1 page.title=Common Tasks and How to Do Them in Android 2 excludeFromSuggestions=true 3 @jd:body 4 5 <ul> 6 <li><a href="#neweclipseandroidproject">Creating an Android Application using 7 the Eclipse plugin</a></li> 8 <li><a href="#newandroidprojectnoeclipse">Creating an Android Application without 9 the Eclipse plugin</a></li> 10 <li><a href="#addexternallibrary">Adding an External Library (.jar) using Eclipse</a></li> 11 <li><a href="#implementcallbacks">Implementing Activity callbacks</a> (Android 12 calls your activity at various key moments in its life cycle. You must know 13 how to handle each of these to draw your screen, initialize class members, 14 and acquire data.)</li> 15 <li><a href="#opennewscreen">Opening a new screen</a></li> 16 <li><a href="#listening">Listening for button clicks </a></li> 17 <li><a href="#configurewindowproperties">Configuring general window properties </a></li> 18 <li><a href="#localhostalias">Referring to localhost from the emulated environment</a></li> 19 <li><a href="#appstate">Storing and retrieving state</a></li> 20 <li><a href="{@docRoot}guide/topics/data/data-storage.html#preferences">Storing and retrieving preferences</a></li> 21 <li><a href="#storingandretrieving">Storing and retrieving larger or more complex 22 persistent data</a> (files and data) </li> 23 <li><a href="#playback">Playing audio, video, still, or other media files</a></li> 24 <li><a href="#broadcastreceivers">Listening for and broadcasting global messages 25 and setting alarms</a></li> 26 <li><a href="#alerts">Displaying alerts </a></li> 27 <li><a href="#progressbar">Displaying a progress bar</a> </li> 28 <li><a href="#addmenuitems">Adding items to the screen menu</a> </li> 29 <li><a href="#webpage">Display a web page</a> </li> 30 <li><a href="#binding">Binding to data</a></li> 31 <li><a href="#handle">Getting a Handle to a Screen Element</a></li> 32 <li><a href="#captureimages">Capture images from the phone camera </a></li> 33 <li><a href="#threading">Handling expensive operations in the UI thread</a></li> 34 <li><a href="#selectingtext">Selecting, highlighting, or styling portions of 35 text</a></li> 36 <li><a href="#querymap">Utilizing attributes in a Map query</a></li> 37 <li><a href="#filelist">List of files for an Android application</a></li> 38 <li><a href="#logging">Print messages to a log file</a></li> 39 </ul> 40 <p>The ApiDemos sample application includes many, many examples of common 41 tasks and UI features. See the code inside 42 <code><sdk>samples/ApiDemos</code> and the other sample applications 43 under the <code>samples/</code> folder in the SDK.</p> 44 45 46 <h2 id="neweclipseandroidproject">Creating an Android Application using the Eclipse Plugin</h2> 47 48 <p>Using the Android Eclipse plugin is the fastest and easiest way 49 to start creating a new Android application. The plugin automatically generates 50 the correct project structure for your application, and keeps the resources 51 compiled for you automatically.</p> 52 53 <p>It is still a good idea to know what is going on though. Take a look at <a 54 href="{@docRoot}guide/topics/fundamentals.html">Application Fundamentals</a> 55 to understand the basics of how an Android application works.</p> 56 57 <p>You should also take a look at the ApiDemos application and the other sample 58 applications included in the SDK, in the <code><sdk>/samples/</code> 59 folder in the SDK.</p> 60 61 <p>Finally, a great way to started with Android development in Eclipse is to 62 follow both the <a href="{@docRoot}resources/tutorials/hello-world.html">Hello, 63 World</a> and <a 64 href="{@docRoot}training/notepad/index.html">Notepad</a> code 65 tutorials. In particular, the start of the Hello Android tutorial is an 66 excellent introduction to creating a new Android application in Eclipse.</p> 67 68 <h2 id="newandroidprojectnoeclipse">Creating an Android Application without the Eclipse Plugin</h2> 69 70 <p>This topic describes the manual steps in creating an Android application. 71 Before reading this, you should read <a 72 href="{@docRoot}guide/topics/fundamentals.html">Application Fundamentals</a> 73 to understand the basics of how an Android application works. You might also 74 want to look at the sample code included with the Android SDK, in the 75 <code><sdk>/samples/</code> directory. </p> 76 77 <p>Here is a list of the basic steps in building an application.</p> 78 <ol> 79 <li><strong>Create your required resource files</strong> This includes 80 the AndroidManifest.xml global description file, string files that your application 81 needs, and layout files describing your user interface. A full list of optional 82 and required files and syntax details for each is given in <a href="#filelist">File 83 List for an Android Application</a>. </li> 84 <li><strong>Design your user interface</strong> See <a 85 href="{@docRoot}guide/topics/ui/index.html">User Interface</a> for 86 details on elements of the Android screen. </li> 87 <li><strong>Implement your Activity </strong>(this page)<strong> </strong> You 88 will create one class/file for each screen in your application. Screens will 89 inherit from an {@link android.app android.app} class, typically {@link android.app.Activity 90 android.app.Activity} for basic screens, {@link android.app.ListActivity 91 android.app.ListActivity} for list screens, or {@link android.app.Dialog 92 android.app.Dialog} for dialog boxes. You will implement the required callbacks 93 that let you draw your screen, query data, and commit changes, and also perform 94 any required tasks such as opening additional screens or reading data from 95 the device. Common tasks, such as opening a new screen or reading data from 96 the device, are described below. 