Enable recycling of views within groups (#657)

* Enable recycling of views within groups

* cleanup

* revert to kotlin 1.2.71

* fix test

build.gradle

@@ -9,7 +9,7 @@ buildscript {
     jcenter()
   }
   dependencies {
-    classpath "com.android.tools.build:gradle:3.2.1"
+    classpath "com.android.tools.build:gradle:$ANDROID_PLUGIN_VERSION"
     classpath "org.jetbrains.kotlin:kotlin-gradle-plugin:$KOTLIN_VERSION"
     classpath 'com.bmuschko:gradle-nexus-plugin:2.3.1'
   }
@@ -83,6 +83,6 @@ def getRepositoryPassword() {
 }
 
 task wrapper(type: Wrapper) {
-  gradleVersion = '4.9'
+  gradleVersion = '4.10.2'
   distributionUrl = "https://services.gradle.org/distributions/gradle-$gradleVersion-all.zip"
 }

epoxy-adapter/src/main/java/com/airbnb/epoxy/ActivityRecyclerPool.kt

@@ -0,0 +1,106 @@
+package com.airbnb.epoxy
+
+import android.app.Activity
+import android.content.Context
+import android.os.Build
+import androidx.core.view.ViewCompat
+import androidx.lifecycle.Lifecycle
+import androidx.lifecycle.LifecycleObserver
+import androidx.lifecycle.LifecycleOwner
+import androidx.lifecycle.OnLifecycleEvent
+import androidx.recyclerview.widget.RecyclerView
+import java.lang.ref.WeakReference
+import java.util.ArrayList
+
+internal class ActivityRecyclerPool {
+
+    /**
+     * Store one unique pool per activity. They are cleared out when activities are destroyed, so this
+     * only needs to hold pools for active activities.
+     */
+    private val pools = ArrayList<PoolReference>(5)
+
+    @JvmOverloads
+    fun getPool(
+        context: Context,
+        poolFactory: () -> RecyclerView.RecycledViewPool = { UnboundedViewPool() }
+    ): PoolReference {
+
+        val iterator = pools.iterator()
+        var poolToUse: PoolReference? = null
+
+        while (iterator.hasNext()) {
+            val poolReference = iterator.next()
+            when {
+                poolReference.context === context -> {
+                    if (poolToUse != null) {
+                        throw IllegalStateException("A pool was already found")
+                    }
+                    poolToUse = poolReference
+                    // finish iterating to remove any old contexts
+                }
+                poolReference.context.isActivityDestroyed() -> {
+                    // A pool from a different activity that was destroyed.
+                    // Clear the pool references to allow the activity to be GC'd
+                    poolReference.viewPool.clear()
+                    iterator.remove()
+                }
+            }
+        }
+
+        if (poolToUse == null) {
+            poolToUse = PoolReference(context, poolFactory(), this)
+            (context as? LifecycleOwner)?.lifecycle?.addObserver(poolToUse)
+            pools.add(poolToUse)
+        }
+
+        return poolToUse
+    }
+
+    fun clearIfDestroyed(pool: PoolReference) {
+        if (pool.context.isActivityDestroyed()) {
+            pool.viewPool.clear()
+            pools.remove(pool)
+        }
+    }
+}
+
+internal class PoolReference(
+    context: Context,
+    val viewPool: RecyclerView.RecycledViewPool,
+    private val parent: ActivityRecyclerPool
+) : LifecycleObserver {
+    private val contextReference: WeakReference<Context> = WeakReference(context)
+
+    val context: Context? get() = contextReference.get()
+
+    fun clearIfDestroyed() {
+        parent.clearIfDestroyed(this)
+    }
+
+    @OnLifecycleEvent(Lifecycle.Event.ON_DESTROY)
+    fun onContextDestroyed() {
+        clearIfDestroyed()
+    }
+}
+
+internal fun Context?.isActivityDestroyed(): Boolean {
+    if (this == null) {
+        return true
+    }
+
+    if (this !is Activity) {
+        return false
+    }
+
+    if (isFinishing) {
+        return true
+    }
+
+    return if (Build.VERSION.SDK_INT >= 17) {
+        isDestroyed
+    } else {
+        // Use this as a proxy for being destroyed on older devices
+        !ViewCompat.isAttachedToWindow(window.decorView)
+    }
+}

epoxy-adapter/src/main/java/com/airbnb/epoxy/BaseEpoxyAdapter.java

@@ -149,7 +149,7 @@ protected BoundViewHolders getBoundViewHolders() {
 
   @Override
   public int getItemViewType(int position) {
-    return viewTypeManager.getViewType(getModelForPosition(position));
+    return viewTypeManager.getViewTypeAndRememberModel(getModelForPosition(position));
   }
 
   @Override