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This article describes a technique you can use to find out whether the system contains any application capable of responding to the intent you want to use. The example below shows a helper method that queries the system package manager to determine whether there's an app that can respond to a specified intent. Your application can pass an intent to the method and then, for example, show or hide user options that the user would normally use to trigger the intent.

/** * Indicates whether the specified action can be used as an intent. This * method queries the package manager for installed packages that can * respond to an intent with the specified action. If no suitable package is * found, this method returns false. * * @param context The application's environment. * @param action The Intent action to check for availability. * * @return True if an Intent with the specified action can be sent and *         responded to, false otherwise. */public static boolean isIntentAvailable(Context context, String action) {    final PackageManager packageManager = context.getPackageManager();    final Intent intent = new Intent(action);    List<ResolveInfo> list =            packageManager.queryIntentActivities(intent,                    PackageManager.MATCH_DEFAULT_ONLY);    return list.size() > 0;}

@Overridepublic boolean onPrepareOptionsMenu(Menu menu) {    final boolean scanAvailable = isIntentAvailable(this,        "com.google.zxing.client.android.SCAN");    MenuItem item;    item = menu.findItem(R.id.menu_item_add);    item.setEnabled(scanAvailable);    return super.onPrepareOptionsMenu(menu);}

An AppWidgetProvider is a BroadcastReceiver. That gives you two possibilities right off the bat: 1. Have it also handle whatever other Intents you were planning on setting up with a separate BroadcastReceiver, or 2. Send an Intent from whatever component you want to the AppWidgetProvider. In other words, don't worry about trying to talk directly to the app widget (which I suspect is impossible) -- just talk to your code that already talks to the app widget.

I update my widget from within my app, when I delete/add entries to a list. To do this, I have a method (updateWidget) and a static String (UPDATE_ACTION). My updateWidget() method sends a broadcast which is received by the widget class and then calls onUpdate() with the appropriate params: private void updateWidget() {                 Intent i = new Intent(this, TVWidget.class);                 i.setAction(TVWidget.UPDATE_ACTION);                 sendBroadcast(i);         } In TVWidget class: @Override         public void onReceive(Context context, Intent intent) {                 String action = intent.getAction();                 if (action != null && action.equals(UPDATE_ACTION)) {                         final AppWidgetManager manager = AppWidgetManager.getInstance (context);                         onUpdate(context, manager,                                         manager.getAppWidgetIds(new ComponentName(                                                         context, TVWidget.class)                                         )                         );                 }                 else {                         super.onReceive(context, intent);                 }         } This seems to work fine.

The Android system reuses Intents that match both action and scheme values—the "extras" values are not compared

In practice, this means the Intent for each App Widget identifier would actually be the same Intent. Fortunately, the solution is straightforward: define a scheme for your App Widget and use it to define unique Intent instances

// make this pending intent unique widgetUpdate.setData( Uri.withAppendedPath(Uri.parse( ImagesWidgetProvider.URI_SCHEME + "://widget/id/"), String.valueOf(appWidgetId)));

Intent videoClient = new Intent(Intent.ACTION_VIEW);    videoClient.setData(Uri.parse("http://m.youtube.com/watch?v="+videoId));    videoClient.setClassName("com.google.android.youtube", "com.google.android.youtube.PlayerActivity");    startActivityForResult(videoClient, VIDEO_APP);

I am just making some AppWidget and I want to pass some Strings through UpdateView to an Activity. But the Bundle is null. I try this: -Widget.java                       Intent defineIntent = new Intent(context, Visor.class);                        defineIntent.putExtra ("org.rss.androides.post2","artist");                        PendingIntent pendingIntent = PendingIntent.getActivity(context, 0, defineIntent, 0);                        updateViews.setOnClickPendingIntent (R.id.widget, pendingIntent); -Viewer.java           Bundle b = intent.getExtras();                 if (b == null) {                     finish();                     return;                 } b is always null.

Remember that PendingIntents aren't keyed using extras: http://groups.google.com/group/android-developers/msg/b296f43ae70c4587 You could hack the extras through by mangling them into Uri parameters, or if you're using a ContentProvider, just point to a specific row.

Or use PendingIntent.FLAG_UPDATE_CURRENT; just be careful that each active instance has its own unique Intent.

On an HTC Hero, this EXTRA_OUTPUT doesn't even work. It doesn't put your picture in the file you specify, but it hands it to you thru a Mediastore uri. Apparently, the only way to get a full size picture is to do all camera handling in your app instead of using the IMAGE_CAPTURE intent.