97 The list of files you'll need for your application are described in <a href="#filelist">List 98 of Files for an Android Application</a>. </li> 99 <li><strong><a href="{@docRoot}guide/developing/building/building-cmdline.html">Build and install your 100 package</a>.</strong> The Android SDK has some nice tools for generating 101 projects and debugging code. </li> 102 </ol> 103 104 <h2 id="addexternallibrary">Adding an External Library (.jar) using Eclipse</h2> 105 <p> 106 You can use a third party JAR in your application by adding it to your Eclipse project as follows: 107 </p> 108 <ol> 109 <li> 110 In the <strong>Package Explorer</strong> panel, right-click on your project and select <strong>Properties</strong>. 111 <li> 112 Select <strong>Java Build Path</strong>, then the tab <strong>Libraries</strong>. 113 <li> 114 Press the <strong>Add External JARs...</strong> button and select the JAR file. 115 </ol> 116 <p> 117 Alternatively, if you want to include third party JARs with your package, create a new directory for them within your project and select <strong>Add Library...</strong> instead.</p> 118 <p> 119 It is not necessary to put external JARs in the assets folder. 120 </p> 121 122 <a name="implementcallbacks" id="implementcallbacks"></a> 123 <h2>Implementing Activity Callbacks</h2> 124 <p>Android calls a number of callbacks to let you draw your screen, store data before 125 pausing, and refresh data after closing. You must implement at least some of 126 these methods. Read the <a 127 href="{@docRoot}guide/topics/fundamentals/activities.html#Lifecycle">Activities</a> 128 document to learn when and in what order these methods 129 are called. Here are some of the standard types of screen classes that Android provides:</p> 130 <ul> 131 <li>{@link android.app.Activity android.app.Activity} - This is a standard screen, 132 with no specialization.</li> 133 <li>{@link android.app.ListActivity android.app.ListActivity} - This is a screen 134 that is used to display a list of something. It hosts a ListView object, 135 and exposes methods to let you identify the selected item, receive callbacks 136 when the selected item changes, and perform other list-related actions. </li> 137 <li>{@link android.app.Dialog android.app.Dialog} - This is a small, popup dialog-style 138 window that isn't intended to remain in the history stack. (It is not resizeable 139 or moveable by the user.)</li> 140 </ul> 141 142 <a name="opennewscreen" id="opennewscreen"></a><h2>Opening a New Screen</h2> 143 <p>Your Activity will often need to open another Activity screen as it progresses. 144 This new screen can be part of the same application or part of another application, 145 the new screen can be floating or full screen, it can return a result, and you 146 can decide whether to close this screen and remove it from the history stack 147 when you are done with it, or to keep the screen open in history. These next 148 sections describe all these options. </p> 149 <h3>Floating or full?<a name="floatingorfull" id="floatingorfull"></a></h3> 150 <p>When you open a new screen you can decide whether to make it transparent or floating, 151 or full-screen. The choice of new screen affects the event sequence of events 152 in the old screen (if the new screen obscures the old screen, a different 153 series of events is called in the old screen). See the <a 154 href="{@docRoot}guide/topics/fundamentals/activities.html#Lifecycle">Activities</a> document for 155 details. </p> 156 <p>Transparent or floating windows are implemented in three 157 standard ways: </p> 158 <ul> 159 <li>Create an {@link android.app.Dialog app.Dialog} class </li> 160 <li>Create an {@link android.app.AlertDialog app.AlertDialog} class </li> 161 <li>Set the {@link android.R.style#Theme_Dialog} <em>theme</em> attribute to <code>@android:style/Theme.Dialog</code> 162 in your AndroidManifest.xml file. For example: 163 <pre><activity class="AddRssItem" android:label="Add an item" android:theme="@android:style/Theme.Dialog"/></pre></li> 164 </ul> 165 166 <p>Calling startActivity() or startActivityForResult() will open a new screen in whatever 167 way it defines itself (if it uses a floating theme it will be floating, 168 otherwise it will be full screen). </p> 169 <h3>Opening a Screen </h3> 170 <p>When you want to open a new screen, you can either explicitly specify the activity 171 class to open, or you can let the operating system decide which screen to open, 172 based upon the data and various parameters you pass in. A screen is opened by 173 calling {@link android.app.Activity#startActivity(android.content.Intent) startActivity} 174 and passing in an {@link android.content.Intent Intent} object, which specifies 175 the criteria for the handling screen. To specify a specific screen, call Intent.setClass 176 or setClassName with the exact activity class to open. Otherwise, set a variety 177 of values and data, and let Android decide which screen is appropriate to open. 178 Android will find one or zero Activities that match the specified requirements; 179 it will never open multiple activities for a single request. More information 180 on Intents and how Android resolves them to a specific class is given in the 181 {@link android.content.Intent Intent} topic. </p> 182 <a name="intentexamples" id="intentexamples"></a><h3>Some Intent examples </h3> 183 <p>The following snippet loads the com.android.samples.Animation1 class, and 184 passes it some arbitrary data.:</p> 185 <pre>Intent myIntent = new Intent(); 186 myIntent.setClassName("com.android.samples", "com.android.samples.Animation1"); 187 myIntent.putExtra("com.android.samples.SpecialValue", "Hello, Joe!"); // key/value pair, where key needs current package prefix. 