1 page.title=Sending the User to Another App 2 parent.title=Interacting with Other Apps 3 parent.link=index.html 4 5 trainingnavtop=true 6 next.title=Getting a Result from an Activity 7 next.link=result.html 8 9 @jd:body 10 11 12 <div id="tb-wrapper"> 13 <div id="tb"> 14 15 <h2>This lesson teaches you to</h2> 16 <ol> 17 <li><a href="#Build">Build an Implicit Intent</a></li> 18 <li><a href="#Verify">Verify There is an App to Receive the Intent</a></li> 19 <li><a href="#StartActivity">Start an Activity with the Intent</a></li> 20 <li><a href="#AppChooser">Show an App Chooser</a></li> 21 </ol> 22 23 <h2>You should also read</h2> 24 <ul> 25 <li><a href="{@docRoot}training/sharing/index.html">Sharing Content</a></li> 26 </ul> 27 28 </div> 29 </div> 30 31 <p>One of Android's most important features is an app's ability to send the user to another app 32 based on an "action" it would like to perform. For example, if 33 your app has the address of a business that you'd like to show on a map, you don't have to build 34 an activity in your app that shows a map. Instead, you can create a request to view the address 35 using an {@link android.content.Intent}. The Android system then starts an app that's able to show 36 the address on a map.</p> 37 38 <p>As explained in the first class, <a href="{@docRoot}training/basics/firstapp/index.html">Building 39 Your First App</a>, you must use intents to navigate between activities in your own app. You 40 generally do so with an <em>explicit intent</em>, which defines the exact class name of the 41 component you want to start. However, when you want to have a separate app perform an action, such 42 as "view a map," you must use an <em>implicit intent</em>.</p> 43 44 <p>This lesson shows you how to create an implicit intent for a particular action, and how to use it 45 to start an activity that performs the action in another app.</p> 46 47 48 49 <h2 id="Build">Build an Implicit Intent</h2> 50 51 <p>Implicit intents do not declare the class name of the component to start, but instead declare an 52 action to perform. The action specifies the thing you want to do, such as <em>view</em>, 53 <em>edit</em>, <em>send</em>, or <em>get</em> something. Intents often also include data associated 54 with the action, such as the address you want to view, or the email message you want to send. 55 Depending on the intent you want to create, the data might be a {@link android.net.Uri}, 56 one of several other data types, or the intent might not need data at all.</p> 57 58 <p>If your data is a {@link android.net.Uri}, there's a simple {@link 59 android.content.Intent#Intent(String,Uri) Intent()} constructor you can use define the action and 60 data.</p> 61 62 <p>For example, here's how to create an intent to initiate a phone call using the {@link 63 android.net.Uri} data to specify the telephone number:</p> 64 65 <pre> 66 Uri number = Uri.parse("tel:5551234"); 67 Intent callIntent = new Intent(Intent.ACTION_DIAL, number); 68 </pre> 69 70 <p>When your app invokes this intent by calling {@link android.app.Activity#startActivity 71 startActivity()}, the Phone app initiates a call to the given phone number.</p> 72 73 <p>Here are a couple other intents and their action and {@link android.net.Uri} data 74 pairs:</p> 75 76 <ul> 77 <li>View a map: 78 <pre> 79 // Map point based on address 80 Uri location = Uri.parse("geo:0,0?q=1600+Amphitheatre+Parkway,+Mountain+View,+California"); 81 // Or map point based on latitude/longitude 82 // Uri location = Uri.parse("geo:37.422219,-122.08364?z=14"); // z param is zoom level 83 Intent mapIntent = new Intent(Intent.ACTION_VIEW, location); 84 </pre> 85 </li> 86 <li>View a web page: 87 <pre> 88 Uri webpage = Uri.parse("http://www.android.com"); 89 Intent webIntent = new Intent(Intent.ACTION_VIEW, webpage); 90 </pre> 91 </li> 92 </ul> 93 94 <p>Other kinds of implicit intents require "extra" data that provide different data types, 95 such as a string. You can add one or more pieces of extra data using the various {@link 96 android.content.Intent#putExtra(String,String) putExtra()} methods.