Speaking "ok glass" brings up a command list that automatically scrolls based on the user's head motion.
Is there a built-in UI element in the GDK that implements this? Or will I have to write my own code that uses sensors?
I tried reimplementing parts of this. It's not as shiny as the google one, but those could serve as a starting point:
https://github.com/pscholl/glass_snippets/blob/master/lib/src/main/java/de/tud/ess/HeadListView.java https://github.com/pscholl/glass_snippets/blob/master/lib/src/main/java/de/tud/ess/HeadScrollView.java
I went through the GDK's Developer Guides at https://developers.google.com/glass/develop/gdk/dev-guides and Reference at https://developers.google.com/glass/develop/gdk/reference/index and there's definitely no such built-in UI elements in GDK, as of XE 12 released in December 2013.
So the answer for now is yes you have to use sensors to implement that.
There is currently no native GDK UI element for scrolling a list using sensors (in fact, according to this issue, use of ListView at all appears to be discouraged).
However, I was able to get the following to work reasonably well in my app. My list is fixed at 4 elements (which helps determine how much scrolling happens), so you can tweak this accordingly (see comments).
import com.google.android.glass.media.Sounds;
import com.google.android.glass.touchpad.Gesture;
import com.google.android.glass.touchpad.GestureDetector;
import android.content.Context;
import android.hardware.Sensor;
import android.hardware.SensorEvent;
import android.hardware.SensorEventListener;
import android.hardware.SensorManager;
import android.media.AudioManager;
import android.view.MotionEvent;
import android.widget.ListView;
/**
* Implements sensor-based scrolling of a ListView
*/
public class SensorListController implements SensorEventListener, GestureDetector.BaseListener {
static final String TAG = "SensorListController";
Context mContext;
ListView mList;
SensorManager mSensorManager;
private float[] mRotationMatrix = new float[16];
private float[] mOrientation = new float[9];
private float[] history = new float[2];
private float mHeading;
private float mPitch;
boolean mActive = true;
GestureDetector mGestureDetector;
public SensorListController(Context context, ListView list) {
this.mContext = context;
this.mList = list;
history[0] = 10;
history[1] = 10;
mGestureDetector = new GestureDetector(mContext);
mGestureDetector.setBaseListener(this);
}
/**
* Receive pass-through of event from View
*/
public boolean onMotionEvent(MotionEvent event) {
return mGestureDetector.onMotionEvent(event);
}
@Override
public boolean onGesture(Gesture gesture) {
switch (gesture) {
case TWO_LONG_PRESS:
// Toggle on and off accelerometer control of the list by long press
playSuccessSound();
toggleActive();
return true;
case TWO_TAP:
// Go to top of the list
playSuccessSound();
scrollToTop();
return true;
}
return false;
}
/**
* Should be called from the onResume() of Activity
*/
public void onResume() {
mSensorManager = (SensorManager) mContext.getSystemService(Context.SENSOR_SERVICE);
mSensorManager.registerListener(this,
mSensorManager.getDefaultSensor(Sensor.TYPE_ROTATION_VECTOR),
SensorManager.SENSOR_DELAY_UI);
}
/**
* Should be called from the onPause() of Activity
*/
public void onPause() {
mSensorManager.unregisterListener(this);
}
/**
* Toggles whether the controller modifies the view
*/
public void toggleActive() {
mActive = !mActive;
}
@Override
public void onSensorChanged(SensorEvent event) {
if (mList == null || !mActive) {
return;
}
if (event.sensor.getType() == Sensor.TYPE_ROTATION_VECTOR) {
SensorManager.getRotationMatrixFromVector(mRotationMatrix, event.values);
SensorManager.remapCoordinateSystem(mRotationMatrix, SensorManager.AXIS_X,
SensorManager.AXIS_Z, mRotationMatrix);
SensorManager.getOrientation(mRotationMatrix, mOrientation);
mHeading = (float) Math.toDegrees(mOrientation[0]);
mPitch = (float) Math.toDegrees(mOrientation[1]);
float xDelta = history[0] - mHeading; // Currently unused
float yDelta = history[1] - mPitch;
history[0] = mHeading;
history[1] = mPitch;
float Y_DELTA_THRESHOLD = 0.13f;
// Log.d(TAG, "Y Delta = " + yDelta);
int scrollHeight = mList.getHeight()
/ 19; // 4 items per page, scroll almost 1/5 an item
// Log.d(TAG, "ScrollHeight = " + scrollHeight);
if (yDelta > Y_DELTA_THRESHOLD) {
// Log.d(TAG, "Detected change in pitch up...");
mList.smoothScrollBy(-scrollHeight, 0);
} else if (yDelta < -Y_DELTA_THRESHOLD) {
// Log.d(TAG, "Detected change in pitch down...");
mList.smoothScrollBy(scrollHeight, 0);
}
}
}
@Override
public void onAccuracyChanged(Sensor sensor, int accuracy) {
}
private void scrollToTop() {
mList.smoothScrollToPosition(0);
}
private void playSuccessSound() {
// Play sound to acknowledge action
AudioManager audio = (AudioManager) mContext.getSystemService(Context.AUDIO_SERVICE);
audio.playSoundEffect(Sounds.SUCCESS);
}
}
I used the above in a ListActivity. I initialize it in onCreate(), and here is the method that initializes it:
private void initListController() {
mListView = getListView();
mListView.setChoiceMode(ListView.CHOICE_MODE_NONE);
mListView.setSelector(android.R.color.transparent);
mListView.setClickable(true);
mListController = new SensorListController(this, mListView);
}
This also removes the selection indicator from view by making it transparent.
The above controller also uses two finger press to pause/resume scrolling, and a two finger tap to scroll to the top of the list (and acknowledges both these actions with a sound). Note that for these gestures to work, you will need to override onGenericMotionEvent() in your Activity and pass through the event, like:
@Override
public boolean onGenericMotionEvent(MotionEvent event) {
// We need to pass events through to the list controller
if (mListController != null) {
return mListController.onMotionEvent(event);
}
return false;
}
Full source code for this solution can be seen on Github, and the APK can be downloaded here.
来源：https://stackoverflow.com/questions/21583114/built-in-scrollview-that-scrolls-with-head-motion