188 startActivity(myIntent); </pre> 189 <p>The next snippet requests that a Web page be opened by specifying the VIEW action, 190 and a URI data string starting with "http://"; schema:</p> 191 <pre>Intent myIntent = new Intent(Intent.VIEW_ACTION, Uri.parse("http://www.google.com";));</pre> 192 <p>Here is the intent filter from the AndroidManifest.xml file for com.android.browser:</p> 193 <pre><intent-filter> 194 <action android:name="android.intent.action.VIEW" /> 195 <category android:name="android.intent.category.DEFAULT" /> 196 <scheme android:name="http" /> 197 <scheme android:name="https" /> 198 <scheme android:name="file" /> 199 </intent-filter> </pre> 200 <p>Android defines a number of standard values, for instance the action constants 201 defined by {@link android.content.Intent}. You can define custom values, but 202 both the caller and handler must use them. See the <intent-filter> 203 tag description in <a href="{@docRoot}guide/topics/manifest/manifest-intro.html">The AndroidManifest.xml 204 File</a> for more information on the manifest syntax for the handling 205 application. </p> 206 <a name="returningaresult" id="returningaresult"></a><h3>Returning a Result from a Screen</h3> 207 <p>A window can return a result after it closes. This result will be passed back 208 into the calling Activity's {@link android.app.Activity#onActivityResult(int,int,android.content.Intent) 209 onActivityResult()} method, which can supply an Intent containing arbitrary data, along with 210 the request code passed to startActivityForResult(). Note that you must call the {@link 211 android.app.Activity#startActivityForResult(android.content.Intent,int) startActivityForResult()} 212 method that accepts a request code parameter to get this callback. The following 213 code demonstrates opening a new screen and retrieving a result. </p> 214 <pre>// Open the new screen. 215 public void onClick(View v){ 216 // Start the activity whose result we want to retrieve. The 217 // result will come back with request code GET_CODE. 218 Intent intent = new Intent(this, com.example.app.ChooseYourBoxer.class); 219 startActivityForResult(intent, CHOOSE_FIGHTER); 220 } 221 222 // Listen for results. 223 protected void onActivityResult(int requestCode, int resultCode, Intent data){ 224 // See which child activity is calling us back. 225 switch (requestCode) { 226 case CHOOSE_FIGHTER: 227 // This is the standard resultCode that is sent back if the 228 // activity crashed or didn't doesn't supply an explicit result. 229 if (resultCode == RESULT_CANCELED){ 230 myMessageboxFunction("Fight cancelled"); 231 } 232 else { 233 myFightFunction(data); 234 } 235 default: 236 break; 237 } 238 } 239 240 // Class SentResult 241 // Temporary screen to let the user choose something. 242 private OnClickListener mLincolnListener = new OnClickListener(){ 243 public void onClick(View v) { 244 Bundle stats = new Bundle(); 245 stats.putString("height","6\'4\""); 246 stats.putString("weight", "190 lbs"); 247 stats.putString("reach", "74\""); 248 setResult(RESULT_OK, "Lincoln", stats); 249 finish(); 250 } 251 }; 252 253 private OnClickListener mWashingtonListener = new OnClickListener() { 254 public void onClick(View v){ 255 Bundle stats = new Bundle(); 256 stats.putString("height","6\'2\""); 257 stats.putString("weight", "190 lbs"); 258 stats.putString("reach", "73\""); 259 setResult(RESULT_OK, "Washington", stats); 260 finish(); 261 } 262 }; 263 </pre> 264 <h3>Lifetime of the new screen </h3> 265 <p>An activity can remove itself from the history stack by calling {@link android.app.Activity#finish() 266 Activity.finish()} on itself, or the activity that opened the screen can call 267 {@link android.app.Activity#finishActivity(int) Activity.finishActivity()} 268 on any screens that it opens to close them. </p> 269 <a name="listening" id="listening"></a><h2>Listening for Button Clicks</h2> 270 <p>Button click and other UI event capturing are covered in <a 271 href="{@docRoot}guide/topics/ui/ui-events.html">Input Events</a>.</p> 272 <a name="configurewindowproperties" id="configurewindowproperties"></a><h2>Configuring General Window Properties</h2> 273 <p>You can set a number of general window properties, such as whether to display 274 a title, whether the window is floating, and whether it displays an icon, by 275 calling methods on the {@link android.view.Window Window} member 276 of the underlying View object for the window. Examples include calling {@link 277 android.app.Activity#getWindow() getWindow().requestFeature()} (or the convenience 278 method {@link android.app.Activity#requestWindowFeature(int) requestWindowFeature(<em>some_feature</em>)}) 279 to hide the title. Here is an example of hiding the title bar:</p> 280 <pre>//Hide the title bar 281 requestWindowFeature(Window.FEATURE_NO_TITLE); 282 </pre> 283 <p>A better way to achieve the same end is to specify a theme in your Android 284 Manifest file:</p> 285 <pre><application android:icon="@drawable/icon" android:theme="@android:style/Theme.NoTitleBar"> 286 </pre> 287 <p>This is preferable because it tells the system not to show a title bar while 288 your application is starting up. With the explicit method call, your application 289 will have a title bar visible to the user until <code>onCreate</code> runs.</p> 290 <p>(Note that this can be applied to either the <code><application></code> 291 tag or to individual <code><activity></code> tags.)</p> 292 <p class="caution"><strong>Caution:</strong> This theme will also hide the Action Bar on Android 293 3.0 and higher. If you want to keep the Action Bar, but hide the title bar, see how you can <a 294 href="{@docRoot}guide/topics/ui/themes.html#SelectATheme">select a theme based on platform 295 version</a>.