</p> 97 98 <p>By default, the system determines the appropriate MIME type required by an intent based on the 99 {@link android.net.Uri} data that's included. If you don't include a {@link android.net.Uri} in the 100 intent, you should usually use {@link android.content.Intent#setType setType()} to specify the type 101 of data associated with the intent. Setting the MIME type further specifies which kinds of 102 activities should receive the intent.</p> 103 104 <p>Here are some more intents that add extra data to specify the desired action:</p> 105 106 <ul> 107 <li>Send an email with an attachment: 108 <pre> 109 Intent emailIntent = new Intent(Intent.ACTION_SEND); 110 // The intent does not have a URI, so declare the "text/plain" MIME type 111 emailIntent.setType(HTTP.PLAIN_TEXT_TYPE); 112 emailIntent.putExtra(Intent.EXTRA_EMAIL, new String[] {"jon (a] example.com"}); // recipients 113 emailIntent.putExtra(Intent.EXTRA_SUBJECT, "Email subject"); 114 emailIntent.putExtra(Intent.EXTRA_TEXT, "Email message text"); 115 emailIntent.putExtra(Intent.EXTRA_STREAM, Uri.parse("content://path/to/email/attachment")); 116 // You can also attach multiple items by passing an ArrayList of Uris 117 </pre> 118 </li> 119 <li>Create a calendar event: 120 <pre> 121 Intent calendarIntent = new Intent(Intent.ACTION_INSERT, Events.CONTENT_URI); 122 Calendar beginTime = Calendar.getInstance().set(2012, 0, 19, 7, 30); 123 Calendar endTime = Calendar.getInstance().set(2012, 0, 19, 10, 30); 124 calendarIntent.putExtra(CalendarContract.EXTRA_EVENT_BEGIN_TIME, beginTime.getTimeInMillis()); 125 calendarIntent.putExtra(CalendarContract.EXTRA_EVENT_END_TIME, endTime.getTimeInMillis()); 126 calendarIntent.putExtra(Events.TITLE, "Ninja class"); 127 calendarIntent.putExtra(Events.EVENT_LOCATION, "Secret dojo"); 128 </pre> 129 <p class="note"><strong>Note:</strong> This intent for a calendar event is supported only with API 130 level 14 and higher.</p> 131 </li> 132 </ul> 133 134 <p class="note"><strong>Note:</strong> It's important that you define your {@link 135 android.content.Intent} to be as specific as possible. For example, if you want to display an image 136 using the {@link android.content.Intent#ACTION_VIEW} intent, you should specify a MIME type of 137 {@code image/*}. This prevents apps that can "view" other types of data (like a map app) from being 138 triggered by the intent.</p> 139 140 141 142 <h2 id="Verify">Verify There is an App to Receive the Intent</h2> 143 144 <p>Although the Android platform guarantees that certain intents will resolve to one of the 145 built-in apps (such as the Phone, Email, or Calendar app), you should always include a 146 verification step before invoking an intent.</p> 147 148 <p class="caution"><strong>Caution:</strong> If you invoke an intent and there is no app 149 available on the device that can handle the intent, your app will crash.</p> 150 151 <p>To verify there is an activity available that can respond to the intent, call {@link 152 android.content.pm.PackageManager#queryIntentActivities queryIntentActivities()} to get a list 153 of activities capable of handling your {@link android.content.Intent}. If the returned {@link 154 java.util.List} is not empty, you can safely use the intent. For example:</p> 155 156 <pre> 157 PackageManager packageManager = {@link android.content.Context#getPackageManager()}; 158 List<ResolveInfo> activities = packageManager.queryIntentActivities(intent, 0); 159 boolean isIntentSafe = activities.size() > 0; 160 </pre> 161 162 <p>If <code>isIntentSafe</code> is <code>true</code>, then at least one app will respond to 163 the intent. If it is <code>false</code>, then there aren't any apps to handle the intent.</p> 164 165 <p class="note"><strong>Note:</strong> You should perform this check when your activity first 166 starts in case you need to disable the feature that uses the intent before the user attempts to use 167 it. If you know of a specific app that can handle the intent, you can also provide a link for the 168 user to download the app (see how to <a 169 href="{@docRoot}distribute/googleplay/promote/linking.html">link to your product on Google 170 Play</a>).