Input compatibility on large screens

On large screen devices, users more often interact with apps using a keyboard, mouse, trackpad, stylus, or gamepad. To enable your app to accept input from external devices, do the following:

• Test basic keyboard support such as Tab and arrow key keyboard navigation, Enter key text entry confirmation, and Space bar play/pause in media apps
• Add standard keyboard shortcuts where applicable; for example, Ctrl + Z for undo and Ctrl + S for save
• Test basic mouse interactions in the manner of right-click for context menu, icon changes on hover, and mouse wheel or trackpad scroll events on custom views
• Test app-specific input devices such as a stylus for drawing apps, game controllers for games, and MIDI controllers for music apps
• Consider advanced input support that could make the app stand out in desktop environments; for example, touchpad as a cross-fader for DJ apps, mouse capture for games, and extensive keyboard shortcuts for keyboard‑centric users

Keyboard

The way your app responds to keyboard input contributes to a good large screen experience. There are three kinds of keyboard input: navigation, keystrokes, and shortcuts.

Navigation

Keyboard navigation is rarely implemented in touch-centric apps, but users expect it when they are using an app and have their hands on a keyboard. It can also be essential for users with accessibility needs on phones, tablets, foldables, and desktop devices.

For many apps, simple arrow key and tab navigation is all that is needed and is mostly handled automatically by the Android framework. For example, a view of a Button is focusable by default, and keyboard navigation should generally work without any additional code. To enable keyboard navigation for views that are not focusable by default, developers should mark them as focusable, which can be done programmatically or in XML, as shown below. See Focus Handling for more information.

yourView.isFocusable = true

yourView.setFocusable(true);

Alternatively you can set the focusable attribute in your layout file:

android:focusable="true"

Once focus is enabled, the Android framework creates a navigational mapping for all focusable views based on their position. This usually works as expected and no further work is needed. When the default mapping is not correct for an app's needs, it can be overridden as follows:

// Arrow keys
yourView.nextFocusLeftId = R.id.view_to_left
yourView.nextFocusRightId = R.id.view_to_right
yourView.nextFocusTopId = R.id.view_above
yourView.nextFocusBottomId = R.id.view_below

// Tab key
yourView.nextFocusForwardId = R.id.next_view

// Arrow keys
yourView.setNextFocusLeftId(R.id.view_to_left);
yourView.setNextFocusRightId(R.id.view_to_left);
yourView.setNextFocusTopId(R.id.view_to_left);
yourView.setNextFocusBottomId(R.id.view_to_left);

// Tab key
yourView.setNextFocusForwardId(R.id.next_view);

It is good practice to try to access every piece of your app's functionality before each release using the keyboard only. It should be easy to access the most common actions without mouse or touch input.

Remember, keyboard support might be essential for users with accessibility needs.

Keystrokes

For text input that would be handled by an on screen virtual keyboard (IME) such as an EditText, apps should behave as expected on large screen devices with no additional work from the developer. For keystrokes that cannot be anticipated by the framework, apps need to handle the behavior themselves. This is especially true for apps with custom views.

Some examples are chat apps that use the enter key to send a message, media apps that start and stop playback with the space key, and games that control movement with the w, a, s, and d keys.

Most apps override the onKeyUp() callback and add the expected behavior for each received keycode, as shown below:

override fun onKeyUp(keyCode: Int, event: KeyEvent): Boolean {
    return when (keyCode) {
        KeyEvent.KEYCODE_ENTER -> {
            sendChatMessage()
            true
        }
        KeyEvent.KEYCODE_SPACE -> {
            playOrPauseMedia()
            true
        }
        else -> super.onKeyUp(keyCode, event)
    }
}

@Override
public boolean onKeyUp(int keyCode, KeyEvent event) {
    if (keyCode == KeyEvent.KEYCODE_ENTER) {
        sendMessage();
        return true;
    } else if (KeyEvent.KEYCODE_SPACE){
        playOrPauseMedia();
        return true;
    } else {
        return super.onKeyUp(keyCode, event);
    }
}

An onKeyUp event occurs when a key is released. Using this callback prevents apps from needing to process multiple onKeyDown events if a key is held down or released slowly. Games and apps that want to know the moment a key is pressed or that expect users to hold down keyboard keys can look for the onKeyDown() event and handle the repeated onKeyDown events themselves.

For more information on providing keyboard support, see Handle keyboard actions.

Shortcuts

Common Ctrl, Alt, and Shift-based shortcuts are expected when using a hardware keyboard. If an app does not implement them, the experience can feel frustrating to users. Advanced users also appreciate shortcuts for frequently used app-specific tasks. Shortcuts make an app easier to use and differentiate it from apps that don't have shortcuts.

Some common shortcuts include Ctrl + S (save), Ctrl + Z (undo), and Ctrl + Shift + Z (redo). For an example of some more advanced shortcuts, see the list of VLC Media Player shortcut keys.

