1page.title=Remembering Your User 2parent.title=Remembering and Authenticating Users 3parent.link=index.html 4 5trainingnavtop=true 6next.title=Authenticating to OAuth2 Services 7next.link=authenticate.html 8 9@jd:body 10 11 12<div id="tb-wrapper"> 13 <div id="tb"> 14<h2>This lesson teaches you to</h2> 15<ol> 16 <li><a href="#ForYou">Determine if AccountManager for You</a></li> 17 <li><a href="#TaskTwo">Decide What Type of Account to Use</a></li> 18 <li><a href="#GetPermission">Request GET_ACCOUNT permission</a></li> 19 <li><a href="#TaskFive">Query AccountManager for a List of Accounts</a></li> 20 <li><a href="#IdentifyUser">Use the Account Object to Personalize Your App</a></li> 21 <li><a href="#IdIsEnough">Decide Whether an Account Name is Enough</a></li> 22</ol> 23 </div> 24</div> 25 26 27<p>Everyone likes it when you remember their name. One of the simplest, most 28effective things you can do to make your app more lovable is to remember who 29your user is—especially when the user upgrades to a new device or starts carrying 30a tablet as well as a phone. But how do you know who your user is? And how do 31you recognize them on a new device?</p> 32 33<p>For many applications, the answer is the {@link android.accounts.AccountManager} APIs. With the 34user's permission, you can use Account Manager to fetch the account names 35that the user has stored on their device.</p> 36 37<p>Integration with the user's accounts allows you to do a variety of things such as:</p> 38<ul> 39<li>Auto-fill forms with the user's email address.</li> 40<li>Retrieve an ID that is tied to a user, not the device.</li> 41</ul> 42 43 44<h2 id="ForYou">Determine if AccountManager for You</h2> 45 46<p>Applications typically try to remember the user using one of three techniques:</p> 47<ol type="a"> 48<li>Ask the user to type in a username </li> 49<li>Retrieve a unique device ID to remember the device</li> 50<li>Retrieve a built-in account from {@link android.accounts.AccountManager}</li> 51</ol> 52 53<p>Option (a) is problematic. First, asking the user to type something before 54entering your app will automatically make your app less appealing. Second, 55there's no guarantee that the username chosen will be unique. </p> 56 57<p>Option (b) is less onerous for the user, but it's 58<a href="http://android-developers.blogspot.com/2011/03/identifying-app-installations.html">tricky 59to get right</a>. More 60importantly, it only allows you to remember the user on one device. Imagine the 61frustration of someone who upgrades to a shiny new device, only to find that 62your app no longer remembers them.</p> 63 64<p>Option (c) is the preferred technique. Account Manager allows you to get 65information about the accounts that are stored on the user's device. As we'll 66see in this lesson, using Account Manager lets you remember your user, no matter 67how many devices the user may own, by adding just a couple of extra taps to your 68UI.</p> 69 70 71<h2 id="TaskTwo">Decide What Type of Account to Use</h2> 72 73<p>Android devices can store multiple accounts from many different providers. 74When you query {@link android.accounts.AccountManager} for account names, you can choose to filter 75by 76account type. The account type is a string that uniquely identifies the entity 77that issued the account. For instance, Google accounts have type "com.google," 78while Twitter uses "com.twitter.android.auth.login."</p> 79 80 81<h2 id="GetPermission">Request GET_ACCOUNT permission</h2> 82 83<p>In order to get a list of accounts on the device, your app needs the {@link 84android.Manifest.permission#GET_ACCOUNTS} 85permission. Add a <a href="{@docRoot}guide/topics/manifest/uses-permission-element.html">{@code 86<uses-permission>}</a> tag in your manifest file to request 87this permission:</p> 88 89<pre> 90<manifest ... > 91 <uses-permission android:name="android.permission.GET_ACCOUNTS" /> 92 ... 93</manifest> 94</pre> 95 96 97<h2 id="TaskFive">Query AccountManager for a List of Accounts</h2> 98 99<p>Once you decide what account type you're interested in, you need to query for accounts of that 100type. Get an instance of {@link android.accounts.AccountManager} by calling {@link 101android.accounts.AccountManager#get(android.content.Context) AccountManager.get()}. Then use that 102instance to call {@link android.accounts.AccountManager#getAccountsByType(java.lang.String) 103getAccountsByType()}.</p> 104 105<pre> 106AccountManager am = AccountManager.get(this); // "this" references the current Context 107 108Account[] accounts = am.getAccountsByType("com.google"); 109</pre> 110 111<p>This returns an array of {@link android.accounts.Account} objects. If there's more than one 112{@link android.accounts.Account} in 113the array, you should present a dialog asking the user to select one.</p> 114 115 116<h2 id="IdentifyUser">Use the Account Object to Personalize Your App</h2> 117 118<p>The {@link android.accounts.Account} object contains an account name, which for Google accounts 119is an 120email address. You can use this information in several different ways, such as: 121<ul> 122 <li> As suggestions in forms, so the user doesn't need to input account information by 123hand.</li> 124 <li> As a key into your own online database of usage and personalization information.</li> 125</ul> 126</p> 127 128 129<h2 id="IdIsEnough">Decide Whether an Account Name is Enough</h2> 130 131<p>An account name is a good way to remember the user, but the {@link android.accounts.Account} 132object by 133itself doesn't protect your data or give you access to anything besides the user's account name. If your app 134needs to allow the user to go online to access private data, you'll need something stronger: authentication. 135The next lesson explains how to authenticate to existing online services. The lesson after that 136deals with writing a custom authenticator so that you can install your own 137account types.</p> 138