RecyclerView Scrollbar is easier to target

Bug: 191666122
Test: manual

TL;DR;;
1) Allow some x offset when determining touch points are hitting the track
2) reduce the timeout to consider dragging state

Change-Id: Iebcbbbd1e50b602119795c57fc04c4c2a5ccdde5

src/com/android/launcher3/views/RecyclerViewFastScroller.java

@@ -18,6 +18,8 @@ package com.android.launcher3.views;
 
 import static android.view.HapticFeedbackConstants.CLOCK_TICK;
 
+import static androidx.recyclerview.widget.RecyclerView.SCROLL_STATE_IDLE;
+
 import android.animation.ObjectAnimator;
 import android.content.Context;
 import android.content.res.Resources;
@@ -30,6 +32,7 @@ import android.graphics.Rect;
 import android.graphics.RectF;
 import android.os.Build;
 import android.util.AttributeSet;
+import android.util.Log;
 import android.util.Property;
 import android.view.MotionEvent;
 import android.view.View;
@@ -54,9 +57,14 @@ import java.util.List;
  * The track and scrollbar that shows when you scroll the list.
  */
 public class RecyclerViewFastScroller extends View {
-
-    private static final int FASTSCROLL_THRESHOLD_MILLIS = 200;
+    private static final String TAG = "RecyclerViewFastScroller";
+    private static final boolean DEBUG = false;
+    private static final int FASTSCROLL_THRESHOLD_MILLIS = 40;
     private static final int SCROLL_DELTA_THRESHOLD_DP = 4;
+
+    // Track is very narrow to target and correctly. This is especially the case if a user is
+    // using a hardware case. Even if x is offset by following amount, we consider it to be valid.
+    private static final int SCROLLBAR_LEFT_OFFSET_TOUCH_DELEGATE_DP = 5;
     private static final Rect sTempRect = new Rect();
 
     private static final Property<RecyclerViewFastScroller, Integer> TRACK_WIDTH =
@@ -86,6 +94,7 @@ public class RecyclerViewFastScroller extends View {
     /** Keeps the last known scrolling delta/velocity along y-axis. */
     private int mDy = 0;
     private final float mDeltaThreshold;
+    private final float mScrollbarLeftOffsetTouchDelegate;
 
     private final ViewConfiguration mConfig;
 
@@ -157,6 +166,8 @@ public class RecyclerViewFastScroller extends View {
 
         mConfig = ViewConfiguration.get(context);
         mDeltaThreshold = res.getDisplayMetrics().density * SCROLL_DELTA_THRESHOLD_DP;
+        mScrollbarLeftOffsetTouchDelegate = res.getDisplayMetrics().density
+                * SCROLLBAR_LEFT_OFFSET_TOUCH_DELEGATE_DP;
 
         TypedArray ta =
                 context.obtainStyledAttributes(attrs, R.styleable.RecyclerViewFastScroller, defStyleAttr, 0);
@@ -239,6 +250,7 @@ public class RecyclerViewFastScroller extends View {
     public boolean handleTouchEvent(MotionEvent ev, Point offset) {
         int x = (int) ev.getX() - offset.x;
         int y = (int) ev.getY() - offset.y;
+
         switch (ev.getAction()) {
             case MotionEvent.ACTION_DOWN:
                 // Keep track of the down positions
@@ -247,7 +259,7 @@ public class RecyclerViewFastScroller extends View {
                 mDownTimeStampMillis = ev.getDownTime();
 
                 if ((Math.abs(mDy) < mDeltaThreshold &&
-                        mRv.getScrollState() != RecyclerView.SCROLL_STATE_IDLE)) {
+                        mRv.getScrollState() != SCROLL_STATE_IDLE)) {
                     // now the touch events are being passed to the {@link WidgetCell} until the
                     // touch sequence goes over the touch slop.
                     mRv.stopScroll();
@@ -293,6 +305,13 @@ public class RecyclerViewFastScroller extends View {
                 }
                 break;
         }
+        if (DEBUG) {
+            Log.d(TAG, (ev.getAction() == MotionEvent.ACTION_DOWN ? "\n" : "")
+                    + "handleTouchEvent " + MotionEvent.actionToString(ev.getAction())
+                    + " (" + x + "," + y + ")" + " isDragging=" + mIsDragging
+                    + " mIgnoreDragGesture=" + mIgnoreDragGesture);
+
+        }
         return mIsDragging;
     }
 
@@ -401,7 +420,8 @@ public class RecyclerViewFastScroller extends View {
      * Returns whether the specified x position is near the scroll bar.
      */
     public boolean isNearScrollBar(int x) {
-        return x >= (getWidth() - mMaxWidth) / 2 && x <= (getWidth() + mMaxWidth) / 2;
+        return x >= (getWidth() - mMaxWidth) / 2 - mScrollbarLeftOffsetTouchDelegate
+                && x <= (getWidth() + mMaxWidth) / 2;
     }
 
     private void animatePopupVisibility(boolean visible) {