diff --git a/adapter/src/main/kotlin/io/goooler/demoapp/adapter/rv/core/BaseRvAdapter.kt b/adapter/src/main/kotlin/io/goooler/demoapp/adapter/rv/core/BaseRvAdapter.kt
index d83b9d2e8..bc7b38559 100644
--- a/adapter/src/main/kotlin/io/goooler/demoapp/adapter/rv/core/BaseRvAdapter.kt
+++ b/adapter/src/main/kotlin/io/goooler/demoapp/adapter/rv/core/BaseRvAdapter.kt
@@ -13,13 +13,12 @@ import kotlinx.collections.immutable.toImmutableList
  * @since 1.0.0
  */
 abstract class BaseRvAdapter<M : IVhModelType> private constructor(
-  private val delegate: IRvAdapterDelegate.Impl<M, BaseRvAdapter<M>>,
+  private val delegate: IMutableRvAdapter.Impl<M, BaseRvAdapter<M>>,
 ) : RecyclerView.Adapter<BindingViewHolder>(),
   IRvBinding<M>,
-  IMutableRvAdapter<M>,
-  IRvAdapterDelegate<M, BindingViewHolder> by delegate {
+  IMutableRvAdapter<M, BindingViewHolder> by delegate {
 
-  constructor() : this(IRvAdapterDelegate.Impl()) {
+  constructor() : this(IMutableRvAdapter.Impl()) {
     @Suppress("LeakingThis")
     delegate.adapter = this
   }
diff --git a/adapter/src/main/kotlin/io/goooler/demoapp/adapter/rv/core/IRvAdapter.kt b/adapter/src/main/kotlin/io/goooler/demoapp/adapter/rv/core/IRvAdapter.kt
index 3eba3cd5a..49eaf1a80 100644
--- a/adapter/src/main/kotlin/io/goooler/demoapp/adapter/rv/core/IRvAdapter.kt
+++ b/adapter/src/main/kotlin/io/goooler/demoapp/adapter/rv/core/IRvAdapter.kt
@@ -1,8 +1,27 @@
 package io.goooler.demoapp.adapter.rv.core
 
+import android.view.ViewGroup
+import androidx.annotation.LayoutRes
 import androidx.databinding.BindingAdapter
 import androidx.databinding.ViewDataBinding
+import androidx.recyclerview.widget.GridLayoutManager
 import androidx.recyclerview.widget.RecyclerView
+import androidx.recyclerview.widget.StaggeredGridLayoutManager
+import io.goooler.demoapp.adapter.rv.core.ISpanSize.Companion.SPAN_SIZE_FULL
+
+/**
+ * Keep the same signature as [RecyclerView.Adapter].
+ *
+ * Workaround for [KT-21955](https://youtrack.jetbrains.com/issue/KT-21955).
+ */
+internal interface RecyclerViewAdapter<VH : RecyclerView.ViewHolder> {
+  fun onAttachedToRecyclerView(recyclerView: RecyclerView)
+  fun onDetachedFromRecyclerView(recyclerView: RecyclerView)
+  fun onCreateViewHolder(parent: ViewGroup, viewType: Int): VH
+  fun onBindViewHolder(holder: BindingViewHolder, position: Int)
+  fun onBindViewHolder(holder: BindingViewHolder, position: Int, payloads: List<Any>)
+  fun getItemViewType(position: Int): Int
+}
 
 /**
  * Created on 2020/10/21.
@@ -13,7 +32,7 @@ import androidx.recyclerview.widget.RecyclerView
  * @version 1.0.0
  * @since 1.0.0
  */
-internal interface IRvAdapter<M : IVhModelType> {
+internal interface IRvAdapter<M : IVhModelType, VH : RecyclerView.ViewHolder> : RecyclerViewAdapter<VH> {
 