</p> 296 <a name="localhostalias" id="localhostalias"></a><h2>Referring to localhost from the emulated 297 environment</h2> 298 <p> 299 If you need to refer to your host computer's <em>localhost</em>, such as when you 300 want the emulator client to contact a server running on the same host, use the alias 301 <code>10.0.2.2</code> to refer to the host computer's loopback interface. 302 From the emulator's perspective, localhost (<code>127.0.0.1</code>) refers to its own 303 loopback interface. 304 </p> 305 <a name="appstate" id="appstate"></a><h2>Storing and Retrieving State</h2> 306 <p>If your application is dumped from memory because of space concerns, it will lose 307 all user interface state information such as checkbox state and text box values 308 as well as class member values. Android calls {@link android.app.Activity#onSaveInstanceState(android.os.Bundle) 309 Activity.onSaveInstanceState} before it pauses the application. This method hands in a {@link 310 android.os.Bundle Bundle} that can be used to store name/value pairs that will 311 persist and be handed back to the application even if it is dropped from memory. 312 Android will pass this Bundle back to you when it calls {@link android.app.Activity#onCreate(android.os.Bundle) 313 onCreate()}. This Bundle only exists while the application is still in the history 314 stack (whether or not it has been removed from memory) and will be lost when 315 the application is finalized. See the topics for {@link android.app.Activity#onSaveInstanceState} and 316 {@link android.app.Activity#onCreate} for 317 examples of storing and retrieving state.</p> 318 <p>Read more about the lifecycle of an activity in <a 319 href="{@docRoot}guide/topics/fundamentals/activities.html">Activities</a> document.</p> 320 <h3>Storing and Retrieving Larger or More Complex Persistent Data<a name="storingandretrieving" id="storingandretrieving"></a></h3> 321 <p>Your application can store files or complex collection objects, and reserve them 322 for private use by itself or other activities in the application, or it can expose 323 its data to all other applications on the device. See <a href="{@docRoot}guide/topics/data/data-storage.html">Storing, 324 Retrieving, and Exposing Data</a> to learn how to store and retrieve private data, 325 how to store and retrieve common data from the device, and how to expose your 326 private data to other applications.</p> 327 <a name="playback" id="playback"></a><h2>Playing Media Files</h2> 328 <p>Please see the document <a href="{@docRoot}guide/topics/media/index.html">Audio and Video</a> for more details.</p> 329 <a name="broadcastreceivers" id="broadcastreceivers"></a><h2>Listening For and Broadcasting Global Messages, and Setting Alarms</h2> 330 <p>You can create a listening class that can be notified or even instantiated whenever 331 a specific type of system message is sent. 332 </p> 333 <p>The listening classes, called broadcast receivers, extend {@link android.content.BroadcastReceiver 334 BroadcastReceiver}. If you want Android to instantiate the object whenever an appropriate 335 intent notification is sent, define the receiver with a <code><receiver></code> element 336 in the AndroidManifext.xml file. If the caller is expected to instantiate the 337 object in preparation to receive a message, this is not required. The receiver 338 will get a call to their {@link android.content.BroadcastReceiver#onReceive(android.content.Context,android.content.Intent) 339 BroadcastReceiver.onReceive()} method. A receiver can define an <code><intent-filter></code> tag 340 that describes the types of messages it will receive. Just as Android's IntentResolver 341 will look for appropriate Activity matches for a startActivity() call, it will 342 look for any matching Receivers (but it will send the message to all matching 343 receivers, not to the "best" match). </p> 344 <p>To send a notification, the caller creates an {@link android.content.Intent Intent} 345 object and calls {@link android.app.Activity#sendBroadcast(android.content.Intent) 346 Context.sendBroadcast()} with that Intent. Multiple recipients can receive 347 the same message. You can broadcast an Intent message to an intent receiver in 348 any application, not only your own. If the receiving class is not registered 349 using <code><receiver></code> in its manifest, you can dynamically instantiate 350 and register a receiver by calling {@link android.content.Context#registerReceiver(android.content.BroadcastReceiver,android.content.IntentFilter) 351 Context.registerReceiver()}. </p> 352 <p>Receivers can include intent filters to specify what kinds of intents they are 353 listening for. Alternatively, if you expect a single known caller to contact 354 a single known receiver, the receiver does not specify an intent filter, and 355 the caller specifies the receiver's class name in the Intent by calling {@link 356 android.content.Intent#setClassName(java.lang.String, java.lang.String) Intent.setClassName()} 357 with the recipient's class name. The recipient receives a {@link android.content.Context 358 Context} object that refers to its own package, not to the package of the sender.</p> 359 <p><em><strong>Note:</strong></em> If a receiver or broadcaster 360 enforces permissions, your application might need to request permission 361 to send or receive messages from that object. You can request permission by using 362 the <uses-permission> tag in the manifest. </p> 363 <p>Here is a code snippet of a sender and receiver. This example does not demonstrate 364 registering receivers dynamically. For a full code example, see the AlarmService 365 class in the ApiDemos project.