问题
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?
回答1:
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
回答2:
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.
回答3:
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