如何在 Android 上指定仅适用于手机或平板电脑的活动

Question

我在查看 Google I/O Session 2012 app 时遇到了这个 TODO

// TODO: use <meta-data> element instead
private static final Class[] sPhoneActivities = new Class[]{
        MapActivity.class,
        SessionDetailActivity.class,
        SessionsActivity.class,
        TrackDetailActivity.class,
        VendorDetailActivity.class,
};

// TODO: use <meta-data> element instead
private static final Class[] sTabletActivities = new Class[]{
        MapMultiPaneActivity.class,
        SessionsVendorsMultiPaneActivity.class,
};

public static void enableDisableActivities(final Context context) {
    boolean isHoneycombTablet = isHoneycombTablet(context);
    PackageManager pm = context.getPackageManager();

    // Enable/disable phone activities
    for (Class a : sPhoneActivities) {
        pm.setComponentEnabledSetting(new ComponentName(context, a),
                isHoneycombTablet
                        ? PackageManager.COMPONENT_ENABLED_STATE_DISABLED
                        : PackageManager.COMPONENT_ENABLED_STATE_ENABLED,
                PackageManager.DONT_KILL_APP);
    }

    // Enable/disable tablet activities
    for (Class a : sTabletActivities) {
        pm.setComponentEnabledSetting(new ComponentName(context, a),
                isHoneycombTablet
                        ? PackageManager.COMPONENT_ENABLED_STATE_ENABLED
                        : PackageManager.COMPONENT_ENABLED_STATE_DISABLED,
                PackageManager.DONT_KILL_APP);
    }
}

这让我想知道如何执行该 TODO。

Answer 1

我想出了这个方法（注意：这是仿照Google I/O Session 2012 appUIUtilis.java）：

在AndroidManifest.xml 中定义Activitys 以包括<meta-data>：

<!-- Note: specify the target device for Activities with target_device meta-data of "universal|phone|tablet"
           see UIUtils.java (configureDeviceSpecificActivities) for more details. -->

<!-- Activities for both phones and tablets -->
<activity android:name=".ui.AccountActivity" 
          android:configChanges="orientation|keyboardHidden" 
          android:label="@string/app_name"
          android:theme="@style/Theme.Accounts">
          <meta-data android:name="target_device" android:value="universal"/>
</activity>

<!-- Activities for tablets -->
<activity android:name=".ui.CoolMultipaneActivity"
          android:label="@string/app_name">
          <meta-data android:name="target_device" android:value="tablet"/>

辛苦都放在方法configureDeviceSpecificActivities(Context context)

/**
 * Enables and disables {@linkplain android.app.Activity activities} based on their "target_device" meta-data and
 * the current device. Add <meta-data name="target_device" value="tablet|phone|universal" /> to an activity to
 * specify its target device.
 * @param context the current context of the device
 * @see #isHoneycombTablet(android.content.Context)
 */
public static void configureDeviceSpecificActivities(Context context) {
    final PackageManager package_manager = context.getPackageManager();
    final boolean is_honeycomb_tablet = isHoneycombTablet(context);
    try {
        final ActivityInfo[] activity_info = package_manager.getPackageInfo(context.getPackageName(),
                PackageManager.GET_ACTIVITIES | PackageManager.GET_META_DATA).activities;
        for (ActivityInfo info : activity_info) {
            final String target_device = info.metaData.getString("target_device");
            if (target_device == null) break;
            target_device = target_device.toLowerCase(Locale.US);
            final boolean is_for_tablet = target_device.equals("tablet");
            final boolean is_for_phone = target_device.equals("phone");
            final String class_name = info.name;
            package_manager.setComponentEnabledSetting(new ComponentName(context, Class.forName(class_name)),
                    is_honeycomb_tablet && is_for_phone
                            ? PackageManager.COMPONENT_ENABLED_STATE_DISABLED
                            : !is_honeycomb_tablet && is_for_tablet
                            ? PackageManager.COMPONENT_ENABLED_STATE_DISABLED
                            : PackageManager.COMPONENT_ENABLED_STATE_ENABLED,
                    PackageManager.DONT_KILL_APP);
        }
    } catch (PackageManager.NameNotFoundException error) {
        Ln.w(error.getCause());
    } catch (ClassNotFoundException error) {
        Ln.w(error.getCause());
    }
}

有趣的事实：如果没有 GET_META_DATA 标志，它将无法工作，因为如果您不包含该标签，metaData 将始终返回 null。

最后一点是调用这个方法，可能在你最初的Activity的onCreate中

@Override
protected void onCreate(Bundle icicle) {
    super.onCreate(icicle);

    // Anything else you want to do in the onCreate callback

    // Set up to use the appropriate Activities for the given device
    UIUtils.configureDeviceSpecificActivities(this);
}

现在您可以拥有专为手机和平板电脑设计的Activitys，以应对仅更改布局并可能包含更多Fragments 还不够的时代。

注意：如果您看到警告，final String class_name = info.packageName + info.name; 可能必须是 final String class_name = info.name;。

注意(2)：final String target_device = info.metaData.getString("target_device", "").toLowerCase(); 应该是为了向后兼容 API 12。

String target_device = info.metaData.getString("target_device");
if (target_device == null) break;
target_device = target_device.toLowerCase();

注意(3)：target_device.toLowerCase(); 隐式使用默认语言环境。请改用target_device.toLowerCase(Locale.US)。并对上面的代码进行了所有修改。