Fixed confirmExit for Electron apps.

The previous implementation did not work because the window was unloaded
before the dialog could be opened.

This implementation gets around some… unusual behaviour of Electron's
beforeunload event by using the will-prevent-unload WebContents event.

Signed-off-by: Matthew Gordon <matthew.gordon@arm.com>

dev-packages/application-manager/src/generator/frontend-generator.ts

@@ -125,7 +125,7 @@ process.env.LC_NUMERIC = 'C';
 const electron = require('electron');
 const { join, resolve } = require('path');
 const { fork } = require('child_process');
-const { app, shell, BrowserWindow, ipcMain, Menu } = electron;
+const { app, dialog, shell, BrowserWindow, ipcMain, Menu } = electron;
 
 const applicationName = \`${this.pck.props.frontend.config.applicationName}\`;
 const isSingleInstance = ${this.pck.props.backend.config.singleInstance === true ? 'true' : 'false'};
@@ -140,36 +140,6 @@ const nativeKeymap = require('native-keymap');
 const Storage = require('electron-store');
 const electronStore = new Storage();
 
-let canPreventStop = true;
-const windows = [];
-
-app.on('before-quit', async event => {
-    if (canPreventStop) {
-        // Pause the stop.
-        event.preventDefault();
-        let preventStop = false;
-        // Ask all opened windows whether they want to prevent the \`close\` event or not.
-        for (const window of windows) {
-            if (!preventStop) {
-                window.webContents.send('prevent-stop-request');
-                const preventStopPerWindow = await new Promise((resolve) => {
-                    ipcMain.once('prevent-stop-response', (_, arg) => {
-                        if (!!arg && 'preventStop' in arg && typeof arg.preventStop === 'boolean') {
-                            resolve(arg.preventStop);
-                        }
-                    })
-                });
-                if (preventStopPerWindow) {
-                    preventStop = true;
-                }
-            }
-        }
-        if (!preventStop) {
-            canPreventStop = false;
-            app.quit();
-        }
-    }
-});
 app.on('ready', () => {
     const { screen } = electron;
 
@@ -250,13 +220,20 @@ app.on('ready', () => {
         newWindow.on('close', saveWindowState);
         newWindow.on('resize', saveWindowStateDelayed);
         newWindow.on('move', saveWindowStateDelayed);
-        newWindow.on('closed', () => {
-            const index = windows.indexOf(newWindow);
-            if (index !== -1) {
-                windows.splice(index, 1);
-            }
-            if (windows.length === 0) {
-                app.quit();
+
+        // Fired when a beforeunload handler tries to prevent the page unloading
+        newWindow.webContents.on('will-prevent-unload', event => {
+            const preventStop = 0 !== dialog.showMessageBox(newWindow, {
+                type: 'question',
+                buttons: ['Yes', 'No'],
+                title: 'Confirm',
+                message: 'Are you sure you want to quit?',
+                detail: 'Any unsaved changes will not be saved.'
+            });
+
+            if (!preventStop) {
+                // This ignores the beforeunload callback, allowing the page to unload
+                event.preventDefault();
             }
         });
 
@@ -274,7 +251,6 @@ app.on('ready', () => {
         if (!!theUrl) {
             newWindow.loadURL(theUrl);
         }
-        windows.push(newWindow);
         return newWindow;
     }
 

packages/core/package.json

@@ -62,9 +62,6 @@
       "frontend": "lib/browser/keyboard/browser-keyboard-module",
       "frontendElectron": "lib/electron-browser/keyboard/electron-keyboard-module",
       "backendElectron": "lib/electron-node/keyboard/electron-backend-keyboard-module"
-    },
-    {
-      "frontendElectron": "lib/electron-browser/shutdown-hook/electron-shutdown-hook-module"
     }
   ],
   "keywords": [

packages/core/src/browser/window/default-window-service.ts

@@ -36,9 +36,7 @@ export class DefaultWindowService implements WindowService, FrontendApplicationC
         this.frontendApplication = app;
         window.addEventListener('beforeunload', event => {
             if (!this.canUnload()) {
-                event.returnValue = '';
-                event.preventDefault();
-                return '';
+                return this.preventUnload(event);
             }
         });
     }
@@ -66,4 +64,14 @@ export class DefaultWindowService implements WindowService, FrontendApplicationC
         return confirmExit !== 'always';
     }
 
+    /**
+     * Ask the user to confirm if they want to unload the window. Prevent it if they do not.
+     * @param event The beforeunload event
+     */
+    protected preventUnload(event: BeforeUnloadEvent): string | void {
+        event.returnValue = '';
+        event.preventDefault();
+        return '';
+    }
+
 }

packages/core/src/electron-browser/window/electron-window-service.ts

@@ -17,20 +17,11 @@
 import { injectable } from 'inversify';
 import { ipcRenderer } from 'electron';
 import { NewWindowOptions } from '../../browser/window/window-service';
-import { FrontendApplication } from '../../browser/frontend-application';
 import { DefaultWindowService } from '../../browser/window/default-window-service';
 
 @injectable()
 export class ElectronWindowService extends DefaultWindowService {
 
-    onStart(app: FrontendApplication): void {
-        this.frontendApplication = app;
-        // We do not want to add a `beforeunload` listener to the `window`.
-        // Why? Because by the time we get into the unload handler, it is already too late. Our application has quit.
-        // _Emitted when the `window` is going to be closed. It's emitted before the `beforeunload` and `unload` event of the DOM._
-        // https://github.com/electron/electron/blob/master/docs/api/browser-window.md#event-close
-    }
-
     openNewWindow(url: string, { external }: NewWindowOptions = {}): undefined {
         if (external) {
             ipcRenderer.send('open-external', url);
@@ -40,4 +31,9 @@ export class ElectronWindowService extends DefaultWindowService {
         return undefined;
     }
 
+    protected preventUnload(event: BeforeUnloadEvent): string | void {
+        // The user will be shown a confirmation dialog by the will-prevent-unload handler in the Electron main script
+        event.returnValue = false;
+    }
+
 }