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| 1 <h1 id="lab_6_lifecycle">Lab 6 - Lifecycle</h1> |
| 2 |
| 3 <p>Like everything in this world, apps have a lifecycle. They are installed, la
unched, restarted, suspended when the system needs to free up resources and unin
stalled. This lab will show you the basics of the Chrome app lifecycle and how
its heart, the event page (aka background script), is used.</p> |
| 4 |
| 5 <h2 id="you_should_also_read">You should also read</h2> |
| 6 |
| 7 <p><a href="http://developer.chrome.com/apps/app_lifecycle.html">Manage App Life
cycle</a> in Chrome app docs</p> |
| 8 |
| 9 <h2 id="the_event_page">The event page</h2> |
| 10 |
| 11 <p>The event page is one of the most important pieces of a Chrome app. It's
responsible for what gets launched, when, and how. |
| 12 For example, if your app is an instant messenger, you might want your event page
to only show a UI when there is a new notification.</p> |
| 13 |
| 14 <p>For simpler apps, the event page listens to the app lifecycle events and reac
ts appropriately. |
| 15 There are two important lifecycle events, <a href="http://developer.chrome.com/t
runk/apps/app.runtime.html#event-onLaunched">onLaunched</a> and <a href="http://
developer.chrome.com/trunk/apps/app.runtime.html#event-onRestarted">onRestarted<
/a>.</p> |
| 16 |
| 17 <h2 id="the_onlaunched_event_and_the_chrome_app_window_create_method">The onLaun
ched event and the chrome.app.window.create method</h2> |
| 18 |
| 19 <p><a href="http://developer.chrome.com/apps/app.runtime.html#event-onLaunched">
onLaunched</a> is the most important event. It fires when the user clicks on you
r app's icon with the intent of launching it. For most simpler apps, the eve
nt page will listen for this event and open a window when it fires. See our <a h
ref="https://github.com/GoogleChrome/chrome-app-codelab/blob/master/lab6_lifecyc
le/angularjs/main.js">main.js</a> for the most common usage.</p> |
| 20 |
| 21 <h3 id="windows_with_ids">Windows with IDs</h3> |
| 22 |
| 23 <p>The <a href="http://developer.chrome.com/trunk/apps/app.window.html#method-cr
eate">chrome.app.window.create</a> method can associate an ID to the window bein
g opened. Currently, the most interesting use for this is to restore a window
9;s width, height and location and its associated Developer Tools window, if ope
ned, when the app is launched. </p> |
| 24 |
| 25 <p>Execute your app as it is now, move and resize the window, close and restart
it. The app will reopen in the original location, right? Now add a property <cod
e>id</code> to the <a href="https://github.com/GoogleChrome/chrome-app-codelab/b
lob/master/lab6_lifecycle/angularjs/main.js">main.js</a>, reload the app and tes
t again:</p> |
| 26 |
| 27 <pre><code><pre> |
| 28 chrome.app.runtime.onLaunched.addListener(function() { |
| 29 chrome.app.window.create('index.html', |
| 30 {id: 'mainwindow', width: 500, height: 309}); |
| 31 }); |
| 32 </pre></code></pre> |
| 33 |
| 34 If your application requires, you can open more than one window. |
| 35 |
| 36 <h2 id="the_onrestarted_event">The onRestarted event</h2> |
| 37 |
| 38 The <a href="http://developer.chrome.com/apps/app.runtime.html#event-onRestarted
">onRestarted</a> event is not as essential as <code>onLaunched</code>, but it m
ight be relevant to certain types of apps. |
| 39 This event is executed when the app is restarted, for example, when Chrome quits
, restarts, and the app is launched again. |
| 40 You can use this event to restore a transient state. |
| 41 |
| 42 For example, if your app has a form with several fields, you won't always wa
nt to save the partial form while the user is typing. |
| 43 If the user quits the app on purpose, she might not be interested keeping the pa
rtial data. |
| 44 If the Chrome runtime restarted for some reason other than by a user's inten
tion, the user will want that data when the app is restarted. |
| 45 |
| 46 Let's change our code to save the Todo input field in <a href="http://develo
per.chrome.com/trunk/apps/storage.html">chrome.storage.local</a> as the user typ
es, only restoring it if the <code>onRestarted</code> event is triggered. |
