Add a simple animated header

src/components/Card.tsx

@@ -387,15 +387,15 @@ export default class Card extends React.Component<Props> {
 
 const styles = StyleSheet.create({
   container: {
-    flex: 1
+    flex: 1,
   },
   card: {
     ...StyleSheet.absoluteFillObject,
     shadowOffset: { width: -1, height: 1 },
     shadowRadius: 5,
     shadowColor: '#000',
     backgroundColor: 'white',
-    elevation: 2
+    elevation: 2,
   },
   overlay: {
     ...StyleSheet.absoluteFillObject,

src/components/Header/HeaderAnimated.tsx

@@ -0,0 +1,93 @@
+import * as React from 'react';
+import {
+  View,
+  StyleSheet,
+  Platform,
+  StatusBar,
+  StyleProp,
+  ViewStyle,
+} from 'react-native';
+import Animated from 'react-native-reanimated';
+import HeaderSheet from './HeaderSheet';
+import { Route, Layout } from '../Stack';
+import HeaderAnimatedItem, {
+  HeaderAnimationPreset,
+  InterpolationProps,
+} from './HeaderAnimatedItem';
+
+type Scene<T extends Route> = {
+  title: string;
+  route: T;
+  progress: Animated.Node<number>;
+};
+
+type Props<T extends Route> = {
+  layout: Layout;
+  onGoBack: (props: { route: T }) => void;
+  preset: HeaderAnimationPreset;
+  scenes: Scene<T>[];
+  style?: StyleProp<ViewStyle>;
+};
+
+const { interpolate, multiply } = Animated;
+
+const FadePreset: HeaderAnimationPreset = {
+  styleInterpolator: ({ current, next }: InterpolationProps) => {
+    const progress = next
+      ? multiply(
+          current,
+          interpolate(next, {
+            inputRange: [0, 1],
+            outputRange: [1, 0],
+          })
+        )
+      : current;
+
+    return {
+      leftButtonStyle: { opacity: progress },
+      titleStyle: { opacity: progress },
+    };
+  },
+};
+
+export default class HeaderAnimated<T extends Route> extends React.Component<
+  Props<T>
+> {
+  static defaultProps = {
+    preset: FadePreset,
+  };
+
+  render() {
+    const { preset, scenes, layout, onGoBack } = this.props;
+
+    return (
+      <HeaderSheet>
+        <View style={styles.container}>
+          {scenes.map((scene, i, self) => {
+            const previous = self[i - 1];
+            const next = self[i + 1];
+
+            return (
+              <HeaderAnimatedItem
+                key={scene.route.key}
+                preset={preset}
+                layout={layout}
+                scene={scene}
+                previous={previous}
+                next={next}
+                onGoBack={() => onGoBack({ route: scene.route })}
+              />
+            );
+          })}
+        </View>
+      </HeaderSheet>
+    );
+  }
+}
+
+const styles = StyleSheet.create({
+  container: {
+    height: Platform.OS === 'ios' ? 44 : 56,
+    marginTop: Platform.OS === 'ios' ? 20 : StatusBar.currentHeight,
+  },
+});