   /**
    * Get data list.
@@ -39,9 +58,119 @@ internal interface IRvAdapter<M : IVhModelType> {
    * Get item by position.
    */
   operator fun get(position: Int): M?
+
+  @Suppress("TooManyFunctions")
+  open class Impl<M : IVhModelType, AP> : IRvAdapter<M, BindingViewHolder>
+    where AP : IRvAdapter<M, BindingViewHolder>,
+          AP : IRvBinding<M>,
+          AP : RecyclerView.Adapter<BindingViewHolder> {
+
+    private val ivdManager = ViewTypeDelegateManager<M>()
+
+    @Suppress("PropertyName", "ktlint:standard:backing-property-naming")
+    protected val _list = mutableListOf<M>()
+
+    lateinit var adapter: AP
+
+    override val list: List<M> get() = _list
+
+    override fun onAttachedToRecyclerView(recyclerView: RecyclerView) {
+      initManager(ivdManager)
+      fixSpanSize(recyclerView)
+    }
+
+    override fun onDetachedFromRecyclerView(recyclerView: RecyclerView) {
+      ivdManager.clear()
+      recyclerView.adapter = null
+    }
+
+    override operator fun get(position: Int): M = _list.getOrElse(position) {
+      // Override get in adapters as a fallback.
+      adapter[position] ?: error("No such a element in position $position in adapter $adapter.")
+    }
+
+    @LayoutRes
+    override fun getItemViewType(position: Int): Int = get(position).viewType
+
+    override fun onCreateViewHolder(
+      parent: ViewGroup,
+      @LayoutRes viewType: Int,
+    ): BindingViewHolder = BindingViewHolder.create(parent, viewType).also {
+      adapter.onCreateVHForAll(it.binding)
+      ivdManager.onCreateVH(it.binding, viewType)
+    }
+
+    override fun onBindViewHolder(holder: BindingViewHolder, position: Int) {
+      onBindViewHolder(holder, position, emptyList())
+    }
+
+    override fun onBindViewHolder(holder: BindingViewHolder, position: Int, payloads: List<Any>) {
+      get(position).let {
+        setFullSpan(holder, it)
+        adapter.onBindVHForAll(holder.binding, it, payloads)
+        ivdManager.onBindVH(holder.binding, it, payloads)
+        holder.binding.executePendingBindings()
+      }
+    }
+
+    override fun onCreateVHForAll(binding: ViewDataBinding) {
+      adapter.onCreateVH(binding)
+    }
+
+    override fun onBindVHForAll(binding: ViewDataBinding, model: M, payloads: List<Any>) {
+      adapter.onBindVH(binding, model, payloads)
+    }
+
+    /**
+     * Transform data list. Always return a new list.
+     */
+    fun transform(original: List<M>): List<M> {
+      val result = mutableListOf<M>()
+      original.forEach { findLeaf(it, result) }
+      return result
+    }
+
+    /**
+     * Recursively traversing all leaf nodes.
+     */
+    @Suppress("UNCHECKED_CAST")
+    private fun findLeaf(model: M, list: MutableList<M>) {
+      if (model is IVhModelWrapper<*>) {
+        if (model.viewType != -1) list += model
+        model.subList.forEach { findLeaf(it as M, list) }
+      } else {
+        list += model
+      }
+    }
+
+    /**
+     * Fix span size when recyclerView's layoutManager is [GridLayoutManager].
+     */
+    private fun fixSpanSize(recyclerView: RecyclerView) {
+      (recyclerView.layoutManager as? GridLayoutManager)?.let {
+        it.spanSizeLookup = object : GridLayoutManager.SpanSizeLookup() {
+          override fun getSpanSize(position: Int): Int {
+            (get(position) as? ISpanSize)?.spanSize?.let { size ->
+              return if (size == SPAN_SIZE_FULL) it.spanCount else size
+            }
+            return it.spanCount
+          }
+        }
+      }
+    }
+
+    /**
+     * Set full span when recyclerView's layoutManager is [StaggeredGridLayoutManager].
+     */
+    private fun setFullSpan(holder: RecyclerView.ViewHolder, item: M) {
+      (holder.itemView.layoutParams as? StaggeredGridLayoutManager.LayoutParams)?.let {
+        it.isFullSpan = (item as? ISpanSize)?.spanSize == SPAN_SIZE_FULL
+      }
+    }
+  }
 }
 
