Vertical ViewPager and Android Pie Inconsistent Behavior with Swipe Gesture

Question

My problem is closely related to two other questions that haven\'t been answered yet.

ViewPager not responding to touch in layout area created dynamically in Fragmen

Answer 1

The problem seems to be in the way #swapXY exchanges the x and y values. I believe that the VelocityTracker used in ViewPager uses #getAxisValue and not #getX/#getY, and the result is not swapped. But there doesn't seem to be a way to set the axis values nor to subclass MotionEvent so I didn't find a way to stick with the simple #swapXY solution. I forked ViewPager and use VelocityTracker.getYVelocity when I detect the unswapped condition.

diff --git project/src/main/java/org/gc/project/util/ShopVerticalViewPager.java project/src/main/java/org/gc/project/util/ShopVerticalViewPager.java
index e5560a0..f23f9f7 100644
--- project/src/main/java/org/gc/project/util/MyVerticalViewPager.java
+++ project/src/main/java/org/gc/project/util/MyVerticalViewPager.java
@@ -179,4 +179,8 @@ public class ShopVerticalViewPager extends ViewPager {
return super.onTouchEvent( swapXY( ev ) );
}

+ public boolean isVerticalMode() {
+ return true;
+ }
+
}
\ No newline at end of file
diff --git project/src/main/java/gcandroid/support/v4/view/ViewPager.java project/src/main/java/gcandroid/support/v4/view/ViewPager.java
index 20e1448..4ae2d3c 100644
--- project/src/main/java/gcandroid/support/v4/view/ViewPager.java
+++ project/src/main/java/gcandroid/support/v4/view/ViewPager.java
@@ -205,6 +205,7 @@ public class ViewPager extends ViewGroup {
private int mMaximumVelocity;
private int mFlingDistance;
private int mCloseEnough;
+ private boolean mInvertedVelocityTrackerInVerticalMode = false;

// If the pager is at least this close to its final position, complete the scroll
// on touch down and let the user interact with the content inside instead of
@@ -391,6 +392,21 @@ public class ViewPager extends ViewGroup {
ViewCompat.setImportantForAccessibility(this,
ViewCompat.IMPORTANT_FOR_ACCESSIBILITY_YES);
}
+
+ // tell if the velocity tracker is inverted in vertical mode (most probably uses MotionEvent.getAxisValue instead of MotionEvent.getX but
+ // I can't change these values nor inherit from MotionEvent)
+ VelocityTracker vt = VelocityTracker.obtain();
+ long time = SystemClock.uptimeMillis();
+ MotionEvent ev = MotionEvent.obtain(time, time, MotionEvent.ACTION_DOWN, 0, 0, 0);
+ vt.addMovement(ev);
+ ev.recycle();
+ ev = MotionEvent.obtain(time, time + 10, MotionEvent.ACTION_MOVE, 10, 0, 0);
+ ev.setLocation( 0, 10 );
+ vt.addMovement(ev);
+ ev.recycle();
+ vt.computeCurrentVelocity(1000, mMaximumVelocity);
+ mInvertedVelocityTrackerInVerticalMode = vt.getYVelocity() == 0;
+ vt.recycle();
}

@Override
@@ -2027,6 +2043,10 @@ public class ViewPager extends ViewGroup {
return mIsBeingDragged;
}

+ public boolean isVerticalMode() {
+ return false;
+ }
+
@Override
public boolean onTouchEvent(MotionEvent ev) {
if (mFakeDragging) {
@@ -2111,8 +2131,9 @@ public class ViewPager extends ViewGroup {
if (mIsBeingDragged) {
final VelocityTracker velocityTracker = mVelocityTracker;
velocityTracker.computeCurrentVelocity(1000, mMaximumVelocity);
- int initialVelocity = (int) VelocityTrackerCompat.getXVelocity(
- velocityTracker, mActivePointerId);
+ int initialVelocity = (int) ( isVerticalMode() && mInvertedVelocityTrackerInVerticalMode ? VelocityTrackerCompat.getYVelocity( velocityTracker, mActivePointerId )
+ : VelocityTrackerCompat.getXVelocity( velocityTracker, mActivePointerId ) );
+
mPopulatePending = true;
final int width = getClientWidth();
final int scrollX = getScrollX();