| 47 |
| 48 <p class="note"><b>Note:</b> We learned about <code>chrome.storage.sync</code>
before, but <a href="http://developer.chrome.com/trunk/apps/storage.html#using-s
ync">chrome.storage.local</a> wasn't mentioned until now. Both have exactly
the same syntax, but the semantics of <code>chrome.storage.local</code> is, as t
he name says, completely local. |
| 49 There's no attempt to synchronize or to save the data in the cloud.</p> |
| 50 |
| 51 <ul> |
| 52 <li>Event page: <a href="https://github.com/GoogleChrome/chrome-app-codelab/blob
/master/lab6_lifecycle/angularjs/main.js">main.js</a> |
| 53 <pre> |
| 54 chrome.app.runtime.onLaunched.addListener(function() { |
| 55 // normal launch initiated by the user, let's start clean. |
| 56 // note that this is not related to the persistent state, which is |
| 57 // appropriately handled in the window code. |
| 58 runApp(false); |
| 59 }); |
| 60 |
| 61 chrome.app.runtime.onRestarted.addListener(function() { |
| 62 // if restarted, try to get the transient saved state |
| 63 runApp(true); |
| 64 }); |
| 65 |
| 66 function runApp(readInitialState) { |
| 67 chrome.app.window.create('index.html', |
| 68 {id: 'mainwindow', width: 500, height: 309}, |
| 69 // the create callback gets a reference to the AppWindow obj |
| 70 function(win) { |
| 71 // when the callback is executed, the DOM is loaded but no script was |
| 72 // loaded yet. So, let's attach to the load event. |
| 73 win.contentWindow.addEventListener('load', function() { |
| 74 if (readInitialState) { |
| 75 win.contentWindow.setInitialState(); |
| 76 } else { |
| 77 win.contentWindow.clearInitialState(); |
| 78 } |
| 79 }); |
| 80 }); |
| 81 } |
| 82 </pre></li><li>Controller: add to existing <a href="https://github.com/GoogleChr
ome/chrome-app-codelab/blob/master/lab6_lifecycle/angularjs/controller.js">contr
oller.js</a> |
| 83 <pre> |
| 84 var newTodoInput = null; |
| 85 |
| 86 var clearInitialState = function() { |
| 87 chrome.storage.local.set({'newtodo': null}); |
| 88 } |
| 89 |
| 90 var setInitialState = function() { |
| 91 chrome.storage.local.get('newtodo', function(data) { |
| 92 if (newTodoInput && data && data.newtodo) { |
| 93 newTodoInput.value = data.newtodo; |
| 94 newTodoInput.focus(); |
| 95 } |
| 96 }); |
| 97 } |
| 98 |
| 99 window.addEventListener('load', function() { |
| 100 var saveTransientState = function() { |
| 101 chrome.storage.local.set({'newtodo': newTodoInput.value}); |
| 102 }; |
| 103 newTodoInput = document.querySelector('input[type="text"]'); |
| 104 newTodoInput.addEventListener('keypress' , function() { |
| 105 saveTransientState();<br> |
| 106 }) |
| 107 }) |
| 108 </pre></p></li><li><p>Save the changes by reloading the app: open the app, right
-click and select Reload.</p></li> |
| 109 </ul> |
| 110 |
| 111 <p>If Chrome and the app shuts down for any reason (other than a user-gesture),
the <code>onRestarted</code> event is fired. |
| 112 Any text entered in the input field (but not yet saved as a Todo item) will reap
pear when Chrome and the app are reopened.</p> |
| 113 |
| 114 <p class="note"><b>Note:</b> If you get stuck and want to see the app in action
, go to <code>chrome://extensions</code>, |
| 115 load the unpacked <a href="app_codelab6_lifecycle.html">lab6_lifecycle</a>, and
launch the app from a new tab.</p> |
| 116 |
| 117 <h1 id="takeaways_">Takeaways:</h1> |
| 118 |
| 119 <ul> |
| 120 <li>The event page may continue to run even when your windows are closed. You ca
n move logic that is shared among windows to the event page, as we will see in <
a href="app_codelab9_multipleviews.html">lab9</a>.</li> |
| 121 </ul> |
| 122 |
| 123 <h1 id="what_39_s_next_">What's next?</h1> |
| 124 |
| 125 <p>In <a href="app_codelab7_useridentification.html">lab7_useridentification</a>
, |
| 126 you will learn how to identify users and use OAuth2.0 to access Google and other
third party services.</p> |
| 127 |
| 128 <p class="note"><b>Note:</b> The <a href="http://developer.chrome.com/trunk/app
s/app_identity.html">identify API</a> covered in lab 7 is still experimental.</p
> |
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