[change] call 'onLayout' when elements are resized

Uses ResizeObserver to monitor layout changes. Falls back to
window.onresize (with initial firing).

Fix #60
Close #848

packages/react-native-web/src/modules/applyLayout/index.js

@@ -9,6 +9,7 @@
 
 import { canUseDOM } from 'fbjs/lib/ExecutionEnvironment';
 import debounce from 'debounce';
+import findNodeHandle from '../../exports/findNodeHandle';
 
 const emptyObject = {};
 const registry = {};
@@ -16,22 +17,68 @@ const registry = {};
 let id = 1;
 const guid = () => `r-${id++}`;
 
+let resizeObserver;
 if (canUseDOM) {
-  const triggerAll = () => {
-    Object.keys(registry).forEach(key => {
-      const instance = registry[key];
-      instance._handleLayout();
+  if (typeof window.ResizeObserver !== 'undefined') {
+    resizeObserver = new window.ResizeObserver(entries => {
+      entries.forEach(({ target }) => {
+        const instance = registry[target._onLayoutId];
+        instance && instance._handleLayout();
+      });
     });
-  };
+  } else {
+    if (process.env.NODE_ENV !== 'production' && process.env.NODE_ENV !== 'test') {
+      console.warn(
+        'onLayout relies on ResizeObserver which is not supported by your browser. ' +
+          'Please include a polyfill, e.g., https://github.com/que-etc/resize-observer-polyfill. ' +
+          'Falling back to window.onresize.'
+      );
+    }
 
-  window.addEventListener('resize', debounce(triggerAll, 16), false);
+    const triggerAll = () => {
+      Object.keys(registry).forEach(key => {
+        const instance = registry[key];
+        instance._handleLayout();
+      });
+    };
+
+    window.addEventListener('resize', debounce(triggerAll, 16), false);
+  }
 }
 
+const observe = instance => {
+  const id = guid();
+  registry[id] = instance;
+
+  if (resizeObserver) {
+    const node = findNodeHandle(instance);
+    node._onLayoutId = id;
+    resizeObserver.observe(node);
+  } else {
+    const id = guid();
+    instance._onLayoutId = id;
+    instance._handleLayout();
+  }
+};
+
+const unobserve = instance => {
+  delete registry[instance._onLayoutId];
+  if (resizeObserver) {
+    const node = findNodeHandle(instance);
+    delete node._onLayoutId;
+    resizeObserver.unobserve(node);
+  } else {
+    delete instance._onLayoutId;
+  }
+};
+
 const safeOverride = (original, next) => {
   if (original) {
     return function prototypeOverride() {
-      original.call(this);
-      next.call(this);
+      /* eslint-disable prefer-rest-params */
+      original.call(this, arguments);
+      next.call(this, arguments);
+      /* eslint-enable prefer-rest-params */
     };
   }
   return next;
@@ -47,16 +94,20 @@ const applyLayout = Component => {
     function componentDidMount() {
       this._layoutState = emptyObject;
       this._isMounted = true;
-      this._onLayoutId = guid();
-      registry[this._onLayoutId] = this;
-      this._handleLayout();
+      observe(this);
     }
   );
 
   Component.prototype.componentDidUpdate = safeOverride(
     componentDidUpdate,
-    function componentDidUpdate() {
-      this._handleLayout();
+    function componentDidUpdate(prevProps) {
+      if (this.props.onLayout && !prevProps.onLayout) {
+        observe(this);
+      } else if (!this.props.onLayout && prevProps.onLayout) {
+        unobserve(this);
+      } else if (!resizeObserver) {
+        this._handleLayout();
+      }
     }
   );
 
@@ -64,7 +115,7 @@ const applyLayout = Component => {
     componentWillUnmount,
     function componentWillUnmount() {
       this._isMounted = false;
-      delete registry[this._onLayoutId];
+      unobserve(this);
     }
   );
 

website/guides/getting-started.md

@@ -2,8 +2,9 @@
 
 This guide will help you to use and test React Native for Web once it has been installed.
 