I think Google have missed a trick on this one. They have defined standard intents for media capture, but not specified standard responses (ie. the "data" parameter in the onActivityResult Activity callback method). Other Android vendors (e.g. HTC Hero) have created their own Camera applications that handle the standard IMAGE_CAPTURE intent, but return different data & have different ways to save/return the image information. All I want is to be able to fire a IMAGE_CAPTURE intent from my own app, and get back a Uri reference to the captured image. Simple. I have no requirement to further manipulate the image .. I just need the Uri to store in my app's database for future reference.

I am just getting started with Android development and I have created a nice little widget that displays some info on my home screen. However, I now want to implement a Button on my widget that updates the info in my widget TextView.

Solved - I can confirm that an Activity is NOT needed if you want create a Button to update an Android AppWidget. I have been able to implement my AppWidgetProvider class such that it registers an android.appwidget.action.APPWIDGET_UPDATE intent-filter with the Broadcast receiver in the AndroidManifest.xml, which then fires the onUpdate event in the AppWidgetProvider class (which in turn then runs the UpdateService).

The UpdateService in my AppWidgetProvider class then uses onHandleIntent to run a private buildUpdate method - which registers the onClick event with a call to setOnClickPendingIntent as follows:

Intent picMessageIntent = new Intent(android.content.Intent.ACTION_SEND);  picMessageIntent.setType("image/jpeg");    File downloadedPic =  new File(      Environment.getExternalStoragePublicDirectory(      Environment.DIRECTORY_DOWNLOADS),      "q.jpeg");    picMessageIntent.putExtra(Intent.EXTRA_STREAM, Uri.fromFile(downloadedPic));  

launches the pending intent

checkout flow finishes

Since: API Level 3

Constants for supporting speech recognition through starting an Intent

Then i've tried PendingIntent.FLAG_UPDATE_CURRENT i'm no longer crashing, but it always launches the activity with extras were put in the widget that was updated the last. It looks like pending intent is shared among my widget instances

I've changed the call to  PendingIntent pending = PendingIntent.getActivity(context, appWidgetId, intent, PendingIntent.FLAG_UPDATE_CURRENT); Now everything is cool except based on discussions i'm not sure how reliable it'll be . ( Doc says it's not supported yet )

基于Unix（Linux）的系统都有一个很优秀的传统，就是倡导非常轻便的进程间通信（IPC）机制；倡导进程通过IPC来互相协作；倡导功能单一，小巧而强壮的进程，而不是又大又复杂的“万金油”

Android的组件和进程间通信都建立在一种基于称为Intent的消息基础之上。Intent就是一种消息，它包含了两个重要的内容：1. 消息的目的，即这个消息是发给哪个组件的？（消息的目的中不会包含“消息是发给哪个进程”这样的信息，这里Android有意淡化进程的概念，而只让我们关心组件，因为了解太多关于进程的具体信息会加大复杂度，而又如何做到进程间的消息传递呢？下文会说到一种Android中关于这点比较特别的设计方式，我认为是一种简捷有用又符合手机特点的设计）；2. 消息所携带的数据内容，即需要传递给目标的数据。下面是一个简单的利用Intent来启动一个Service并向其传递数据的代码示例

这种模式的消息由于已经确切知道了消息目标的确切信息，所以只适用于同一进程内的不同组件之间通信，例如打开一个子窗体，和同一进程中的service通信等。对应的，隐式消息就一般用于跨进程的通信了，隐式消息没有确定的消息目的地，除了数据外，隐式消息只是包含了一些用于表征消息特征的描述字段

> Now I just want to update the GUI from this method. > Can I somehow call a method in PushEndpointDemo.java? No, for two reasons: 1. Because C2DMReceiver is a manifest-registered BroadcastReceiver and therefore has no access to any activities 2. There might not be an activity, since you have no control over the timing of when the C2DM message is received (e.g., the user pressed BACK, the user pressed HOME) > Do I need a Broadcast Intent to do this? Possibly. -- If you want to update an activity or else ignore the message, have C2DMReceiver send out a private broadcast, picked up by a receiver registered via registerReceiver() in the activity -- If you want to update an activity or else raise a notification, have C2DMReceiver send out an ordered broadcast, as described here: http://commonsware.com/blog/2010/08/11/activity-notification-ordered-... -- If you want to update a database, call startActivity() on an IntentService, and have it do the database I/O, plus possibly broadcast an Intent to update an activity/raise a notification.

A facility for the application to tell the system about something it wants to be doing in the background

A facility for an application to expose some of its functionality to other applications.