Shortcuts can be implemented using dispatchKeyShortcutEvent(). This intercepts all meta-key combinations (Alt, Ctrl, and Shift) for a given keycode. To check for a specific meta-key, use KeyEvent.isCtrlPressed(), KeyEvent.isShiftPressed(), KeyEvent.isAltPressed(), or KeyEvent.hasModifiers().

Separating shortcut code from other keystroke handling (such as onKeyUp() and onKeyDown()) can make code maintenance easier and enables the default acceptance of meta-keys without having to manually implement meta-key checks in every case. Allowing all meta-key combinations can also be more convenient for users who are accustomed to different keyboard layouts and operating systems.

override fun dispatchKeyShortcutEvent(event: KeyEvent): Boolean {
  return when (event.keyCode) {
    KeyEvent.KEYCODE_O -> {
      openFile() // Ctrl+O, Shift+O, Alt+O
      true
    }
    KeyEvent.KEYCODE_Z-> {
      if (event.isCtrlPressed) {
        if (event.isShiftPressed) {
          redoLastAction() // Ctrl+Shift+Z pressed
          true
        } else {
          undoLastAction() // Ctrl+Z pressed
          true
        }
      }
    }
    else -> {
      return super.dispatchKeyShortcutEvent(event)
    }
  }
}

@Override
public boolean dispatchKeyShortcutEvent(KeyEvent event) {
  if (event.getKeyCode() == KeyEvent.KEYCODE_O) {
      openFile(); // Ctrl+O, Shift+O, Alt+O
      return true;
  } else if(event.getKeyCode() == KeyEvent.KEYCODE_Z) {
      if (event.isCtrlPressed()) {
          if (event.isShiftPressed()) {
              redoLastAction();
              return true;
          }
          else {
              undoLastAction();
              return true;
          }
      }
  }
  return super.dispatchKeyShortcutEvent(event);
}

You can also implement shortcuts in onKeyUp() by checking for KeyEvent.isCtrlPressed(), KeyEvent.isShiftPressed(), or KeyEvent.isAltPressed() in the same manner as above. This can be easier to maintain if the meta-behavior is more of a modification to an app behavior than a shortcut. For example, when W means "walk forward" and Shift + W means "run forward".

override fun onKeyUp(keyCode: Int, event: KeyEvent): Boolean {
  return when(keyCode) {
    KeyEvent.KEYCODE_W-> {
      if (event.isShiftPressed) {
        if (event.isCtrlPressed) {
          flyForward() // Ctrl+Shift+W pressed
          true
        } else {
          runForward() // Shift+W pressed
          true
        }
      } else {
        walkForward() // W pressed
        true
      }
    }
    else -> super.onKeyUp(keyCode, event)
  }
}

@Override
public boolean onKeyUp(int keyCode, KeyEvent event) {
    if (keyCode == KeyEvent.KEYCODE_W) {
        if (event.isShiftPressed()) {
            if (event.isCtrlPressed()) {
                flyForward(); // Ctrl+Shift+W pressed
                return true;
            } else {
                runForward(); // Shift+W pressed
                return true;
            }
        } else {
            walkForward();
            return true;
        }
    }
    return super.onKeyUp(keyCode, event);
}

Stylus

Many large screen devices come with a stylus, and Android apps handle that as touchscreen input. Some devices might also have a USB or Bluetooth drawing table, like the Wacom Intuos. Android apps can receive bluetooth input, but won't work with USB input.

A stylus event is reported as a touchscreen event via View.onTouchEvent() or View.onGenericMotionEvent(), and contains a MotionEvent.getSource() of type SOURCE_STYLUS.

The MotionEvent will also contain additional data:

• MotionEvent.getToolType() returns TOOL_TYPE_FINGER, TOOL_TYPE_STYLUS, or TOOL_TYPE_ERASER depending on the tool that made contact with the surface
• MotionEvent.getPressure() reports the physical pressure applied to the stylus pen (if supported)
• MotionEvent.getAxisValue() with MotionEvent.AXIS_TILT and MotionEvent.AXIS_ORIENTATION which can be used to read the physical tilt and orientation of the stylus (if supported)

Historical points

Android batches input events and delivers them once per frame. A stylus pen can report events at much higher frequencies than the display. When creating drawing apps, it is important to check for events that may be in the recent past by using the getHistorical APIs:

• MotionEvent.getHistoricalX()
• MotionEvent.getHistoricalY()
• MotionEvent.getHistoricalPressure()
• MotionEvent.getHistoricalAxisValue()

Palm rejection

Most large screen devices attempt to recognize when a user's palm is resting on the touchscreen. However, this is not always possible. Sometimes a touch event might be reported to the app before the OS recognizes it as a palm. In that case, touches are canceled by reporting an ACTION_CANCEL event.

This event tells the app that certain touches are invalid and it should undo all interactions caused by those touches. For example, a drawing app might temporarily draw new lines as soon as they are received to provide the lowest latency, but only commit them permanently to the canvas once the touch series is finished cleanly. If touch events are canceled in the meantime, the temporary lines can be easily erased.