-internal interface IMutableRvAdapter<M : IVhModelType> : IRvAdapter<M> {
+internal interface IMutableRvAdapter<M : IVhModelType, VH : BindingViewHolder> : IRvAdapter<M, VH> {
 
   /**
    * Set or Get data list.
@@ -56,16 +185,65 @@ internal interface IMutableRvAdapter<M : IVhModelType> : IRvAdapter<M> {
   fun removeItem(index: Int)
 
   fun removeItem(item: M)
+
+  class Impl<M : IVhModelType, AP> :
+    IRvAdapter.Impl<M, AP>(),
+    IMutableRvAdapter<M, BindingViewHolder>
+    where AP : IRvAdapter<M, BindingViewHolder>,
+          AP : IRvBinding<M>,
+          AP : RecyclerView.Adapter<BindingViewHolder> {
+
+    override var list: List<M>
+      get() = _list
+      set(value) {
+        _list.clear()
+        _list.addAll(transform(value))
+      }
+
+    override fun refreshItems(items: List<M>) {
+      refreshItems(items, adapter::notifyItemChanged)
+    }
+
+    override fun removeItem(index: Int) {
+      removeItem(index = index, adapter::notifyItemRemoved)
+    }
+
+    override fun removeItem(item: M) {
+      removeItem(item = item, adapter::notifyItemRemoved)
+    }
+
+    /**
+     * Compare the list to find the same items and refresh them.
+     */
+    private inline fun refreshItems(items: List<M>, notify: (Int) -> Unit) {
+      transform(items).forEach {
+        if (it in _list) {
+          notify(_list.indexOf(it))
+        }
+      }
+    }
+
+    private inline fun removeItem(index: Int, notify: (Int) -> Unit) {
+      _list.removeAt(index)
+      notify(index)
+    }
+
+    private inline fun removeItem(item: M, notify: (Int) -> Unit) {
+      _list.indexOf(item).takeIf { it != -1 }?.let {
+        removeItem(it, notify)
+      }
+    }
+  }
 }
 
 @BindingAdapter("binding_rv_dataList")
 internal fun <M : IVhModelType> RecyclerView.bindingSetList(list: List<M>?) {
   @Suppress("UNCHECKED_CAST")
-  (adapter as? IMutableRvAdapter<M>)?.list = list.orEmpty()
+  (adapter as? IMutableRvAdapter<M, *>)?.list = list.orEmpty()
 }
 
