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1、App WidgetsApp Widgets are miniature application views that can be embedded in other applications (such as the Home screen) and receive periodic updates. These views are referred to as Widgets in the user interface, and you can publish one with an App Widget provider. An application component that i
2、s able to hold other App Widgets is called an App Widget host. The screenshot below shows the Music App Widget.This document describes how to publish an App Widget using an App Widget provider.The BasicsTo create an App Widget, you need the following:AppWidgetProviderInfo objectDescribes the metadat
3、a for an App Widget, such as the App Widgets layout, update frequency, and the AppWidgetProvider class. This should be defined in XML.AppWidgetProvider class implementation Defines the basic methods that allow you to programmatically interface with the App Widget, based on broadcast events. Through
4、it, you will receive broadcasts when the App Widget is updated, enabled, disabled and deleted.View layout Defines the initial layout for the App Widget, defined in XML.Additionally, you can implement an App Widget configuration Activity. This is an optional Activity that launches when the user adds
5、your App Widget and allows him or her to modify App Widget settings at create-time.The following sections describe how to setup each of these components.Declaring an App Widget in the ManifestFirst, declare the AppWidgetProvider class in your applications AndroidManifest.xml file. For example : The
6、element requires the android:name attribute, which specifies the AppWidgetProvider used by the App Widget.The element must include an element with the android:name attribute. This attribute specifies that the AppWidgetProvider accepts the ACTION_APPWIDGET_UPDATE broadcast. This is the only broadcast
7、 that you must explicitly declare. The AppWidgetManager automatically sends all other App Widget broadcasts to the AppWidgetProvider as necessary.The element specifies the AppWidgetProviderInfo resource and requires the following attributes: android:name - Specifies the metadata name. Use android.ap
8、pwidget.provider to identify the data as the AppWidgetProviderInfo descriptor. android:resource - Specifies the AppWidgetProviderInfo resource location.Adding the AppWidgetProviderInfo Metadata The AppWidgetProviderInfo defines the essential qualities of an App Widget, such as its minimum layout dim
9、ensions, its initial layout resource, how often to update the App Widget, and (optionally) a configuration Activity to launch at create-time. Define the AppWidgetProviderInfo object in an XML resource using a single element and save it in the projects res/xml/ folder.For example :appwidget-provider
10、xmlns:android= android:minWidth=294dp android:minHeight=72dp android:updatePeriodMillis=86400000 android:initialLayout=layout/example_appwidget android:configure=com.example.android.ExampleAppWidgetConfigure Heres a summary of the attributes: The values for the minWidth and minHeight attributes spec
11、ify the minimum area required by the App Widgets layout.The default Home screen positions App Widgets in its window based on a grid of cells that have a defined height and width. If the values for an App Widgets minimum width or height dont match the dimensions of the cells, then the App Widget dime
12、nsions round up to the nearest cell size. (See the App Widget Design Guidelines for more information on the Home screen cell sizes.)Because the Home screens layout orientation (and thus, the cell sizes) can change, as a rule of thumb, you should assume the worst-case cell size of 74 pixels for the h
13、eight and width of a cell. However, you must subtract 2 from the final dimension to account for any integer rounding errors that occur in the pixel count. To find your minimum width and height in density-independent pixels (dp), use this formula:(number of cells * 74) 2Following this formula, you sh
14、ould use 72 dp for a height of one cell, 294 dp and for a width of four cells. The updatePeriodMillis attribute defines how often the App Widget framework should request an update from the AppWidgetProvider by calling the onUpdate() method. The actual update is not guaranteed to occur exactly on tim
15、e with this value and we suggest updating as infrequently as possibleperhaps no more than once an hour to conserve the battery. You might also allow the user to adjust the frequency in a configurationsome people might want a stock ticker to update every 15 minutes, or maybe only four times a day.Not
16、e: If the device is asleep when it is time for an update (as defined by updatePeriodMillis), then the device will wake up in order to perform the update. If you dont update more than once per hour, this probably wont cause significant problems for the battery life. If, however, you need to update mo
17、re frequently and/or you do not need to update while the device is asleep, then you can instead perform updates based on an alarm that will not wake the device. To do so, set an alarm with an Intent that your AppWidgetProvider receives, using the AlarmManager. Set the alarm type to either ELAPSED_RE
18、ALTIME or RTC, which will only deliver the alarm when the device is awake. Then set updatePeriodMillis to zero (0). The initialLayout attribute points to the layout resource that defines the App Widget layout. The configure attribute defines the Activity to launch when the user adds the App Widget,
19、in order for him or her to configure App Widget properties. This is optional (read Creating an App Widget Configuration Activity below).See the AppWidgetProviderInfo class for more information on the attributes accepted by the element.Creating the App Widget Layout You must define an initial layout
20、for your App Widget in XML and save it in the projects res/layout/ directory. You can design your App Widget using the View objects listed below, but before you begin designing your App Widget, please read and understand the App Widget Design Guidelines.Creating the App Widget layout is simple if yo
