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Window management

Chrome OS supports Android apps in multiple windows. The system renders apps into window containers whose size is determined by the form factor of the device, as shown in Figure 1.

Figure 1: An app window on different devices

Resizing windows

In Chrome OS users can resize an app's window in the usual way, by dragging the lower right corner, as shown in Figure 2.

Figure 2: A resizable app window

There are two options for handling window resizing:

  • Respond to configuration changes dynamically by calling onConfigurationChanged(..) and adding, for example, android:configChanges="screenSize|smallestScreenSize|orientation|screenLayout" to the activity's manifest. Read handling configuration change docs for more information about handling configuration changes.
  • Let the system restart the activity. In this case you should implement onSaveInstanceState and use the ViewModel architecture component to restore the previous saved state.

This page shows how to ensure your app's window launches correctly, resizes smoothly, and can display all of its contents when its size changes.

Window dimensions

An activity should read its window dimensions every time it starts, and arrange its content according to the current configuration.

To determine the current configuration, call getResources().getConfiguration() on the current activity. Do not use the configuration of the background activity or the system resource. The background activity does not have a size, and the system configuration may contain multiple windows with conflicting sizes and orientations, so no usable data can be extracted.

Note that the window size and the screen size are not the same. To get the window size in DP, use Activity.getResources().getConfiguration().screenWidth and Activity.getResources().getConfiguration().screenHeight. You probably never need to use the screen size.

Content bounds

A window's content bounds can change upon resizing. For example, the area within the window that is used by the app can change if the window becomes too big to fit on the screen. Follow these guidelines:

  • Apps that use Android's layout process are automatically laid out in the available space.

  • Native apps should read the available area and monitor size changes to avoid having inaccessible UI elements. Call the following methods to determine the initial available size for this surface:

    • NativeActivity.mLastContent[X/Y/Width/Height]()
    • findViewById(android.R.id.content).get[Width/Height]()

    Continuous monitoring can be done via observer:

    • NativeActivity.onContentRectChangedNative()
    • NativeActivity.onGlobalLayout()
    • Add a listener to view.addOnLayoutChangeListener(findViewById(android.R.id.content)) If the app is pre-scaling its artwork, it should do this every time the resolution changes.

Free-form resizing

Chrome OS allows any window to be freely resized: the user can change a window's width, height, and position on the screen. Many Android apps are written without free-form resizing in mind. Consider these issues:

  • The screen position might change. Always use the system to perform window-to-screen and screen-to-window coordinate transformations.
  • If you are using Android's view system, your window layout automatically changes when its size changes.
  • If you do not use the view system and take over the surface, your app must handle size changes on its own.
  • Native apps should use the mLastContent members, or use the content view to determine the initial size.
  • When the app is running it should listen to onContentRectChangedNative or onGlobalLayout events to react to size changes.
  • When the app's size changes, it should rescale or reload layouts, artwork and update input areas.

Full screen mode

Full screen mode works the same way as on stock Android. If the window is not covering the full screen, requests for full screening (hiding all system-UI) are ignored. When the app is maximized the normal fullscreen methods, layouts, and functions are performed. This hides the system UI elements (window control bar and the shelf).

Screen orientation

The most common orientation for an Android app is portrait, since that's how most phones are held. While portrait is good for phones, it's terrible for laptops and tablets, where landscape is preferred. To get the best results for your app consider supporting both orientations.

Some Android apps assume that when a device is held in the portrait mode, the rotation value is always Surface.ROTATION_0. This may be true for most Android devices. However, when the app is in a certain ARC mode, the rotation value for the portrait orientation may not be Surface.ROTATION_0.

To get an accurate rotation value while reading the accelerometer or similar sensors, use the Display.getRotation() method and swap the axis accordingly.

The root activity and orientation

A Chromebook window consists of a stack of activity windows. Each window in the stack has the same size and orientation.

Sudden orientation and size changes are confusing in a desktop environment. The Chromebook window manager avoids this in a way that's similar to Android's side by side mode: The activity at the bottom of the stack controls the attributes of all activities above. This can lead to unexpected situations where a newly started activity which is portrait unresizable becomes landscape resizable.

Device mode has an effect here: In tablet mode the orientation is not locked and each window preserves its own orientation as it is normal on Android.

Orientation guidelines

Follow these guidelines for handling orientation:

  • If you support only one orientation, add the information to the manifest so the window manager knows about it before starting the application. When you specify the orientation, also specify the sensor orientations when possible. Chromebooks are often convertibles and upside down apps are annoying.
  • Try to stay with a single selected orientation. Avoid requesting one orientation in the manifest and setting another programmatically later.
  • Be careful changing the orientation based on window size. The user might get stuck in a small portrait-size window, and not be able to return to a larger landscape window.
  • There are window controls in Chrome to toggle between all available layouts. By choosing the correct orientation option, you can ensure that the user has the correct layout upon launching the app. If an app is available in portrait and landscape, it defaults to landscape, if possible. After this option is set, it is remembered on a per-app basis.
  • Try to avoid unnecessary orientation changes. For example, if the activity orientation is PORTRAIT, but the app calls setRequestedOrientation(LANDSCAPE) at runtime, this causes unnecessary window resizing, which is annoying to the user and possibly restarts the app if you cannot handle it. It's better to set the orientation once, for example, in the manifest, and only change it if necessary.

Initial launch size

Apps can specify their initial launch size in the following ways:

  • Use a launch size only in desktop environments. This helps the window manager to give you the proper bounds and orientation. To indicate a preferences when used in desktop mode, add the following meta tags inside the <activity>:

    <meta-data android:name="WindowManagerPreference:FreeformWindowSize"
           android:value="[phone|tablet|maximize]" />
<meta-data android:name="WindowManagerPreference:FreeformWindowOrientation"
           android:value="[portrait|landscape]" />

  • Use static launch bounds. Use <layout> inside the manifest entry of your activity to specify a "fixed" starting size. See this example:

    <layout android:defaultHeight="500dp"
        android:defaultWidth="600dp"
        android:gravity="top|end"
        android:minHeight="450dp"
        android:minWidth="300dp" />

  • Use dynamic launch bounds. An activity can create and use ActivityOptions.setLaunchBounds(Rect) when creating a new activity. By specifying an empty rectangle, your app can be maximized.

Other considerations

Here are some other aspects to consider when working with Android apps in Chrome OS:

  • Don’t call finish() in your activity’s onDestroy method. This causes the app to close upon resize and not restart, assuming your app has to restart.
  • Don’t use window types that aren't compatible, such as TYPE_KEYGUARD and TYPE_APPLICATION_MEDIA.
  • Be sure that an activity restart is fast by caching objects that have been previously allocated.
  • If you do not want the user to resize your app, specify android:resizeableActivity=false in your manifest file.
  • Test your app to ensure that it handles changes in window size appropriately.
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