 @BindingAdapter("binding_rv_refreshItems")
 internal fun <M : IVhModelType> RecyclerView.bindingRefreshItems(items: List<M>?) {
   @Suppress("UNCHECKED_CAST")
-  (adapter as? IMutableRvAdapter<M>)?.refreshItems(items.orEmpty())
+  (adapter as? IMutableRvAdapter<M, *>)?.refreshItems(items.orEmpty())
 }
diff --git a/adapter/src/main/kotlin/io/goooler/demoapp/adapter/rv/core/IRvAdapterDelegate.kt b/adapter/src/main/kotlin/io/goooler/demoapp/adapter/rv/core/IRvAdapterDelegate.kt
deleted file mode 100644
index 7e4e7c8f3..000000000
--- a/adapter/src/main/kotlin/io/goooler/demoapp/adapter/rv/core/IRvAdapterDelegate.kt
+++ /dev/null
@@ -1,175 +0,0 @@
-package io.goooler.demoapp.adapter.rv.core
-
-import android.view.ViewGroup
-import androidx.annotation.LayoutRes
-import androidx.databinding.ViewDataBinding
-import androidx.recyclerview.widget.GridLayoutManager
-import androidx.recyclerview.widget.RecyclerView
-import androidx.recyclerview.widget.StaggeredGridLayoutManager
-import io.goooler.demoapp.adapter.rv.core.ISpanSize.Companion.SPAN_SIZE_FULL
-
-/**
- * Keep the same signature as [RecyclerView.Adapter].
- *
- * Workaround for [KT-21955](https://youtrack.jetbrains.com/issue/KT-21955).
- */
-internal interface RecyclerViewAdapter<VH : RecyclerView.ViewHolder> {
-  fun onAttachedToRecyclerView(recyclerView: RecyclerView)
-  fun onDetachedFromRecyclerView(recyclerView: RecyclerView)
-  fun onCreateViewHolder(parent: ViewGroup, viewType: Int): VH
-  fun onBindViewHolder(holder: BindingViewHolder, position: Int)
-  fun onBindViewHolder(holder: BindingViewHolder, position: Int, payloads: List<Any>)
-  fun getItemViewType(position: Int): Int
-}
-
-internal interface IRvAdapterDelegate<M : IVhModelType, VH : BindingViewHolder> :
-  IMutableRvAdapter<M>,
-  RecyclerViewAdapter<VH> {
-
-  @Suppress("TooManyFunctions")
-  class Impl<M : IVhModelType, AP> : IRvAdapterDelegate<M, BindingViewHolder>
-    where AP : IRvAdapter<M>,
-          AP : IRvBinding<M>,
-          AP : RecyclerView.Adapter<BindingViewHolder> {
-
-    private val ivdManager = ViewTypeDelegateManager<M>()
-    private val _list = mutableListOf<M>()
-
-    lateinit var adapter: AP
-
-    override var list: List<M>
-      get() = _list
-      set(value) {
-        _list.clear()
-        _list.addAll(transform(value))
-      }
-
-    override fun onAttachedToRecyclerView(recyclerView: RecyclerView) {
-      initManager(ivdManager)
-      fixSpanSize(recyclerView)
-    }
-
-    override fun onDetachedFromRecyclerView(recyclerView: RecyclerView) {
-      ivdManager.clear()
-      recyclerView.adapter = null
-    }
-
-    override operator fun get(position: Int): M = _list.getOrElse(position) {
-      // Override get in adapters as a fallback.
-      adapter[position] ?: error("No such a element in position $position in adapter $adapter.")
-    }
-
-    @LayoutRes
-    override fun getItemViewType(position: Int): Int = get(position).viewType
-
-    override fun onCreateViewHolder(
-      parent: ViewGroup,
-      @LayoutRes viewType: Int,
-    ): BindingViewHolder = BindingViewHolder.create(parent, viewType).also {
-      adapter.onCreateVHForAll(it.binding)
-      ivdManager.onCreateVH(it.binding, viewType)
-    }
-
-    override fun onBindViewHolder(holder: BindingViewHolder, position: Int) {
-      onBindViewHolder(holder, position, emptyList())
-    }
-
-    override fun onBindViewHolder(holder: BindingViewHolder, position: Int, payloads: List<Any>) {
-      get(position).let {
-        setFullSpan(holder, it)
-        adapter.onBindVHForAll(holder.binding, it, payloads)
-        ivdManager.onBindVH(holder.binding, it, payloads)