src/components/Header/HeaderAnimatedItem.tsx

@@ -0,0 +1,104 @@
+import * as React from 'react';
+import { View, StyleSheet, StyleProp, ViewStyle } from 'react-native';
+import Animated from 'react-native-reanimated';
+import HeaderTitle from './HeaderTitle';
+import { Route, Layout } from '../Stack';
+import HeaderBackButton from './HeaderBackButton';
+import memoize from '../../utils/memoize';
+
+export type InterpolationProps = {
+  current: Animated.Node<number>;
+  next?: Animated.Node<number>;
+  layout: Layout;
+};
+
+export type StyleInterpolator = (
+  props: InterpolationProps
+) => {
+  leftButtonStyle: any;
+  titleStyle: any;
+};
+
+export type HeaderAnimationPreset = {
+  styleInterpolator: StyleInterpolator;
+};
+
+export type Scene<T extends Route> = {
+  title: string;
+  route: T;
+  progress: Animated.Node<number>;
+};
+
+type Props<T extends Route> = {
+  layout: Layout;
+  onGoBack: () => void;
+  preset: HeaderAnimationPreset;
+  scene: Scene<T>;
+  previous?: Scene<T>;
+  next?: Scene<T>;
+  style?: StyleProp<ViewStyle>;
+};
+
+export default class HeaderAnimatedItem<
+  T extends Route
+> extends React.Component<Props<T>> {
+  private getInterpolatedStyle = memoize(
+    (
+      styleInterpolator: StyleInterpolator,
+      layout: Layout,
+      current: Animated.Node<number>,
+      next?: Animated.Node<number>
+    ) => styleInterpolator({ current, next, layout })
+  );
+
+  render() {
+    const {
+      scene,
+      previous,
+      next,
+      preset,
+      layout,
+      onGoBack,
+      style,
+    } = this.props;
+
+    const { titleStyle, leftButtonStyle } = this.getInterpolatedStyle(
+      preset.styleInterpolator,
+      layout,
+      scene.progress,
+      next ? next.progress : undefined
+    );
+
+    return (
+      <View style={[styles.content, style]}>
+        {previous ? (
+          <Animated.View style={[styles.left, leftButtonStyle]}>
+            <HeaderBackButton onPress={onGoBack} title={previous.title} />
+          </Animated.View>
+        ) : null}
+        <HeaderTitle style={[previous ? styles.title : null, titleStyle]}>
+          {scene.title}
+        </HeaderTitle>
+      </View>
+    );
+  }
+}
+
+const styles = StyleSheet.create({
+  content: {
+    ...StyleSheet.absoluteFillObject,
+    paddingHorizontal: 4,
+    flexDirection: 'row',
+    alignItems: 'center',
+  },
+  left: {
+    position: 'absolute',
+    left: 0,
+    top: 0,
+    bottom: 0,
+    justifyContent: 'center',
+  },
+  title: {
+    marginHorizontal: 48,
+  },
+});

src/components/Header/HeaderBackButton.tsx

@@ -41,6 +41,7 @@ class HeaderBackButton extends React.Component<Props, State> {
       ios: '#037aff',
       web: '#5f6368',
     }),
+    backTitleVisible: Platform.OS === 'ios',
     truncatedTitle: 'Back',
   };
 
@@ -163,7 +164,7 @@ const styles = StyleSheet.create({
     width: 36,
     margin: 6,
     alignItems: 'center',
-    justifyContent: 'center'
+    justifyContent: 'center',
   },
   container: {
     alignItems: 'center',

src/components/Header/HeaderSimple.tsx

@@ -1,17 +1,25 @@
 import * as React from 'react';
-import { View, StyleSheet, Platform, StatusBar } from 'react-native';
+import {
+  View,
+  StyleSheet,
+  Platform,
+  StatusBar,
+  StyleProp,
+  ViewStyle,
+} from 'react-native';
 import HeaderBackButton from './HeaderBackButton';
 import HeaderTitle from './HeaderTitle';
 import HeaderSheet from './HeaderSheet';
 
 type Props = {
   title: string;
   onGoBack?: () => void;
+  style?: StyleProp<ViewStyle>;
 };
 
-export default function HeaderAndroid({ title, onGoBack }: Props) {
+export default function HeaderAndroid({ title, onGoBack, style }: Props) {
   return (
-    <HeaderSheet>
+    <HeaderSheet style={style}>
       <View style={styles.content}>
         {onGoBack ? <HeaderBackButton onPress={onGoBack} /> : null}
         <HeaderTitle>{title}</HeaderTitle>

src/components/Header/HeaderTitle.tsx

@@ -1,13 +1,16 @@
 import * as React from 'react';
-import { Text, StyleSheet, Platform, StyleProp, TextStyle } from 'react-native';
+import { StyleSheet, Platform } from 'react-native';
+import Animated from 'react-native-reanimated';
 
 type Props = {
   children: string;
-  style?: StyleProp<TextStyle>;
+  style?: React.ComponentProps<typeof Animated.Text>['style'];
 };
 
 export default function HeaderTitle({ children, style }: Props) {
-  return <Text style={[styles.title, style]}>{children}</Text>;
+  return (
+    <Animated.Text style={[styles.title, style]}>{children}</Animated.Text>
+  );
 }
 
 const styles = StyleSheet.create({
@@ -16,6 +19,7 @@ const styles = StyleSheet.create({
     marginHorizontal: 12,
     ...Platform.select({
       ios: {
+        textAlign: 'center',
         fontSize: 17,
         fontWeight: '600',
         color: 'rgba(0, 0, 0, .9)',