</p> 366 <h3>Sending the message</h3> 367 <pre>// We are sending this to a specific recipient, so we will 368 // only specify the recipient class name. 369 Intent intent = new Intent(this, AlarmReceiver.class); 370 intent.putExtra("message","Wake up."); 371 sendBroadcast(intent); 372 </pre> 373 <h3>Receiving the message</h3> 374 <p><strong>Receiver AndroidManifest.xml </strong>(because there is no intent filter 375 child, this class will only receive a broadcast when the receiver class is specified 376 by name, as is done in this example):</p> 377 <pre> 378 <receiver class=".AlarmReceiver" /></pre> 379 <p><strong>Receiver Java code: </strong></p> 380 <pre> 381 public class AlarmReceiver extends BroadcastReceiver{ 382 // Display an alert that we've received a message. 383 @Override 384 public void onReceive(Context context, Intent intent){ 385 // Send a text notification to the screen. 386 NotificationManager nm = (NotificationManager) 387 context.getSystemService(Context.NOTIFICATION_SERVICE); 388 nm.notifyWithText(R.id.alarm, 389 "Alarm!!!", 390 NotificationManager.LENGTH_SHORT, 391 null); 392 } 393 } </pre> 394 <h3>Other system messages</h3> 395 <p>You can listen for other system messages sent by Android as well, such as USB 396 connection/removal messages, SMS arrival messages, and timezone changes. See 397 {@link android.content.Intent} for a list of broadcast messages to listen for. 398 Messages are marked "Broadcast Action" in the documentation. </p> 399 <h3>Listening for phone events<a name="phoneevents" id="phoneevents"></a></h3> 400 <p>The {@link android.telephony android.telephony} package overview page describes how to 401 register to listen for phone events. </p> 402 <a name="alarms" id="alarms"></a><h3>Setting Alarms </h3> 403 <p>Android provides an {@link android.app.AlarmManager AlarmManager} service that 404 will let you specify an Intent to send at a designated time. This intent is typically 405 used to start an application at a preset time. (Note: If you want to send 406 a notification to a sleeping or running application, use {@link android.os.Handler 407 Handler} instead.)</p> 408 <a name="alerts" id="alerts"></a><h2>Displaying Alerts</h2> 409 <p>There are two major kinds of alerts that you may display to the user: 410 (1) Normal alerts are displayed in response to a user action, such as 411 trying to perform an action that is not allowed. (2) Out-of-band alerts, 412 called notifications, are 413 displayed as a result of something happening in the background, such as the 414 user receiving new e-mail.</p> 415 416 <a name="dialogsandalerts" id="dialogsandalerts"></a><h3>Normal Alerts</h3> 417 418 <p>Android provides a number of ways for you to show popup notifications to your 419 user as they interact with your application. </p> 420 <table width="100%" border="1"> 421 <tr> 422 <th scope="col">Class</th> 423 <th scope="col">Description</th> 424 </tr> 425 <tr> 426 <td>{@link android.app.Dialog app.Dialog}</td> 427 <td>A generic floating dialog box with a layout that you design. </td> 428 </tr> 429 <tr> 430 <td><p>{@link android.app.AlertDialog app.AlertDialog}</p></td> 431 <td>A popup alert dialog with two buttons (typically OK and Cancel) that 432 take callback handlers. See the section after this table for more details. </td> 433 </tr> 434 <tr> 435 <td>{@link android.app.ProgressDialog ProgressDialog} </td> 436 <td>A dialog box used to indicate progress of an operation with a known progress 437 value or an indeterminate length (setProgress(bool)). See <strong>Views</strong> > <strong>Progress Bar</strong> in 438 ApiDemos for examples. </td> 439 </tr> 440 <tr> 441 <td>Activity</td> 442 <td>By setting the theme of an activity to 443 {@link android.R.style#Theme_Dialog 444 android:theme="@android:style/Theme.Dialog"}, 445 your activity will take on 446 the appearance of a normal dialog, floating on top of whatever was 447 underneath it. You usually set the theme through the 448 {@link android.R.attr#theme android:theme} attribute in your AndroidManifest.xml. 449 The advantage of this 450 over Dialog and AlertDialog is that Application has a much better managed 451 life cycle than dialogs: if a dialog goes to the background and is killed, 452 you cannot recapture state, whereas Application exposes a {@link android.os.Bundle 453 Bundle} of saved values in <code>onCreate()</code> to help you maintain state.</td> 454 </tr> 455 </table> 456 <h3>AlertDialog</h3> 457 <p>This is a basic warning dialog box that lets you configure a message, button text, 458 and callback. You can create one by calling using the {@link 459 android.app.AlertDialog.Builder} class, as shown here. </p> 460 <pre>private Handler mHandler = new Handler() { 461 public void handleMessage(Message msg) { 462 switch (msg.what) { 463 case ACCEPT_CALL: 464 answer(msg.obj); 465 break; 466 467 case BOUNCE_TO_VOICEMAIL: 468 voicemail(msg.obj); 469 break; 470 471 } 472 } 473 }; 474 475 476 private void IncomingMotherInlawCall(Connection c) { 477 String Text; 478 479 // "Answer" callback. 480 Message acceptMsg = Message.obtain(); 481 acceptMsg.target = mHandler; 482 acceptMsg.what = ACCEPT_CALL; 483 acceptMsg.obj = c.getCall(); 484 485 // "Cancel" callback. 