21、ure familiar with Declaring Layout in XML. However, you must be aware that App Widget layouts are based on RemoteViews, which do not support every kind of layout or view widget.A RemoteViews object (and, consequently, an App Widget) can support the following layout classes: FrameLayout LinearLayout
22、RelativeLayoutAnd the following widget classes : AnalogClock Button Chronometer ImageButton ImageView ProgressBar TextViewDescendants of these classes are not supported.Using the AppWidgetProvider ClassYou must declare your AppWidgetProvider class implementation as a broadcast receiver using the ele
23、ment in the AndroidManifest (see Declaring an App Widget in the Manifest above).The AppWidgetProvider class extends BroadcastReceiver as a convenience class to handle the App Widget broadcasts. The AppWidgetProvider receives only the event broadcasts that are relevant to the App Widget, such as when
24、 the App Widget is updated, deleted, enabled, and disabled. When these broadcast events occur, the AppWidgetProvider receives the following method calls:onUpdate(Context, AppWidgetManager, int)This is called to update the App Widget at intervals defined by the updatePeriodMillis attribute in the App
25、WidgetProviderInfo (see Adding the AppWidgetProviderInfo Metadata above). This method is also called when the user adds the App Widget, so it should perform the essential setup, such as define event handlers for Views and start a temporary Service, if necessary. However, if you have declared a confi
26、guration Activity, this method is not called when the user adds the App Widget, but is called for the subsequent updates. It is the responsibility of the configuration Activity to perform the first update when configuration is done. (See Creating an App Widget Configuration Activity below.) onDelete
27、d(Context, int) This is called every time an App Widget is deleted from the App Widget host. onEnabled(Context)This is called when an instance the App Widget is created for the first time. For example, if the user adds two instances of your App Widget, this is only called the first time. If you need
28、 to open a new database or perform other setup that only needs to occur once for all App Widget instances, then this is a good place to do it. onDisabled(Context) This is called when the last instance of your App Widget is deleted from the App Widget host. This is where you should clean up any work
29、done in onEnabled(Context), such as delete a temporary database. onReceive(Context, Intent) This is called for every broadcast and before each of the above callback methods. You normally dont need to implement this method because the default AppWidgetProvider implementation filters all App Widget br
30、oadcasts and calls the above methods as appropriate.Note: In Android 1.5, there is a known issue in which the onDeleted() method will not be called when it should be. To work around this issue, you can implement onReceive() as described in this Group post to receive the onDeleted() callback.The most
31、 important AppWidgetProvider callback is onUpdated() because it is called when each App Widget is added to a host (unless you use a configuration Activity). If your App Widget accepts any user interaction events, then you need to register the event handlers in this callback. If your App Widget doesn
32、t create temporary files or databases, or perform other work that requires clean-up, then onUpdated() may be the only callback method you need to define. For example, if you want an App Widget with a button that launches an Activity when clicked, you could use the following implementation of AppWidg
33、etProvider:public class ExampleAppWidgetProvider extends AppWidgetProvider public void onUpdate(Context context, AppWidgetManager appWidgetManager, int appWidgetIds) final int N = appWidgetIds.length; / Perform this loop procedure for each App Widget that belongs to this provider for (int i=0; i Bro
34、adcast Receiver Lifecycle for more information). If your App Widget setup process can take several seconds (perhaps while performing web requests) and you require that your process continues, consider starting a Service in the onUpdated() method. From within the Service, you can perform your own upd
35、ates to the App Widget without worrying about the AppWidgetProvider closing down due to an Application Not Responding (ANR) error. See the Wiktionary samples AppWidgetProvider for an example of an App Widget running a Service.Also see the ExampleAppWidgetProvider.java sample class.Receiving App Widg
36、et broadcast IntentsAppWidgetProvider is just a convenience class. If you would like to receive the App Widget broadcasts directly, you can implement your own BroadcastReceiver or override the onReceive(Context, Intent) callback. The four Intents you need to care about are : ACTION_APPWIDGET_UPDATE
37、ACTION_APPWIDGET_DELETED ACTION_APPWIDGET_ENABLED ACTION_APPWIDGET_DISABLEDCreating an App Widget Configuration ActivityIf you would like the user to configure settings when he or she adds a new App Widget, you can create an App Widget configuration Activity. This Activity will be automatically laun
38、ched by the App Widget host and allows the user to configure available settings for the App Widget at create-time, such as the App Widget color, size, update period or other functionality settings.The configuration Activity should be declared as a normal Activity in the Android manifest file. Howeve
39、r, it will be launched by the App Widget host with the ACTION_APPWIDGET_CONFIGURE action, so the Activity needs to accept this Intent. For example: Also, the Activity must be declared in the AppWidgetProviderInfo XML file, with the android:configure attribute (see Adding the AppWidgetProvierInfo Metadata above). For example, the configuration Activity can be declared like this:Notice that the Activity is declared with a fully-qualified namespace, because it will be referenced from outside your package scope.