2015-09-03 16:06:50 +00:00
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# 在線/離線事件偵測
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我們可以在渲染引擎 (renderer) 的行程裡用標準的 HTML5 API 來實作在線與離線事件的偵測。
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請參考以下範例:
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_main.js_
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```javascript
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var app = require('app');
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var BrowserWindow = require('browser-window');
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var onlineStatusWindow;
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app.on('ready', function() {
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onlineStatusWindow = new BrowserWindow({ width: 0, height: 0, show: false });
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2015-11-24 12:02:14 +00:00
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onlineStatusWindow.loadURL('file://' + __dirname + '/online-status.html');
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2015-09-03 16:06:50 +00:00
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});
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```
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_online-status.html_
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```html
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<!DOCTYPE html>
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<html>
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<body>
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<script>
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var alertOnlineStatus = function() {
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window.alert(navigator.onLine ? 'online' : 'offline');
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};
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window.addEventListener('online', alertOnlineStatus);
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window.addEventListener('offline', alertOnlineStatus);
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alertOnlineStatus();
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</script>
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</body>
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</html>
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```
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您也許有時候也會有想要在主行程裡回應這些事件的情況。然而，在主行程裡並沒有 `navigator` 這個物件，因此不能直接地偵測這些事件。
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但我們可以使用 Electron 所提供的跨行程 (inter-process) 溝通的工具，事件就可以被傳送到主程序內並做您所需的處理。
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請參考以下範例:
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_main.js_
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```javascript
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var app = require('app');
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var ipc = require('ipc');
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var BrowserWindow = require('browser-window');
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var onlineStatusWindow;
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app.on('ready', function() {
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onlineStatusWindow = new BrowserWindow({ width: 0, height: 0, show: false });
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2015-11-24 12:02:14 +00:00
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onlineStatusWindow.loadURL('file://' + __dirname + '/online-status.html');
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2015-09-03 16:06:50 +00:00
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});
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ipc.on('online-status-changed', function(event, status) {
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console.log(status);
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});
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```
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_online-status.html_
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```html
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<!DOCTYPE html>
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<html>
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<body>
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<script>
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var ipc = require('ipc');
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var updateOnlineStatus = function() {
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ipc.send('online-status-changed', navigator.onLine ? 'online' : 'offline');
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};
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window.addEventListener('online', updateOnlineStatus);
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window.addEventListener('offline', updateOnlineStatus);
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updateOnlineStatus();
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</script>
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</body>
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</html>
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```
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