486 final Message rejectMsg = Message.obtain(); 487 rejectMsg.target = mHandler; 488 rejectMsg.what = BOUNCE_TO_VOICEMAIL; 489 rejectMsg.obj = c.getCall(); 490 491 new AlertDialog.Builder(this) 492 .setMessage("Phyllis is calling") 493 .setPositiveButton("Answer", acceptMsg) 494 .setOnCanceListener(new OnCancelListener() { 495 public void onCancel(DialogInterface dialog) { 496 rejectMsg.sendToTarget(); 497 }}); 498 .show(); 499 } </pre> 500 501 <h3>Notifications</h3> 502 503 <p>Out-of-band alerts should always be displayed using the 504 {@link android.app.NotificationManager}, which allows you to tell the user 505 about something they may be interested in without disrupting what they are 506 currently doing. A notification can be anything from a brief pop-up box 507 informing the user of the new information, through displaying a persistent 508 icon in the status bar, to vibrating, playing sounds, or flashing lights to 509 get the user's attention. In all cases, the user must explicitly shift their 510 focus to the notification before they can interact with it.</p> 511 512 <p>The following code demonstrates using NotificationManager to display a basic text 513 popup when a new SMS message arrives in a listening service, and provides the 514 current message count. You can see several more examples in the ApiDemos application, 515 under app/ (named <em>notification</em>*.java).</p> 516 <pre>static void setNewMessageIndicator(Context context, int messageCount){ 517 // Get the static global NotificationManager object. 518 NotificationManager nm = NotificationManager.getDefault();</p> 519 520 // If we're being called because a new message has been received, 521 // then display an icon and a count. Otherwise, delete the persistent 522 // message. 523 if (messageCount > 0) { 524 nm.notifyWithText(myApp.NOTIFICATION_GUID, // ID for this notification. 525 messageCount + " new message" + messageCount > 1 ? "s":"", // Text to display. 526 NotificationManager.LENGTH_SHORT); // Show it for a short time only. 527 } 528 }</pre> 529 <p>To display a notification in the status bar and have it launch an intent when 530 the user selects it (such as the new text message notification does), call {@link 531 android.app.NotificationManager#notify(int, android.app.Notification) NotificationManager.notify()}, 532 and pass in vibration patterns, status bar icons, or Intents to associate with 533 the notification. </p> 534 <a name="progressbar" id="progressbar"></a><h2>Displaying a Progress Bar</h2> 535 <p>An activity can display a progress bar to notify the user that something is happening. 536 To display a progress bar in a screen, call {@link android.app.Activity#requestWindowFeature(int) 537 Activity.requestWindowFeature(Window.FEATURE_PROGRESS)}. To set the value 538 of the progress bar, call {@link android.view.Window#setFeatureInt(int,int) 539 Activity.getWindow().setFeatureInt(Window.FEATURE_PROGRESS, <em>level</em>)}. 540 Progress bar values are from 0 to 9,999, or set the value to 10,000 to make the 541 progress bar invisible. </p> 542 <p>You can also use the {@link android.app.ProgressDialog ProgressDialog} class, 543 which enables a dialog box with an embedded progress bar to send a "I'm working 544 on it" notification to the user. </p> 545 <a name="addmenuitems" id="addmenuitems"></a><h2>Adding Items to the Screen Menu</h2> 546 <p>See <a href="{@docRoot}guide/topics/ui/menus.html">Menus</a>.</p> 547 548 <a name="webpage" id="webpage"></a><h2>Display a Web Page</h2> 549 <p>Use the {@link android.webkit.WebView webkit.WebView} object. </p> 550 <a name="binding" id="binding"></a><h2>Binding to Data</h2> 551 <p>You can bind a ListView to a set of underlying data by using a shim class called 552 {@link android.widget.ListAdapter ListAdapter} (or a subclass). ListAdapter subclasses 553 bind to a variety of data sources, and expose a common set of methods such as 554 getItem() and getView(), and uses them to pick View items to display in its list. 555 You can extend ListAdapter and override getView() to create your own custom list 556 items. There are essentially only two steps you need to perform to bind to data: </p> 557 <ol> 558 <li>Create a ListAdapter object and specify its data source</li> 559 <li>Give the ListAdapter to your ListView object.</li> 560 </ol> 561 <p>That's it!</p> 562 <p>Here's an example of binding a ListActivity screen to the results from a cursor 563 query. (Note that the setListAdapter() method shown is a convenience method that 564 gets the page's ListView object and calls setAdapter() on it.)</p> 565 <pre>// Run a query and get a Cursor pointing to the results. 566 Cursor c = People.query(this.getContentResolver(), null); 567 startManagingCursor(c); 568 569 // Create the ListAdapter. A SimpleCursorAdapter lets you specify two interesting things: 570 // an XML template for your list item, and 571 // The column to map to a specific item, by ID, in your template. 572 ListAdapter adapter = new SimpleCursorAdapter(this, 573 android.R.layout.simple_list_item_1, // Use a template that displays a text view 574 c, // Give the cursor to the list adapter 575 new String[] {People.NAME} , // Map the NAME column in the people database to... 576 new String[] {"text1"}); // The "text1" view defined in the XML template 577 setListAdapter(adapter);</pre> 578 <p>See view/List4 in the ApiDemos project for an example of extending ListAdapter 579 for a new data type. </p> 580 581 <a name="handle"></a> 582 583 <h2>Getting a Handle to a Screen Element</h2> 584 <p>You can get a handle to a screen element by calling {@link 585 android.app.Activity#findViewById(int) Activity.findViewById}. You can then use 586 the handle to set or retrieve any values exposed by the object. </p> 587 <a name="captureimages" id="captureimages"></a><h2>Capture Images from the Phone Camera</h2> 588 <p>You can hook into the device's camera onto your own Canvas object by using the 589 {@link android.hardware.Camera Camera} class. See that class's documentation, 590 and the ApiDemos project's