-Your application may need to polyfill `Promise`, `Object.assign`, and
-`Array.from` as necessary for your desired browser support.
+Your application may need to polyfill `Promise`, `Object.assign`, `Array.from`,
+and [`ResizeObserver`](https://github.com/que-etc/resize-observer-polyfill) as
+necessary for your desired browser support.
 
 ## Adding to a new web app
 

website/storybook/1-components/Text/TextScreen.js

@@ -132,13 +132,13 @@ const TextScreen = () => (
       <DocItem
         name="onLayout"
         typeInfo="?function"
-        description={
+        description={[
           <AppText>
             Invoked on mount and layout changes with{' '}
             <Code>{'{ nativeEvent: { layout: { x, y, width, height } } }'}</Code>, where{' '}
             <Code>x</Code> and <Code>y</Code> are the offsets from the parent node.
           </AppText>
-        }
+        ]}
       />
 
       <DocItem

website/storybook/1-components/View/ViewScreen.js

@@ -4,6 +4,7 @@
  * @flow
  */
 
+import PropOnLayout from './examples/PropOnLayout';
 import PropPointerEvents from './examples/PropPointerEvents';
 import transformExamples from './examples/transforms';
 import ZIndexExample from './examples/ZIndex';
@@ -132,6 +133,9 @@ const ViewScreen = () => (
             <Code>x</Code> and <Code>y</Code> are the offsets from the parent node.
           </AppText>
         }
+        example={{
+          render: () => <PropOnLayout />
+        }}
       />
 
       <DocItem

website/storybook/1-components/View/examples/PropOnLayout.js

@@ -0,0 +1,76 @@
+/**
+ * @flow
+ */
+
+import React from 'react';
+import { StyleSheet, Text, View } from 'react-native';
+
+const l1 = { width: '100%', paddingLeft: 0, paddingTop: 0 };
+const l2 = { width: '75%', paddingLeft: 10, paddingTop: 10 };
+
+export default class ViewOnLayoutExample extends React.Component {
+  state = {
+    layoutInfo: {}
+  };
+
+  componentDidMount() {
+    this._layout = l1;
+
+    this._interval = setInterval(() => {
+      if (this._ref) {
+        this._ref.setNativeProps({ style: this._layout });
+        this._layout = this._layout.width === '100%' ? l2 : l1;
+      }
+    }, 2000);
+  }
+
+  componentWillUnmount() {
+    clearInterval(this._interval);
+  }
+
+  render() {
+    const { x, y, width, height } = this.state.layoutInfo;
+    return (
+      <View style={styles.root}>
+        <View style={styles.left}>
+          <Text>x: {x}</Text>
+          <Text>y: {y}</Text>
+          <Text>width: {width}</Text>
+          <Text>height: {height}</Text>
+        </View>
+        <View style={styles.right}>
+          <View ref={this._setRef} style={styles.container}>
+            <View onLayout={this._handleLayout} style={styles.box} />
+          </View>
+        </View>
+      </View>
+    );
+  }
+
+  _handleLayout = ({ nativeEvent }) => {
+    this.setState(() => ({ layoutInfo: nativeEvent.layout }));
+  };
+
+  _setRef = component => {
+    this._ref = component;
+  };
+}
+
+const styles = StyleSheet.create({
+  root: {
+    flexDirection: 'row'
+  },
+  container: {
+    height: 50
+  },
+  left: {
+    width: 100
+  },
+  right: {
+    flex: 1
+  },
+  box: {
+    backgroundColor: '#eee',
+    flex: 1
+  }
+});

website/storybook/1-components/View/examples/PropPointerEvents.js

@@ -18,7 +18,7 @@ const Box = ({ pointerEvents }) => (
   </TouchableHighlight>
 );
 
-const ViewStyleExample = () => (
+const ViewPointerEventsExample = () => (
   <View pointerEvents="box-none">
     <View pointerEvents="box-none" style={styles.container}>
       <Box pointerEvents="none" />
@@ -43,4 +43,4 @@ const styles = StyleSheet.create({
     borderStyle: 'solid'
   }
 });
-export default ViewStyleExample;
+export default ViewPointerEventsExample;