-        holder.binding.executePendingBindings()
-      }
-    }
-
-    override fun onCreateVHForAll(binding: ViewDataBinding) {
-      adapter.onCreateVH(binding)
-    }
-
-    override fun onBindVHForAll(binding: ViewDataBinding, model: M, payloads: List<Any>) {
-      adapter.onBindVH(binding, model, payloads)
-    }
-
-    override fun refreshItems(items: List<M>) {
-      refreshItems(items, adapter::notifyItemChanged)
-    }
-
-    override fun removeItem(index: Int) {
-      removeItem(index = index, adapter::notifyItemRemoved)
-    }
-
-    override fun removeItem(item: M) {
-      removeItem(item = item, adapter::notifyItemRemoved)
-    }
-
-    /**
-     * Transform data list. Always return a new list.
-     */
-    fun transform(original: List<M>): List<M> {
-      val result = mutableListOf<M>()
-      original.forEach { findLeaf(it, result) }
-      return result
-    }
-
-    /**
-     * Compare the list to find the same items and refresh them.
-     */
-    private inline fun refreshItems(items: List<M>, notify: (Int) -> Unit) {
-      transform(items).forEach {
-        if (it in _list) {
-          notify(_list.indexOf(it))
-        }
-      }
-    }
-
-    private inline fun removeItem(index: Int, notify: (Int) -> Unit) {
-      _list.removeAt(index)
-      notify(index)
-    }
-
-    private inline fun removeItem(item: M, notify: (Int) -> Unit) {
-      _list.indexOf(item).takeIf { it != -1 }?.let {
-        removeItem(it, notify)
-      }
-    }
-
-    /**
-     * Recursively traversing all leaf nodes.
-     */
-    @Suppress("UNCHECKED_CAST")
-    private fun findLeaf(model: M, list: MutableList<M>) {
-      if (model is IVhModelWrapper<*>) {
-        if (model.viewType != -1) list += model
-        model.subList.forEach { findLeaf(it as M, list) }
-      } else {
-        list += model
-      }
-    }
-
-    /**
-     * Fix span size when recyclerView's layoutManager is [GridLayoutManager].
-     */
-    private fun fixSpanSize(recyclerView: RecyclerView) {
-      (recyclerView.layoutManager as? GridLayoutManager)?.let {
-        it.spanSizeLookup = object : GridLayoutManager.SpanSizeLookup() {
-          override fun getSpanSize(position: Int): Int {
-            (get(position) as? ISpanSize)?.spanSize?.let { size ->
-              return if (size == SPAN_SIZE_FULL) it.spanCount else size
-            }
-            return it.spanCount
-          }
-        }
-      }
-    }
-
-    /**
-     * Set full span when recyclerView's layoutManager is [StaggeredGridLayoutManager].
-     */
-    private fun setFullSpan(holder: RecyclerView.ViewHolder, item: M) {
-      (holder.itemView.layoutParams as? StaggeredGridLayoutManager.LayoutParams)?.let {
-        it.isFullSpan = (item as? ISpanSize)?.spanSize == SPAN_SIZE_FULL
-      }
-    }
-  }
-}
diff --git a/adapter/src/main/kotlin/io/goooler/demoapp/adapter/rv/diff/BaseRvDiffAdapter.kt b/adapter/src/main/kotlin/io/goooler/demoapp/adapter/rv/diff/BaseRvDiffAdapter.kt
index 631ed3293..faafb4ba5 100644
--- a/adapter/src/main/kotlin/io/goooler/demoapp/adapter/rv/diff/BaseRvDiffAdapter.kt
+++ b/adapter/src/main/kotlin/io/goooler/demoapp/adapter/rv/diff/BaseRvDiffAdapter.kt
@@ -5,7 +5,6 @@ import androidx.recyclerview.widget.DiffUtil
 import androidx.recyclerview.widget.ListAdapter
 import io.goooler.demoapp.adapter.rv.core.BindingViewHolder
 import io.goooler.demoapp.adapter.rv.core.IMutableRvAdapter
-import io.goooler.demoapp.adapter.rv.core.IRvAdapterDelegate
 import io.goooler.demoapp.adapter.rv.core.IRvBinding
 import kotlinx.collections.immutable.toImmutableList
 