Camera Preview application (Graphics/Camera Preview) 591 for example code. </p> 592 593 594 <a name="threading" id="threading"></a><h2>Handling Expensive Operations in the UI Thread</h2> 595 <p>Avoid performing long-running operations (such as network I/O) directly in the UI thread — 596 the main thread of an application where the UI is run — or your application may be blocked 597 and become unresponsive. Here is a brief summary of the recommended approach for handling expensive operations:</p> 598 <ol> 599 <li>Create a Handler object in your UI thread</li> 600 <li>Spawn off worker threads to perform any required expensive operations</li> 601 <li>Post results from a worker thread back to the UI thread's handler either through a Runnable or a {@link android.os.Message}</li> 602 <li>Update the views on the UI thread as needed</li> 603 </ol> 604 605 <p>The following outline illustrates a typical implementation:</p> 606 607 <pre> 608 public class MyActivity extends Activity { 609 610 [ . . . ] 611 // Need handler for callbacks to the UI thread 612 final Handler mHandler = new Handler(); 613 614 // Create runnable for posting 615 final Runnable mUpdateResults = new Runnable() { 616 public void run() { 617 updateResultsInUi(); 618 } 619 }; 620 621 @Override 622 protected void onCreate(Bundle savedInstanceState) { 623 super.onCreate(savedInstanceState); 624 625 [ . . . ] 626 } 627 628 protected void startLongRunningOperation() { 629 630 // Fire off a thread to do some work that we shouldn't do directly in the UI thread 631 Thread t = new Thread() { 632 public void run() { 633 mResults = doSomethingExpensive(); 634 mHandler.post(mUpdateResults); 635 } 636 }; 637 t.start(); 638 } 639 640 private void updateResultsInUi() { 641 642 // Back in the UI thread -- update our UI elements based on the data in mResults 643 [ . . . ] 644 } 645 } 646 </pre> 647 648 <p>For further discussions on this topic, see 649 <a href="{@docRoot}guide/practices/design/responsiveness.html">Designing for Responsiveness</a> 650 and the {@link android.os.Handler} documentation.</p> 651 652 <a name="selectingtext" id="selectingtext"></a><h2>Selecting, Highlighting, or Styling Portions of Text</h2> 653 <p>You can highlight or style the formatting of strings or substrings of text in 654 a TextView object. There are two ways to do this:</p> 655 <ul> 656 <li>If you use a <a href="{@docRoot}guide/topics/resources/available-resources.html#stringresources">string resource</a>, 657 you can add some simple styling, such as bold or italic using HTML notation. 658 The currently supported tags are: <code>B</code> (bold), 659 <code>I</code> (italic), <code>U</code> (underline), 660 <code>TT</code> (monospace), <code>BIG</code>, <code>SMALL</code>, 661 <code>SUP</code> (superscript), <code>SUB</code> (subscript), 662 and <code>STRIKE</code> (strikethrough). 663 So, for example, in res/values/strings.xml you could declare this:<br /> 664 <code><resource><br /> 665 <string id="@+id/styled_welcome_message">We 666 are <b><i>so</i></b> glad to see you.</string><br /> 667 </resources></code></li> 668 <li>To style text on the fly, or to add highlighting or more complex styling, 669 you must use the Spannable object as described next. </li> 670 </ul> 671 <p>To style text on the fly, you must make sure the TextView is using {@link android.text.Spannable} 672 storage for the text (this will always be true if the TextView is an EditText), 673 retrieve its text with {@link android.widget.TextView#getText}, and call {@link 674 android.text.Spannable#setSpan}, passing in a new style class from the {@link 675 android.text.style} package and the selection range. </p> 676 <p>The following code snippet demonstrates creating a string with a highlighted section, 677 italic section, and bold section, and adding it to an EditText object. </p> 678 <pre>// Get our EditText object. 679 EditText vw = (EditText)findViewById(R.id.text); 680 681 // Set the EditText's text. 682 vw.setText("Italic, highlighted, bold."); 683 684 // If this were just a TextView, we could do: 685 // vw.setText("Italic, highlighted, bold.", TextView.BufferType.SPANNABLE); 686 // to force it to use Spannable storage so styles can be attached. 687 // Or we could specify that in the XML. 688 689 // Get the EditText's internal text storage 690 Spannable str = vw.getText(); 691 692 // Create our span sections, and assign a format to each. 693 str.setSpan(new StyleSpan(android.graphics.Typeface.ITALIC), 0, 7, Spannable.SPAN_EXCLUSIVE_EXCLUSIVE); 694 str.setSpan(new BackgroundColorSpan(0xFFFFFF00), 8, 19, Spannable.SPAN_EXCLUSIVE_EXCLUSIVE); 695 str.setSpan(new StyleSpan(android.graphics.Typeface.BOLD), 21, str.length() - 1, Spannable.SPAN_EXCLUSIVE_EXCLUSIVE); 696 </pre> 697 698 <a name="querymap" id="querymap"></a><h2>Utilizing attributes in a Map query</h2> 699 <p> 700 When using a search intent to ask the Maps activity to search for something, the Maps activity responds to the following attributes in the optional context bundle: 701 </p> 702 <pre> 703 float "centerLatitude" default 0.0f 704 float "centerLongitude" default 0.0f 705 float "latitudeSpan" default 0.0f 706 float "longitudeSpan" default 0.0f 707 int "zoomLevel" default 10 708 </pre> 709 <p> 710 This context information is used to center the search result in a particular area, and is equivalent to adjusting the Map activity to the described location and zoom level before issuing the query. 711 </p> 712 <p> 713 If the latitudeSpan, longitudeSpan, and zoomLevel attributes are not consistent, then it is undefined which one takes precedence. 714 </p> 715 716 <a name="filelist" id="filelist"></a><h2>List of Files for an Android Application</h2> 717 <p>The following list describes the structure and files of an Android application. 