custom back button handler

Summary:sometimes it is nessesary to handle back button
specifically for component, by changing its state.
 For ex. exit from edit mode.
Closes https://github.com/facebook/react-native/pull/5062

Differential Revision: D3084590

Pulled By: ericvicenti

fb-gh-sync-id: 13a4ea1d64ce725daa5d3af0d629a0c132a3f3d5
shipit-source-id: 13a4ea1d64ce725daa5d3af0d629a0c132a3f3d5

Examples/UIExplorer/BackAndroidExample.js

@@ -0,0 +1,66 @@
+/**
+ * The examples provided by Facebook are for non-commercial testing and
+ * evaluation purposes only.
+ *
+ * Facebook reserves all rights not expressly granted.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS
+ * OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NON INFRINGEMENT. IN NO EVENT SHALL
+ * FACEBOOK BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN
+ * AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
+ * CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
+ *
+ */
+
+'use strict';
+
+var React = require('react-native');
+var {
+  Text,
+  View,
+  BackAndroid,
+} = React;
+
+var BackAndroidExample = React.createClass({
+
+  getInitialState: function() {
+    return {
+      defaultBackHandler: false
+    };
+  },
+
+  componentDidMount: function() {
+    BackAndroid.addEventListener('hardwareBackPress', this._handleBackButton);
+  },
+
+  componentWillUnmount: function() {
+    BackAndroid.removeEventListener('hardwareBackPress', this._handleBackButton);
+  },
+
+  _handleBackButton: function() {
+    if (!this.state.defaultBackHandler) {
+      this.setState({defaultBackHandler: true});
+      return true;
+    }
+
+    return false;
+  },
+
+  render: function() {
+    return (
+      <View>
+        <Text>{this.state.defaultBackHandler ? 'Ok, I\'ll quit.' : 'I won\'t quit.'}</Text>
+      </View>
+    );
+  },
+});
+
+exports.title = 'BackAndroid';
+exports.description = 'Custom back button handler';
+exports.examples = [
+  {
+    title: 'Custom back button handler',
+    render(): ReactElement { return <BackAndroidExample />; }
+  }
+];

Examples/UIExplorer/UIExplorerList.android.js

@@ -102,6 +102,10 @@ const APIExamples = [
     key: 'AppStateExample',
     module: require('./AppStateExample'),
   },
+  {
+    key: 'BackAndroidExample',
+    module: require('./BackAndroidExample'),
+  },
   {
     key: 'BorderExample',
     module: require('./BorderExample'),

Libraries/Utilities/BackAndroid.android.js

@@ -20,17 +20,19 @@ type BackPressEventName = $Enum<{
   backPress: string;
 }>;
 
-var _backPressSubscriptions = new Set();
+var _backPressSubscriptions = [];
 
 RCTDeviceEventEmitter.addListener(DEVICE_BACK_EVENT, function() {
-  var backPressSubscriptions = new Set(_backPressSubscriptions);
+  var propagate = true;
-  var invokeDefault = true;
+  for (var i = _backPressSubscriptions.length - 1; i >= 0; i--) {
-  backPressSubscriptions.forEach((subscription) => {
+    var subscription = _backPressSubscriptions[i];
     if (subscription()) {
-      invokeDefault = false;
+      propagate = false;
+      break;
     }
-  });
+  }
-  if (invokeDefault) {
+
+  if (propagate) {
     BackAndroid.exitApp();
   }
 });
@@ -60,18 +62,18 @@ var BackAndroid = {
   addEventListener: function (
     eventName: BackPressEventName,
     handler: Function
-  ): {remove: () => void} {
+  ): void {
-    _backPressSubscriptions.add(handler);
+    _backPressSubscriptions.push(handler);
-    return {
-      remove: () => BackAndroid.removeEventListener(eventName, handler),
-    };
   },
 
   removeEventListener: function(
     eventName: BackPressEventName,
     handler: Function
   ): void {
-    _backPressSubscriptions.delete(handler);
+    var index = _backPressSubscriptions.indexOf(handler);
+    if (index !== -1) {
+      _backPressSubscriptions.splice(index, 1);
+    }
   },
 
 };