Note-taking apps

Chrome OS has a special intent that surfaces registered note-taking apps to users. To register an app as a note-taking app, add the following to the Android manifest:

<intent-filter>
    <action android:name="org.chromium.arc.intent.action.CREATE_NOTE" />
    <category android:name="android.intent.category.DEFAULT" />
</intent-filter>

When an app is registered, the user can select it as the default note-taking app. When a new note is requested, the app should create an empty note ready for stylus input. When the user wishes to annotate an image (such as a screenshot or downloaded image), the app launches with ClipData containing one or more items with content:// URIs. The app should create a note that uses the first attached image as a background image and enter a mode where the user can draw on the screen with a stylus.

Test note-taking intents without a stylus

To test if an app responds correctly to note-taking intents without an active stylus, use the following method to display the note-taking options on Chrome OS:

1. Switch to dev mode and make the device writable
2. Press Ctrl + Alt + F2 to open a terminal
3. Run the command sudo vi /etc/chrome_dev.conf
4. Press i to edit and add --ash-enable-palette to a new line at the end of the file
5. Save by pressing Esc and then typing :, w, q and pressing Enter
6. Press Ctrl + Alt + F1 to return to the regular Chrome OS UI
7. Log out and back in

There should now be a stylus menu on the shelf:

• Tap the stylus button on the shelf and choose New note. This should open a blank drawing note.
• Take a screenshot. From the shelf, select stylus button > Capture screen or download an image. There should be the option to "Annotate image" in the notification. This should launch the app with the image ready to be annotated.

Mouse and touchpad support

Most apps generally only need to handle three large screen–centric events: right-click, hover, and drag and drop.

Right-click

Any actions that cause an app to show a context menu, like touch & hold on a list item, should also react to right-click events. To handle right-click events, apps should register a View.OnContextClickListener. For details on constructing a context menu, see Creating Contextual Menus.

yourView.setOnContextClickListener {
  showContextMenu()
  true
}

yourView.setOnContextClickListener(v -> {
    showContextMenu();
    return true;
});

Hover

Developers can make their app layouts feel polished and easier to use by handling hover events. This is especially true for custom views. The two most common examples of this are:

• Indicating to users if an element has interactive behavior, such as being clickable or editable, by changing the mouse pointer icon
• Adding visual feedback to items in a large list or grid when the pointer is hovering over them

// Change the icon to a "hand" pointer on hover,
// Highlight the view by changing the background.
yourView.setOnHoverListener { view, _ ->
  addVisualHighlighting(true)
  view.pointerIcon =
    PointerIcon.getSystemIcon(view.context,
    PointerIcon.TYPE_HAND)
  false // listener did not consume the event.
}

yourView.setOnHoverListener((view, event) -> {
    addVisualHighlighting(true);
    view.setPointerIcon(PointerIcon
            .getSystemIcon(view.getContext(), PointerIcon.TYPE_HAND));
    return true;
});

Drag and drop

In a multi-window environment, users expect to be able to drag and drop items between apps. This is true for desktop devices as well as tablets, phones, and foldables in split-screen mode.

Developers should consider whether users are likely to drag items into their app. Some common examples include: photo editors should expect to receive photos, audio players should expect to receive audio files, and drawing programs should expect to receive photos.

To add drag and drop support, follow the Android Drag and drop documentation and take a look at this Chrome OS blog post.

Special considerations for Chrome OS

• Remember to request permission via requestDragAndDropPermissions to access items dragged in from outside the app
• An item must have the View.DRAG_FLAG_GLOBAL flag in order to be dragged out to other applications

Advanced pointer support

Apps that do advanced handling of mouse and touchpad input should follow the Android documentation for View.onGenericMotionEvent() and use MotionEvent.getSource() to distinguish between SOURCE_MOUSE and SOURCE_TOUCHSCREEN.

Examine the MotionEvent to implement the required behavior:

• Movement generates ACTION_HOVER_MOVE events.
• Buttons generate ACTION_BUTTON_PRESS and ACTION_BUTTON_RELEASE events. You can also check the current state of all mouse/trackpad buttons using getButtonState().
• Mouse wheel scrolling generates ACTION_SCROLL events.

Game controllers

Some large screen Android devices support up to four game controllers. Developers should use the standard Android game controller APIs to handle them (see Support game controllers).

Buttons are mapped to common values following a common mapping. Unfortunately, not all game controller manufacturers follow the same mapping conventions. You can provide a much better experience if you allow users to select different popular controller mappings. See Process gamepad button presses for more information.

Input translation mode

Chrome OS enables an input translation mode by default. For most Android apps this mode helps apps work as expected in a desktop environment. Some examples include automatically enabling two-finger scrolling on the touchpad, mouse wheel scrolling, and mapping raw display coordinates to window coordinates. Generally, app developers do not need to implement any of these behaviors themselves.

If an app implements custom input behavior, for example defining a custom two-finger touchpad pinch action, or these input translations do not provide the input events expected by the app, you can disable the input translation mode by adding the following tag to the Android manifest:

<uses-feature
    android:name="android.hardware.type.pc"
    android:required="false" />

Additional resources

• Input compatibility