@@ -20,21 +19,20 @@ import kotlinx.collections.immutable.toImmutableList
  */
 abstract class BaseRvDiffAdapter<M : IDiffVhModelType> private constructor(
   asyncDifferConfig: AsyncDifferConfig<M>,
-  private val delegate: IRvAdapterDelegate.Impl<M, BaseRvDiffAdapter<M>>,
+  private val delegate: IMutableRvAdapter.Impl<M, BaseRvDiffAdapter<M>>,
 ) : ListAdapter<M, BindingViewHolder>(asyncDifferConfig),
   IRvBinding<M>,
-  IMutableRvAdapter<M>,
-  IRvAdapterDelegate<M, BindingViewHolder> by delegate {
+  IMutableRvAdapter<M, BindingViewHolder> by delegate {
 
   constructor(callback: DiffCallback<M> = DiffCallback()) : this(
     AsyncDifferConfig.Builder(callback).build(),
-    IRvAdapterDelegate.Impl(),
+    IMutableRvAdapter.Impl(),
   ) {
     @Suppress("LeakingThis")
     delegate.adapter = this
   }
 
-  constructor(config: AsyncDifferConfig<M>) : this(config, IRvAdapterDelegate.Impl()) {
+  constructor(config: AsyncDifferConfig<M>) : this(config, IMutableRvAdapter.Impl()) {
     @Suppress("LeakingThis")
     delegate.adapter = this
   }
diff --git a/adapter/src/main/kotlin/io/goooler/demoapp/adapter/rv/paging/BaseRvPagingAdapter.kt b/adapter/src/main/kotlin/io/goooler/demoapp/adapter/rv/paging/BaseRvPagingAdapter.kt
index 2635cf6d4..8245e9c31 100644
--- a/adapter/src/main/kotlin/io/goooler/demoapp/adapter/rv/paging/BaseRvPagingAdapter.kt
+++ b/adapter/src/main/kotlin/io/goooler/demoapp/adapter/rv/paging/BaseRvPagingAdapter.kt
@@ -7,7 +7,6 @@ import androidx.paging.PagingDataAdapter
 import androidx.recyclerview.widget.RecyclerView
 import io.goooler.demoapp.adapter.rv.core.BindingViewHolder
 import io.goooler.demoapp.adapter.rv.core.IRvAdapter
-import io.goooler.demoapp.adapter.rv.core.IRvAdapterDelegate
 import io.goooler.demoapp.adapter.rv.core.IRvBinding
 import io.goooler.demoapp.adapter.rv.diff.DiffCallback
 import io.goooler.demoapp.adapter.rv.diff.IDiffVhModelType
@@ -21,11 +20,10 @@ import io.goooler.demoapp.adapter.rv.diff.IDiffVhModelType
  */
 abstract class BaseRvPagingAdapter<M : IDiffVhModelType> private constructor(
   callback: DiffCallback<M>,
-  private val delegate: IRvAdapterDelegate.Impl<M, BaseRvPagingAdapter<M>>,
+  private val delegate: IRvAdapter.Impl<M, BaseRvPagingAdapter<M>>,
 ) : PagingDataAdapter<M, BindingViewHolder>(callback),
   IRvBinding<M>,
-  IRvAdapter<M>,
-  IRvAdapterDelegate<M, BindingViewHolder> by delegate {
+  IRvAdapter<M, BindingViewHolder> by delegate {
 
   var onLoadStatusListener: OnLoadStatusListener? = null
 
@@ -33,7 +31,7 @@ abstract class BaseRvPagingAdapter<M : IDiffVhModelType> private constructor(
     get() = snapshot().items
     set(_) = error("You shouldn't call this setter. Use submitData() instead.")
 
-  constructor(callback: DiffCallback<M> = DiffCallback()) : this(callback, IRvAdapterDelegate.Impl()) {
+  constructor(callback: DiffCallback<M> = DiffCallback()) : this(callback, IRvAdapter.Impl()) {
     @Suppress("LeakingThis")
     delegate.adapter = this
   }