718 Many of these files can be built for you (or stubbed out) by the android tool 719 shipped in the tools/ menu of the SDK. </p> 720 <table width="100%" border="0"> 721 <tr> 722 <td width="28%" valign="top">MyApp/<br /></td> 723 <td width="72%" valign="top"> </td> 724 </tr> 725 <tr> 726 <td valign="top"> AndroidManifest.xml</td> 727 <td valign="top">(<em>required</em>) Advertises the screens that this application provides, 728 where they can be launched (from the main program menu or elsewhere), 729 any content providers it implements and what kind of data they handle, 730 where the implementation classes are, and other application-wide 731 information. Syntax details for this file are described in <a href="{@docRoot}guide/topics/manifest/manifest-intro.html">The AndroidManifest.xml File</a>.</td> 732 </tr> 733 <tr> 734 <td valign="top"> src/<br /> 735 /<em>myPackagePath</em>/.../<em>MyClass</em>.java</td> 736 <td valign="top">(<em>required</em>) This folder holds all the source code files for your 737 application, inside the appropriate package subfolders. </td> 738 </tr> 739 <tr> 740 <td valign="top"> res/</td> 741 <td valign="top">(<em>required</em>) This folder holds all the <em>resources</em> for 742 your application. Resources are external data files or description files 743 that are compiled into your code at build time. Files in different folders 744 are compiled differently, so you must put the proper resource into the 745 proper folder. (See <a href="{@docRoot}guide/topics/resources/resources-i18n.html">Resources</a> for details.)</td> 746 </tr> 747 <tr> 748 <td valign="top"> anim/<br /> 749 <em>animation1</em>.xml<br /> 750 <em>...</em></td> 751 <td valign="top">(<em>optional</em>) Holds any animation XML description files that the 752 application uses. The format of these files is described in <a href="{@docRoot}guide/topics/resources/resources-i18n.html">Resources</a>. </td> 753 </tr> 754 <tr> 755 <td valign="top"> drawable/<br /> 756 <em>some_picture</em>.png<br /> 757 <em>some_stretchable</em>.9.png<br /> 758 <em>some_background</em>.xml<br /> 759 ...</td> 760 <td valign="top">(<em>optional</em>) Zero or more files that will be compiled to {@link 761 android.graphics.drawable android.graphics.drawable} resources. Files 762 can be image files (png, gif, or other) or XML files describing other 763 graphics such as bitmaps, stretchable bitmaps, or gradients. Supported 764 bitmap file formats are PNG (preferred), JPG, and GIF (discouraged), 765 as well as the custom 9-patch stretchable bitmap format. These formats 766 are described in <a href="{@docRoot}guide/topics/resources/resources-i18n.html">Resources</a>. </td> 767 </tr> 768 <tr> 769 <td valign="top"> layout/<br /> 770 <em>screen_1_layout</em>.xml<br /> 771 ...<br /></td> 772 <td valign="top">(<em>optional</em>) Holds all the XML files describing screens or parts 773 of screens. Although you could create a screen in Java, defining them 774 in XML files is typically easier. A layout file is similar in concept 775 to an HTML file that describes the screen layout and components. See <a href="{@docRoot}guide/topics/ui/index.html">User Interface</a> for more information about designing screens, and <a href="{@docRoot}guide/topics/resources/available-resources.html#layoutresources">Available Resource Types</a> for the syntax of these files.</td> 776 </tr> 777 <tr> 778 <td valign="top"> values/<br /> 779 arrays<br /> 780 classes.xml<br /> 781 colors.xml<br /> 782 dimens.xml<br /> 783 strings.xml<br /> 784 styles.xml<br /> 785 values.xml<br /></td> 786 <td valign="top"><p>(<em>optional</em>) XML files describing additional resources 787 such as strings, colors, and styles. The naming, quantity, and number 788 of these files are not enforced--any XML file is compiled, but these 789 are the standard names given to these files. However, the syntax 790 of these files is prescribed by Android, and described in <a href="{@docRoot}guide/topics/resources/resources-i18n.html">Resources</a>. </p> 791 </td> 792 </tr> 793 <tr> 794 <td valign="top"> xml/</td> 795 <td valign="top">(<em>optional</em>) XML files that can be read at run time on the device. </td> 796 </tr> 797 <tr> 798 <td valign="top"> raw/</td> 799 <td valign="top">(<em>optional</em>) Any files to be copied directly to the device. </td> 800 </tr> 801 </table> 802 803 804 <a name="logging" ></a> 805 <h2>Print Messages to a Log File</h2> 806 807 <p>To write log messages from your application:</p> 808 <ol><li>Import <code>android.util.Log</code>.</li> 809 <li>Use <code>Log.v()</code>, <code>Log.d()</code>, <code>Log.i()</code>, 810 <code>Log.w()</code>, or <code>Log.e()</code> to log messages. 811 (See the {@link android.util.Log} class.)<br/> E.g., 812 <code>Log.e(this.toString(), "error: " + err.toString())</code></li> 813 <li>Launch <a href="{@docRoot}guide/developing/tools/ddms.html">DDMS</a> from a terminal 814 by executing <code>ddms</code> in your Android SDK <code>/tools</code> path.</li> 815 <li>Run your application in the Android emulator.</li> 816 <li>From the DDMS application, select the emulator 817 (e.g., "emulator-5554") and click <b>Device > Run logcat...</b> 818 to view all the log data.</li> 819 </ol> 820 <p class="note"><strong>Note:</strong> If you are running Eclipse and 821 encounter a warning about the VM debug port when opening DDMS, you can ignore it 822 if you're only interested in logs. However, if you want to further inspect and 823 control your processes from DDMS, then you should close Eclipse before launching DDMS so that 824 it may use the VM debugging port.</p> 825 826 827
