Show toast when pressing back button on channel screen (#4384)

* MM-24328: Show Press again to exit toast when back button on Channel screeen is pressed.

* Fix feedbacks.

* Handle back press only for the Channel screen.

* MM-24328: Add a back press handler to share activity.

* Update the toast message as Press back again to exit.

android/app/src/main/java/com/mattermost/share/ShareActivity.java

@@ -17,4 +17,9 @@ public class ShareActivity extends ReactActivity {
         MainApplication app = (MainApplication) this.getApplication();
         app.sharedExtensionIsOpened = true;
     }
+
+    @Override
+    public void onBackPressed() {
+        finish();
+    }
 }

app/screens/channel/channel.android.js

@@ -2,7 +2,7 @@
 // See LICENSE.txt for license information.
 
 import React from 'react';
-import {StyleSheet, View} from 'react-native';
+import {StyleSheet, View, BackHandler, ToastAndroid} from 'react-native';
 
 import {openMainSideMenu, openSettingsSideMenu} from '@actions/navigation';
 import LocalConfig from '@assets/config';
@@ -12,12 +12,15 @@ import NetworkIndicator from '@components/network_indicator';
 import PostDraft from '@components/post_draft';
 import {NavigationTypes} from '@constants';
 import EventEmitter from '@mm-redux/utils/event_emitter';
+import EphemeralStore from '@store/ephemeral_store';
 
 import ChannelNavBar from './channel_nav_bar';
 import ChannelPostList from './channel_post_list';
 
 import ChannelBase, {ClientUpgradeListener} from './channel_base';
 
+let backPressedCount = 0;
+
 export default class ChannelAndroid extends ChannelBase {
     openMainSidebar = () => {
         EventEmitter.emit(NavigationTypes.BLUR_POST_DRAFT);
@@ -29,6 +32,33 @@ export default class ChannelAndroid extends ChannelBase {
         openSettingsSideMenu();
     };
 
+    componentDidMount() {
+        super.componentDidMount();
+        BackHandler.addEventListener('hardwareBackPress', this.handleBackPress);
+    }
+
+    handleBackPress = () => {
+        if (!backPressedCount && EphemeralStore.getNavigationTopComponentId() === 'Channel') {
+            const {formatMessage} = this.context.intl;
+            backPressedCount++;
+            ToastAndroid.show(formatMessage({
+                id: 'mobile.android.back_handler_exit',
+                defaultMessage: 'Press back again to exit',
+            }), ToastAndroid.SHORT);
+            setTimeout(() => {
+                backPressedCount = 0;
+            }, 2000);
+            return true;
+        }
+        backPressedCount = 0;
+        return false;
+    };
+
+    componentWillUnmount() {
+        super.componentWillUnmount();
+        BackHandler.removeEventListener('hardwareBackPress', this.handleBackPress);
+    }
+
     render() {
         const {theme} = this.props;
         let component = this.renderLoadingOrFailedChannel();

assets/base/i18n/en.json

@@ -140,6 +140,7 @@
   "mobile.advanced_settings.timezone": "Timezone",
   "mobile.advanced_settings.title": "Advanced Settings",
   "mobile.alert_dialog.alertCancel": "Cancel",
+  "mobile.android.back_handler_exit": "Press back again to exit",
   "mobile.android.photos_permission_denied_description": "Upload photos to your Mattermost instance or save them to your device. Open Settings to grant Mattermost Read and Write access to your photo library.",
   "mobile.android.photos_permission_denied_title": "{applicationName} would like to access your photos",
   "mobile.android.videos_permission_denied_description": "Upload videos to your Mattermost instance or save them to your device. Open Settings to grant Mattermost Read and Write access to your video library.",