This chapter is from the book
This chapter is from the book
This chapter is from the book
3.7 AndroidManifest.xml
In this section, you’ll modify the AndroidManifest.xml file to specify that this app’s Activity supports only a device’s portrait orientation and that the virtual keyboard should always be displayed when the Activity first appears on the screen or navigates back to the Activity. To open the manifest, double click AndroidManifest.xml in the Project window’s manifests folder. Figure 3.19 shows the completed manifest with our changes highlighted—the rest of the file was autogenerated by Android Studio when we created the app’s project. We’ll discuss some aspects of the manifest here. For a list of all the elements a manifest may contain, their attributes and their values, visit
http://developer.android.com/guide/topics/manifest/manifest-intro.html
Fig. 3.19 | AndroidManifest.xml contents.
1 <?xml version="1.0" encoding="utf-8"?>
2 <manifest xmlns:android="http://schemas.android.com/apk/res/android"
3 package="com.deitel.tipcalculator" >
4
5 <application
6 android:allowBackup="true"
7 android:icon="@mipmap/ic_launcher"
8 android:label="@string/app_name"
9 android:supportsRtl="true"
10 android:theme="@style/AppTheme" >
11 <activity
12 android:name=".MainActivity"
13 android:label="@string/app_name"
14 android:screenOrientation="portrait"
15 android:windowSoftInputMode="stateAlwaysVisible">
16 <intent-filter>
17 <action android:name="android.intent.action.MAIN" />
18
19 <category android:name="android.intent.category.LAUNCHER" />
20 </intent-filter>
21 </activity>
22 </application>
23
24 </manifest>3.7.1 manifest Element
The manifest element (lines 2–24) indicates that this XML file’s contents represent the app’s manifest. This element’s package attribute specifies the app’s Java package name that was configured when you created the app’s project (Section 3.4.2). Recall that for apps you submit to the Google Play store, the package name is used as the app’s unique identifier.
3.7.2 application Element
The manifest element’s nested application element (lines 5–21) specifies attributes of the application, including
- android:allowBackup—Whether or not the app’s data should be backed up automatically by Android so that the data can be restored to the device or a new device at a later time.
- android:icon—The app icon that you touch in the launcher to execute the app.
- android:label—The app’s name that’s typically displayed below the icon in the launcher and often displayed in the app bar when the app is executing.
- android:supportsRtl—Whether or not the app’s interface can be flipped horizontally to support right-to-left languages like Arabic and Hebrew.
- android:theme—The theme that determines the default look-and-feel of the app’s views.
Elements nested in the application element define the app’s components, such as its activities.
3.7.3 activity Element
The application element’s nested activity element (lines 10–20) describes an Activity. An app can have many activities, one of which is designated as the Activity that’s displayed when the user touches the app’s icon in the launcher to execute the app. Each activity element specifies at least the following attributes:
- android:name—The Activity’s class name. The notation ".MainActivity" is shorthand for "com.deitel.MainActivity" (where com.deitel is the reverse of the domain name you specified when creating the app’s project).
- android:label—The Activity’s name. This is often displayed in the app bar when the Activity is on the screen. For single Activity apps, this name is typically the same as the app’s name.
For MainActivity, we added the following attributes:
- android:screenOrientation—In general, most apps should support both portrait and landscape orientations. In portrait orientation, the device’s longer dimension is vertical. In landscape orientation, the device’s longer dimension is horizontal. In the Tip Calculator app, rotating the device to landscape orientation on a typical phone would cause the numeric keypad to obscure most of the Tip Calculator’s GUI. For this reason, we set this property to "portrait" to support only portrait orientation.
- android:windowSoftInputMode—In the Tip Calculator app, the soft keypad should be displayed immediately when the app executes and should reappear each time the user returns to the Tip Calculator app. For this reason we set this property to "stateAlwaysVisible". This will not display the soft keyboard if a hard keyboard is present.
3.7.4 intent-filter Element
Intents are Android’s mechanism for communicating between executable components—such as activities, background services and the operating system. You state your intent, then Android uses intent messaging to coordinate the executable components to accomplish what you intend to do. This loose coupling makes it easy to mix and match parts of different applications. You tell Android what you want to accomplish, then let Android find the installed applications with activities that can handle the task.
Inter-App Communication
One example of how Intents are used is coordinating efforts between separate apps. Consider how photo sharing can be handled in Android:
- Most social-networking Android apps provide their own photo-sharing capabilities. Each app can advertise in its manifest its specific Activity that uploads a photo to the user’s account.
- Other apps can use these photo-sharing capabilities, rather than implementing their own. For example, a photo-editing app can provide a Share Photo option. The app can respond to a user’s photo-sharing request by stating its intent to share a photo—that is, creating a photo-sharing Intent and passing it to Android.
- Android looks at the Intent to determine which installed applications provide activities that can share photos.
- If there’s only one such app, Android executes that app’s photo-sharing Activity.
- If there are many such apps, Android displays a list of apps and asks the user to decide which app’s photo-sharing Activity should execute.
A key benefit of this loosely coupled approach is that the photo-editing app’s developer does not need to incorporate support for every possible social-networking site. By issuing a photo-sharing Intent, the app automatically supports any app that declares a photo-sharing Activity in its manifest, including those apps the user has already installed and any the user chooses to install in the future. For a list of the items that can be used with Intents, visit
http://developer.android.com/reference/android/content/Intent.html#constants
Executing Apps
Another example of how Intents are used is in launching activities. When you touch an app’s icon in the device’s launcher app, your intent is to execute the app. In this case, the launcher issues an Intent to execute that app’s main Activity (discussed momentarily). Android responds to this Intent by launching the app and executing the specific Activity designated in the app’s manifest as the main Activity.
Determining Which Activity to Execute
Android uses information in the manifest to determine the activities that can respond to Intents and which Intents each Activity can handle. In the manifest, the activity element’s nested intent-filter element (Fig. 3.19, lines 16–20) determines which Intent types can launch an Activity. If an Intent matches only one Activity’s intent-filter, Android executes that Activity. If there are multiple matches, Android presents a list from which the user can choose an app, then executes the appropriate Activity in that app.
Android also passes the Intent to the Activity, because an Intent often contains data the Activity can use to perform its task. For example, a photo-editing app can include in a share-photo Intent the specific photo to share.
The intent-filter element must contain one or more action elements. The action "android.intent.action.MAIN" in line 17 of Fig. 3.19 indicates that MainActivity is the Activity to execute when the app launches. The optional category element in line 19 specifies what initiates the Intent—for "android.intent.category.LAUNCHER", it’s the device’s launcher. This category also indicates that the Activity should appear as an icon in the device’s launcher with the icons for the user’s other installed apps.
We’ll discuss and program with Intents in the next chapter. For more information on Intents and Intent filters, visit
http://developer.android.com/guide/components/intents-filters.html