</p> 171 172 173 <h2 id="StartActivity">Start an Activity with the Intent</h2> 174 175 <div class="figure" style="width:200px"> 176 <img src="{@docRoot}images/training/basics/intents-choice.png" alt="" /> 177 <p class="img-caption"><strong>Figure 1.</strong> Example of the selection dialog that appears 178 when more than one app can handle an intent.</p> 179 </div> 180 181 <p>Once you have created your {@link android.content.Intent} and set the extra info, call {@link 182 android.app.Activity#startActivity startActivity()} to send it to the system. If the system 183 identifies more than one activity that can handle the intent, it displays a dialog for the user to 184 select which app to use, as shown in figure 1. If there is only one activity that handles the 185 intent, the system immediately starts it.</p> 186 187 <pre> 188 startActivity(intent); 189 </pre> 190 191 <p>Here's a complete example that shows how to create an intent to view a map, verify that an 192 app exists to handle the intent, then start it:</p> 193 194 <pre> 195 // Build the intent 196 Uri location = Uri.parse("geo:0,0?q=1600+Amphitheatre+Parkway,+Mountain+View,+California"); 197 Intent mapIntent = new Intent(Intent.ACTION_VIEW, location); 198 199 // Verify it resolves 200 PackageManager packageManager = {@link android.content.Context#getPackageManager()}; 201 List<ResolveInfo> activities = packageManager.queryIntentActivities(mapIntent, 0); 202 boolean isIntentSafe = activities.size() > 0; 203 204 // Start an activity if it's safe 205 if (isIntentSafe) { 206 startActivity(mapIntent); 207 } 208 </pre> 209 210 211 212 <h2 id="AppChooser">Show an App Chooser</h2> 213 214 <div class="figure" style="width:200px"> 215 <img src="{@docRoot}images/training/basics/intent-chooser.png" alt="" /> 216 <p class="img-caption"><strong>Figure 2.</strong> Example of the chooser dialog that appears 217 when you use {@link android.content.Intent#createChooser createChooser()} to ensure 218 that the user is always shown a list of apps that respond to your intent.</p> 219 </div> 220 221 <p>Notice that when you start an activity by passing your {@link android.content.Intent} to {@link 222 android.app.Activity#startActivity startActivity()} and there is more than one app that responds to 223 the intent, the user can select which app to use by default (by selecting a checkbox at the bottom 224 of the dialog; see figure 1). This is nice when performing an action for which the user 225 generally wants to use the same app every time, such as when opening a web page (users 226 likely use just one web browser) or taking a photo (users likely prefer one camera). However, if 227 the action to be performed could be handled by multiple apps and the user might 228 prefer a different app each time—such as a "share" action, for which users might have several 229 apps through which they might share an item—you should explicitly show a chooser dialog, 230 which forces the user to select which app to use for the action every time (the user cannot select a 231 default app for the action).</p> 232 233 <p>To show the chooser, create an {@link android.content.Intent} using {@link 234 android.content.Intent#createChooser createChooser()} and pass it to {@link 235 android.app.Activity#startActivity startActivity()}. For example:</p> 236 237 <pre> 238 Intent intent = new Intent(Intent.ACTION_SEND); 239 ... 240 241 // Always use string resources for UI text. This says something like "Share this photo with" 242 String title = getResources().getText(R.string.chooser_title); 243 // Create and start the chooser 244 Intent chooser = Intent.createChooser(intent, title); 245 startActivity(chooser); 246 </pre> 247 248 <p>This displays a dialog with a list of apps that respond to the intent passed to the {@link 249 android.content.Intent#createChooser createChooser()} method and uses the supplied text as the 250 dialog title.</p> 251 252 253 254
