Fix the fix to the fix to the recentering algorithm

I had a big brain realisation to use the power of RxJava to make things
work in a clean way that is probably more technically correct than
manually invoking measure and layout.

Author: farewelltospring

app/src/main/java/org/thoughtcrime/securesms/conversation/AttachmentButtonCenterHelper.kt

@@ -1,6 +1,11 @@
 package org.thoughtcrime.securesms.conversation
 
 import android.view.View
+import android.view.View.OnLayoutChangeListener
+import io.reactivex.rxjava3.android.schedulers.AndroidSchedulers
+import io.reactivex.rxjava3.core.Observable
+import io.reactivex.rxjava3.disposables.Disposable
+import io.reactivex.rxjava3.subjects.PublishSubject
 import org.signal.core.util.DimensionUnit
 import org.signal.core.util.logging.Log
 
@@ -11,17 +16,55 @@ import org.signal.core.util.logging.Log
  * then put a basic amount of padding on each side so that it looks nice when scrolling
  * to either end.
  */
-object AttachmentButtonCenterHelper {
+class AttachmentButtonCenterHelper(val buttonHolder: View, val wrapper: View) {
 
-  private val TAG = Log.tag(AttachmentButtonCenterHelper::class)
-  private val DEFAULT_PADDING = DimensionUnit.DP.toPixels(16f).toInt()
+  companion object {
+    val TAG = Log.tag(AttachmentButtonCenterHelper::class)
+    private val DEFAULT_PADDING = DimensionUnit.DP.toPixels(16f).toInt()
+  }
+
+  /** The wrapper width is the maximum size of the button holder before scrollbars appear. */
+  private val wrapperWidthObservable: PublishSubject<Int> = PublishSubject.create()
+  private val emitNewWrapperWidth = OnLayoutChangeListener { _, left, _, right, _, oldLeft, _, oldRight, _ ->
+    if (oldRight - oldLeft == right - left)
+      return@OnLayoutChangeListener
+    wrapperWidthObservable.onNext(right - left)
+  }
+
+  /** The "core width" of the button holder is the size of its contents. */
+  private val coreWidthObservable: PublishSubject<Int> = PublishSubject.create()
+  private val emitNewCoreWidth = OnLayoutChangeListener { view, left, _, right, _, oldLeft, _, oldRight, _ ->
+    val newCoreWidth = view.run { width - (paddingLeft + paddingRight) }
+    coreWidthObservable.onNext(newCoreWidth)
+  }
+
+  private var listener: Disposable? = null
+
+  fun attach() {
+    wrapper.addOnLayoutChangeListener(emitNewWrapperWidth)
+    buttonHolder.addOnLayoutChangeListener(emitNewCoreWidth)
+
+    listener?.dispose()
+    listener = Observable.combineLatest(wrapperWidthObservable, coreWidthObservable, ::Pair)
+      .distinctUntilChanged()
+      .observeOn(AndroidSchedulers.mainThread())
+      .subscribe { widths ->
+        val wrapperWidth = widths.first
+        val coreWidth = widths.second
+        Log.d(TAG, "wrapperWidth: $wrapperWidth, coreWidth: $coreWidth")
+        recenter(coreWidth, wrapperWidth)
+      }
+  }
+
+  fun detach() {
+    wrapper.removeOnLayoutChangeListener(emitNewWrapperWidth)
+    buttonHolder.removeOnLayoutChangeListener(emitNewCoreWidth)
+    listener?.dispose()
+    listener = null
+  }
 
-  @Synchronized
-  fun recenter(buttonHolder: View, wrapper: View) {
-    buttonHolder.measure(View.MeasureSpec.UNSPECIFIED, View.MeasureSpec.UNSPECIFIED)
-    buttonHolder.layout(0, 0, buttonHolder.measuredWidth, buttonHolder.measuredHeight)
-    val buttonHolderCoreWidth = buttonHolder.run { width - (paddingLeft + paddingRight) }
-    val extraSpace = wrapper.width - buttonHolderCoreWidth
+  fun recenter(buttonHolderCoreWidth: Int, wrapperWidth: Int) {
+    val extraSpace = wrapperWidth - buttonHolderCoreWidth
     val horizontalPadding = if (extraSpace >= 0)
       (extraSpace / 2f).toInt()
     else

app/src/main/java/org/thoughtcrime/securesms/conversation/AttachmentKeyboardButtonList.kt

@@ -28,29 +28,26 @@ class AttachmentKeyboardButtonList @JvmOverloads constructor(
 
   private val inflater = LayoutInflater.from(context)
   private val inner: LinearLayout
-  private val recenterOnWidthChange: OnLayoutChangeListener
+
+  private val recenterHelper: AttachmentButtonCenterHelper
   var onButtonClicked: Consumer<AttachmentKeyboardButton> = Consumer { _ -> }
 
   private var currentButtons: List<AttachmentKeyboardButton> = listOf()
 
   init {
     inflate(context, R.layout.attachment_keyboard_button_list, this)
     inner = findViewById(R.id.attachment_keyboard_button_list_inner_linearlayout)
-    recenterOnWidthChange = OnLayoutChangeListener { _, left, _, right, _, oldLeft, _, oldRight, _ ->
-      if (oldRight - oldLeft == right - left)
-        return@OnLayoutChangeListener
-      AttachmentButtonCenterHelper.recenter(inner, this)
-    }
+    recenterHelper = AttachmentButtonCenterHelper(inner, this)
   }
 
   override fun onAttachedToWindow() {
     super.onAttachedToWindow()
-    addOnLayoutChangeListener(recenterOnWidthChange)
+    recenterHelper.attach()
   }
 
   override fun onDetachedFromWindow() {
     super.onDetachedFromWindow()
-    removeOnLayoutChangeListener(recenterOnWidthChange)
+    recenterHelper.detach()
   }
 
   fun setButtons(newButtons: List<AttachmentKeyboardButton>) {
@@ -60,7 +57,6 @@ class AttachmentKeyboardButtonList @JvmOverloads constructor(
     currentButtons = newButtons
     inner.removeAllViews()
     newButtons.forEach { inner += inflateButton(it) }
-    inner.post { AttachmentButtonCenterHelper.recenter(inner, this) }
   }
 
   private fun inflateButton(button: AttachmentKeyboardButton): ButtonStripItemView {