Fix BottomNavigationDrawerCallback jumping slideOffset on first open.

- Added method to calculate the bottomsheet offset when half expanded before being able to receive it in onStateChanged
- Update to use MDC's addBottomSheetCallback method

Change-Id: I8463b5e42901900aae908474e3d56660c57a85ba

Author: hunterstich

app/src/main/java/com/materialstudies/reply/ui/nav/BottomNavDrawerFragment.kt

@@ -23,7 +23,6 @@ import android.view.LayoutInflater
 import android.view.View
 import android.view.ViewGroup
 import android.widget.FrameLayout
-import androidx.appcompat.content.res.AppCompatResources
 import androidx.fragment.app.Fragment
 import androidx.lifecycle.observe
 import com.google.android.material.bottomsheet.BottomSheetBehavior
@@ -194,7 +193,7 @@ class BottomNavDrawerFragment :
 
             profileImageView.setOnClickListener { toggleSandwich() }
 
-            behavior.setBottomSheetCallback(bottomSheetCallback)
+            behavior.addBottomSheetCallback(bottomSheetCallback)
             behavior.state = STATE_HIDDEN
 
             val adapter = NavigationAdapter(this@BottomNavDrawerFragment)

app/src/main/java/com/materialstudies/reply/ui/nav/BottomNavigationDrawerCallback.kt

@@ -17,8 +17,12 @@
 package com.materialstudies.reply.ui.nav
 
 import android.view.View
+import androidx.coordinatorlayout.widget.CoordinatorLayout
+import androidx.core.view.doOnNextLayout
+import com.google.android.material.R
 import com.google.android.material.bottomsheet.BottomSheetBehavior
 import com.materialstudies.reply.util.normalize
+import kotlin.math.max
 
 /**
  * A [BottomSheetBehavior.BottomSheetCallback] which helps break apart clients who would like to
@@ -30,17 +34,19 @@ import com.materialstudies.reply.util.normalize
  * in [onSlide] is corrected to guarantee that the offset 0.0 <i>always</i> be exactly at the
  * [BottomSheetBehavior.STATE_HALF_EXPANDED] state.
  */
-class BottomNavigationDrawerCallback : BottomSheetBehavior.BottomSheetCallback() {
+class BottomNavigationDrawerCallback() : BottomSheetBehavior.BottomSheetCallback() {
 
     private val onSlideActions: MutableList<OnSlideAction> = mutableListOf()
     private val onStateChangedActions: MutableList<OnStateChangedAction> = mutableListOf()
 
     private var lastSlideOffset = -1.0F
-    private var halfExpandedSlideOffset = 0.0F
+    private var halfExpandedSlideOffset = Float.MAX_VALUE
 
     override fun onSlide(sheet: View, slideOffset: Float) {
-        lastSlideOffset = slideOffset
+        if (halfExpandedSlideOffset == Float.MAX_VALUE)
+            calculateInitialHalfExpandedSlideOffset(sheet)
 
+        lastSlideOffset = slideOffset
         // Correct for the fact that the slideOffset is not zero when half expanded
         val trueOffset = if (slideOffset <= halfExpandedSlideOffset) {
             slideOffset.normalize(-1F, halfExpandedSlideOffset, -1F, 0F)
@@ -60,6 +66,37 @@ class BottomNavigationDrawerCallback : BottomSheetBehavior.BottomSheetCallback()
         onStateChangedActions.forEach { it.onStateChanged(sheet, newState) }
     }
 
+    /**
+     * Calculate the onSlideOffset which will be given when the bottom sheet is in the
+     * [BottomSheetBehavior.STATE_HALF_EXPANDED] state.
+     *
+     * Recording the correct slide offset for the half expanded state happens in [onStateChanged].
+     * Since the first time the sheet is opened, we haven't yet received a call to [onStateChanged],
+     * this method is used to calculate the initial value manually so we can smoothly normalize
+     * slideOffset values received between -1 and 1.
+     *
+     * See:
+     * [BottomSheetBehavior.calculateCollapsedOffset]
+     * [BottomSheetBehavior.calculateHalfExpandedOffset]
+     * [BottomSheetBehavior.dispatchOnSlide]
+     */
+    private fun calculateInitialHalfExpandedSlideOffset(sheet: View) {
+        val parent = sheet.parent as CoordinatorLayout
+        val behavior = BottomSheetBehavior.from(sheet)
+
+        val halfExpandedOffset = parent.height * (1 - behavior.halfExpandedRatio)
+        val peekHeightMin = parent.resources.getDimensionPixelSize(
+            R.dimen.design_bottom_sheet_peek_height_min
+        )
+        val peek = max(peekHeightMin, parent.height - parent.width * 9 / 16)
+        val collapsedOffset = max(
+            parent.height - peek,
+            max(0, parent.height - sheet.height)
+        )
+        halfExpandedSlideOffset =
+            (collapsedOffset - halfExpandedOffset) / (parent.height - collapsedOffset)
+    }
+
     fun addOnSlideAction(action: OnSlideAction): Boolean {
         return onSlideActions.add(action)
     }

app/src/main/java/com/materialstudies/reply/ui/nav/OnSlideAction.kt

@@ -45,7 +45,6 @@ interface OnSlideAction {
             toInclusive = true
         ) slideOffset: Float
     )
-
 }
 
 /**

app/src/main/res/layout/fragment_bottom_nav_drawer.xml

@@ -43,7 +43,6 @@
             app:behavior_skipCollapsed="true"
             app:behavior_halfExpandedRatio="0.6">
 
-
             <androidx.recyclerview.widget.RecyclerView
                 android:id="@+id/account_recycler_view"
                 android:layout_width="match_parent"