@ -320,7 +362,7 @@ export default class Stack extends React.Component<Props, State> {
                   onGestureCanceled={onGestureCanceled}
                   onGestureEnd={onGestureEnd}
                   gestureResponseDistance={gestureResponseDistance}
-                  floatingHeaderHeight={floatingHeaderHeight}
+                  floatingHeaderHeight={floatingHeaderHeights[route.key]}
                   hasCustomHeader={header === null}
                   getPreviousRoute={getPreviousRoute}
                   headerMode={headerMode}
@@ -348,7 +390,7 @@ export default class Stack extends React.Component<Props, State> {
               scenes,
               navigation,
               getPreviousRoute,
-              onLayout: this.handleFloatingHeaderLayout,
+              onContentHeightChange: this.handleFloatingHeaderLayout,
               styleInterpolator:
                 focusedOptions.headerStyleInterpolator !== undefined
                   ? focusedOptions.headerStyleInterpolator