Implement animated color lerp for material toolbars.

app/src/main/java/org/thoughtcrime/securesms/util/Material3OnScrollHelper.kt

@@ -1,10 +1,12 @@
 package org.thoughtcrime.securesms.util
 
+import android.animation.ValueAnimator
 import android.app.Activity
-import android.os.Build
 import android.view.View
+import androidx.annotation.ColorInt
 import androidx.core.content.ContextCompat
 import androidx.recyclerview.widget.RecyclerView
+import com.google.android.material.animation.ArgbEvaluatorCompat
 import org.thoughtcrime.securesms.R
 import org.thoughtcrime.securesms.util.views.Stub
 
@@ -13,20 +15,36 @@ import org.thoughtcrime.securesms.util.views.Stub
  * This can be used to appropriately tint toolbar backgrounds. Also can emit the state change
  * for other purposes.
  */
-class Material3OnScrollHelper(
+open class Material3OnScrollHelper(
+  private val activity: Activity,
   private val views: List<View>,
-  private val viewStubs: List<Stub<out View>> = emptyList(),
-  private val onActiveStateChanged: (Boolean) -> Unit
-) : RecyclerView.OnScrollListener() {
+  private val viewStubs: List<Stub<out View>> = emptyList()
+) {
 
-  constructor(activity: Activity, views: List<View>, viewStubs: List<Stub<out View>>) : this(views, viewStubs, { updateStatusBarColor(activity, it) })
+  open val activeColorRes: Int = R.color.signal_colorSurface2
+  open val inactiveColorRes: Int = R.color.signal_colorBackground
 
-  constructor(activity: Activity, view: View) : this(listOf(view), emptyList(), { updateStatusBarColor(activity, it) })
+  constructor(activity: Activity, view: View) : this(activity, listOf(view), emptyList())
 
+  private var animator: ValueAnimator? = null
   private var active: Boolean? = null
+  private val scrollListener = OnScrollListener()
 
-  override fun onScrolled(recyclerView: RecyclerView, dx: Int, dy: Int) {
-    updateActiveState(recyclerView.canScrollVertically(-1))
+  fun attach(recyclerView: RecyclerView) {
+    recyclerView.addOnScrollListener(scrollListener)
+    scrollListener.onScrolled(recyclerView, 0, 0)
+  }
+
+  /**
+   * Cancels any currently running scroll animation and sets the color immediately.
+   */
+  fun setColorImmediate() {
+    if (active == null) {
+      return
+    }
+
+    animator?.cancel()
+    setColor(ContextCompat.getColor(activity, if (active == true) activeColorRes else inactiveColorRes))
   }
 
   private fun updateActiveState(isActive: Boolean) {
@@ -34,23 +52,41 @@ class Material3OnScrollHelper(
       return
     }
 
+    val hadActiveState = active != null
     active = isActive
 
     views.forEach { it.isActivated = isActive }
     viewStubs.filter { it.resolved() }.forEach { it.get().isActivated = isActive }
 
-    onActiveStateChanged(isActive)
-  }
+    if (animator?.isRunning == true) {
+      animator?.reverse()
+    } else {
+      val startColor = ContextCompat.getColor(activity, if (isActive) inactiveColorRes else activeColorRes)
+      val endColor = ContextCompat.getColor(activity, if (isActive) activeColorRes else inactiveColorRes)
 
-  companion object {
-    fun updateStatusBarColor(activity: Activity, isActive: Boolean) {
-      if (Build.VERSION.SDK_INT > 21) {
-        if (isActive) {
-          WindowUtil.setStatusBarColor(activity.window, ContextCompat.getColor(activity, R.color.signal_colorSurface2))
-        } else {
-          WindowUtil.setStatusBarColor(activity.window, ContextCompat.getColor(activity, R.color.signal_colorBackground))
+      if (hadActiveState) {
+        animator = ValueAnimator.ofObject(ArgbEvaluatorCompat(), startColor, endColor).apply {
+          duration = 200
+          addUpdateListener { animator ->
+            setColor(animator.animatedValue as Int)
+          }
+          start()
         }
+      } else {
+        setColorImmediate()
       }
     }
   }
+
+  private fun setColor(@ColorInt color: Int) {
+    WindowUtil.setStatusBarColor(activity.window, color)
+    views.forEach { it.setBackgroundColor(color) }
+    viewStubs.filter { it.resolved() }.forEach { it.get().setBackgroundColor(color) }
+  }
+
+  private inner class OnScrollListener : RecyclerView.OnScrollListener() {
+    override fun onScrolled(recyclerView: RecyclerView, dx: Int, dy: Int) {
+      updateActiveState(recyclerView.canScrollVertically(-1))
+    }
+  }
 }